JP3507827B2 - Multi-output switching power supply circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-output switching power supply circuit which performs constant voltage control using a mag amplifier.

[0002]

2. Description of the Related Art FIG. 8 shows a conventional circuit configuration using a mag-amplifier for constant voltage control of a multi-output switching power supply circuit.

On the primary side of the transformer 20 of this multi-output switching power supply circuit, a DC power supply unit 1, an input smoothing capacitor 2, a starting resistor 3, a PWM control circuit 4, detection resistors 5 and 6, a capacitor 7, Smoothing choke coil 8, rectifying diode 9, commutation diode 10, main switch (for example, N-channel MOS transistor, hereinafter,
11 called “NMOS”.

On the primary side of the transformer 20, a primary winding 21,
The auxiliary winding 22 is arranged, and on the secondary side, secondary windings 23a, 23b, 23c ... Are provided for each output section.

On the secondary side of the transformer 20, a mag amplifier 31, a rectifying diode 32, and a commutating diode 3 are provided.
3, smoothing choke coil 34, capacitor 35, dummy resistor 36, constant voltage control circuit 37, detection resistor 38, 3
An output section A including a transistor 9, a transistor 40, a resistor 41, and a diode 42, and output sections B, C ... Having the same configuration as the output section A are provided. Load R on each output
L is connected.

The operating principle of the mag amplifier shown in FIG. 6 will now be described with reference to FIGS. As shown in FIG. 9, the mag-amplifier 31 is in the ON state when the pulse current having the pulse width x μs (microsecond) is flowing. Here, even if the pulse current is repeatedly turned on / off, the magnetizing state of the mag-amplifier 31 is set to the point A corresponding to the maximum value of the pulse current and the current zero, that is, the magnetic field zero, as shown in FIG. It only makes a round trip to and from the corresponding point B, and the same mag amplifier 31 remains in the ON state.
However, while the pulse current is off, the mag amp 3
As a slight current (that is, a reset current) flows in the direction 1 opposite to the pulse current, the magnetized state of the mag amplifier 31 moves to point C, and the mag amplifier 31 is turned off. In this state, even if the voltage E is applied to the mag-amplifier 31 in the positive direction, the current does not flow immediately, and from the relationship of magnetic flux (φ) = voltage time product (T × E), ΔT = Δφ / E Only the rise time is delayed and the flow starts. Pulse width modulation is performed by controlling the rise time delay ΔT by the reset current. Here, if x = ΔT, no current flows. In this formula, x represents the pulse width as described above. That is, Δ of the mag amplifier 31
Adjusting the width of φ changes the pulse current from 0 to 10
Pulse modulation is performed in the range of 0%.

Next, the operation of the conventional multi-output switching power supply circuit shown in FIG. 8 will be described. In this multi-output switching power supply circuit, the DC power supply unit 1 generates and outputs the DC input voltage V1. This DC input voltage V1
Are smoothed by the input smoothing capacitor 2.

The PWM control circuit 4 generates a control signal V4 having a pulse width corresponding to a predetermined frequency and detection voltage. The detected voltage is a pulsating voltage generated by rectifying an AC voltage generated in the auxiliary winding 22 provided on the primary side of the transformer 20 by the rectifying diode 9, and the pulsating voltage is generated by the smoothing choke coil 8 and the smoothing capacitor. It is smoothed by 7 to generate a DC output voltage. This DC output voltage is divided by the resistors 5 and 6, and the change is detected by the PWM control circuit 4 to be generated. That is, since the AC voltage appearing in the secondary winding 23a is determined by the turn ratio of the primary winding 21 and the secondary winding 23a, the AC voltage appearing in the secondary winding 23a by the auxiliary winding 22 is The output voltage is kept constant by creating a proportional AC voltage and controlling the pulse width by the PWM control circuit 4 based on the change of this AC voltage. The DC input voltage V1 is ON / OFF controlled by the NMOS 11 based on the control signal V4, and an AC voltage V11 having a predetermined frequency and a pulse width corresponding to the detection voltage is generated.
The AC voltage V11 is transformed by the transformer 20, and the transformer 2
0 secondary side windings 23a, 23b, 23c ... AC voltage V23 according to the turns ratio of the primary winding and the secondary winding.
a, V23b, V23c ... Occur.

The AC voltage V23a is converted into an AC voltage V31 having a pulse width corresponding to the reset current by ON / OFF control based on the reset current of the mag amplifier 31. The AC voltage V31 is rectified by the rectifying diode 32 to generate the pulsating voltage V32. Ripple voltage V3
The magnetic energy of 2 is stored in the smoothing choke coil 34. This magnetic energy is generated by the rectifying diode 32.
Is turned off and the commutation side diode 33 is turned on, the voltage is supplied to the smoothing capacitor 35. The pulsating voltage V32 is smoothed by the smoothing capacitor 35, and a DC output voltage is generated by the smoothing capacitor 35. Then, the DC output voltage V is output from the output unit to the load RL.

The DC output voltage is stabilized by utilizing the hysteresis characteristic of the mag amplifier 31. That is, the fluctuations of the DC output voltage are detected by the resistors 38 and 39, and the constant voltage control circuit 37 resets the reset current I42 for the mag amplifier 31 necessary for stabilizing the DC output voltage.
Is adjusted, and the mag-amp 31 is turned off via the transistor 40, the resistor 41, and the diode 42 during the OFF period.
A reset current flows to the amplifier 31. Then, the rising of the mag amplifier 31 during the ON state is controlled, and the DC output voltage is stabilized.

Next, the circuit configuration of a second conventional example of a multi-output switching power supply circuit using a mag amplifier for constant voltage control will be described with reference to FIG.

This multi-output switching power supply circuit has a main output section A and a plurality of sub-output sections B, C, ... The output section having the maximum output and small load fluctuation is used as the main output section A. ing. Then, the duty ratio of the switching on the primary side is negatively feedback controlled based on the fluctuation of the output voltage of the main output section A. The output voltage of the sub-output unit other than the main output unit A is generated by controlling the AC voltage having the duty ratio determined based on the output voltage of the main output unit A by the mag amplifier.

The multi-output switching power supply circuit of the second conventional example shown in FIG. 11 has a DC power supply unit 51, an input smoothing capacitor 52, a starting resistor 53, a P resistor on the primary side of the transformer 60.
WM control circuit 54, capacitor 55, smoothing choke coil 56, rectifying diode 57, commutation diode 5
8 and an NMOS 59 are provided.

The transformer 60 has a primary winding 61 and an auxiliary winding 62 on the primary side, and a secondary winding 63, an auxiliary winding 62 on the secondary side.
64, 65 ...

The main output section A comprises a rectifying diode 71, a commutating diode 72, a smoothing choke coin 73, a smoothing capacitor 74, a dummy resistor 75, and a constant voltage control circuit 76. The load RL1 is connected to the main output unit A. The sub output section B includes a mag amplifier 79, a rectifying side diode 80, a commutation side diode 81, a smoothing choke coil 82, a smoothing capacitor 83, a constant voltage control circuit 84, resistors 85 and 86, a transistor 87, and a resistor 8.
8 and a diode 89. The load RL2 is connected to the sub output unit B. The sub output unit C is also the sub output unit B.
The configuration is similar to that of the above, and the load RL3 is connected.

The AC voltage generated in the secondary winding 63 of the transformer 60 is rectified by the rectifying diode 71, and the pulsating voltage V7
1 is generated. The pulsating voltage V71 has its magnetic energy stored in the smoothing choke coil 73. This electromagnetic energy is supplied to the smoothing capacitor 74 when the rectification side diode 71 is off and the commutation side diode 72 is on. The pulsating voltage V71 is smoothed by the smoothing capacitor 74, and the smoothing capacitor 7
At 4, a DC output voltage V1 is generated. DC output voltage V1
Is applied to the dummy resistor 75 and the load RL1. When the DC output voltage V1 changes, it is detected by the constant voltage control circuit 76 and the detection signal V76 is generated. Detection signal V76
Is supplied to the PWM control circuit 54, and the pulse width of the AC voltage V59 is negatively feedback controlled by the PWM control circuit 54.

Based on the duty ratio determined by the PWM control circuit 54, the secondary winding 64 of the transformer 60 has
An AC voltage V64 is generated according to the turn ratio between the primary winding 61 and the secondary winding 64. This AC voltage V64 is rectified by the diode 80 via the mag-amplifier 79 of the sub output section B, and the pulsating voltage V80 is generated. The pulsating voltage V80 is
The magnetic energy is stored in the smoothing choke coil 82. This magnetic energy is generated by the rectifying diode 80.
Is turned off and the commutation diode 81 is turned on, the voltage is supplied to the smoothing capacitor 83. The pulsating voltage V80 is smoothed by the smoothing capacitor 83, and the DC output voltage V2 is generated by the smoothing capacitor 83. Then, the DC output voltage is output from the sub output unit B to the load RL2. In addition, the DC output voltage V
2 is detected, the constant voltage control circuit 84 adjusts the reset current I89 for the mag amplifier 79 required for stabilizing the DC output voltage V2, and the transistor 87,
A reset current I89 to the mag amplifier 79 flows through the resistor 88 and the diode 89 during the off period of the NMOS 59, that is, during the off period of the rectifying diode 80. Then, the rising time of the on-state period of the mag amplifier 79 is controlled, and the DC output voltage V2 is stabilized. The sub-output unit C also performs the same operation as the sub-output unit B.

As a third conventional example having a technical field similar to that of the present invention, there is a low loss output circuit disclosed in Japanese Patent No. 2927734. In this conventional example, as shown in FIG.
Mag amplifier MA connected to the secondary winding N2 of a transformer that outputs a rectangular wave AC voltage, rectifying element Q1 using a MOS-FET, rectifying element Q2 on the flywheel side, and rectifying these A low-loss output circuit having a smoothing choke coil CH for obtaining a DC output voltage by smoothing the rectified output of the element, and a smoothing choke coil for supplying a drive signal of a rectifying element Q2 on the flywheel side. It is characterized by being configured as follows.

According to this structure, a drive signal is supplied from the smoothing choke coil CH for smoothing the rectified output of the rectifying element using the MOS-FET to the rectifying element Q2 on the flywheel side, and the MOS-on the flywheel side. The FET Q2 is turned on. Therefore, after the polarity of the secondary winding of the transformer is reversed, the mag-amplifier is supplied to the MOS-FET on the smoothing choke coil side until it becomes saturated after the controlled time, and this MOS-FET can be turned on. The power loss on the flywheel side is reduced, and the overall loss reduction effect can be demonstrated.

[0020]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In a multi-output switching power supply circuit that performs constant voltage control using an amplifier, a diode is generally applied to a rectifier circuit. When a diode is used in the rectifier circuit, power loss due to the voltage drop of the diode causes a decrease in conversion efficiency, which is a problem.

Further, as the power supply voltage of the LSI is lowered, the demand for outputs such as + 3.3V, + 2.5V, and + 1.8V is increasing, but the voltage drop due to the diode is almost constant (about 0. Therefore, as the output voltage becomes lower, the problem that the ratio of the power loss in the diode rectifier circuit to the loss inside the power source becomes higher. Therefore, the conversion efficiency is further reduced, which is an obstacle to lowering the output voltage.

The problem that occurs in the conventional multi-output switching power supply circuit will be described with reference to the configuration of the conventional example 2 shown in FIG. In the conventional multi-output switching power supply circuit, if the dummy resistor 75 is not provided, the load RL1 connected to the main output portion A becomes light, for example, in a no-load state, and the load current is smoothed by a choke coil. When the current falls below the critical current of 73, the energy stored in the smoothing choke coil 73 is stored in the smoothing capacitor 74, and the DC output voltage V1 rises. In order to suppress the rise of the DC output voltage V1, the main switch (NMOS) 59 is controlled so that the time width of the ON state is narrowed. In this case, the pulse width of the AC voltage generated in the secondary winding 63 becomes short, and the voltage-time product (VT product, V;
The voltage applied to both ends of the mag-amplifier 79, T; the time until the mag-amplifier 79 is saturated) may not be secured, and the DC output voltage V2 of the sub output unit B may become unstable. As a countermeasure against this, by providing a dummy resistor 75 in the main output section A so that the time width of the ON state of the main switch (NMOS) 59 is not narrowed, the voltage time product required for the mag amplifier 79 is secured. It has become so. Therefore, the dummy resistor 75 always consumes power,
There was a problem that the power supply efficiency was lowered. Further, the dummy resistor 75 and a radiator (not shown) for radiating heat from the dummy resistor 75, or an electronic dummy circuit is required, which causes a problem that the number of components increases.

The low-loss output circuit of the above-mentioned conventional example 3 has a constant voltage control by a mag amplifier and a MOS-FET.
In a low-loss output circuit having a synchronous rectifying element of the MOS-FETQ, a drive signal of the flywheel-side rectifying element is supplied by a smoothing choke coil.
The purpose is to prevent simultaneous turn-on of Q1 and Q2 and suppress the occurrence of short-circuit current, and is not an invention relating to output voltage control, which is the technical field of the present invention.

Further, no consideration has been given to the influence of the malfunction occurring on the primary side of the transformer on the secondary side. For example, in the circuit configuration shown in FIG. 13, the core of the transformer is reset by free resonance due to the inductance of the transformer and the capacitance between the drain and the source of the NMOS 91. Therefore, a flyback voltage as shown in FIG. 14 is applied to the gate electrode of the NMOS 93. This deteriorates the conduction state of the NMOS 93.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multi-output switching power supply circuit capable of improving power supply conversion efficiency and easily achieving multi-output.

It is another object of the present invention to provide a multi-output switching power supply circuit which can stably generate a DC output voltage of a sub output section without providing a dummy resistance or an electronic dummy resistance in the main output section.

[0027]

In order to achieve the above object, the present invention according to claim 1 provides a DC power source for generating a DC input voltage and a second auxiliary winding which forms a transformer.
Detection circuit for detecting the voltage value of the alternating current voltage and a control signal generated by detecting a change in the voltage value of the second alternating current voltage for controlling the on / off of the direct current input voltage to obtain a predetermined frequency and a second frequency. A switching circuit for generating a first AC voltage having a pulse width corresponding to the AC voltage, a control circuit for generating a control signal based on a change in the voltage value of the second AC voltage detected by the detection circuit, and a switching circuit. By passing an exciting current through the primary winding of the transformer during the off period of the circuit,
An active clamp circuit that resets the core of the transformer is provided on the primary side of the transformer, and a third AC voltage generated in the secondary winding due to the transformation of the first AC voltage by the transformer is based on the reset current. A mag-amp that controls ON / OFF to generate a fourth AC voltage having a pulse width corresponding to the reset current, a rectifier circuit that rectifies the fourth AC voltage to generate a pulsating voltage, and a pulsating voltage is smoothed. Circuit for generating a direct current output voltage and applying the direct current output voltage to a load, and voltage control for detecting a change in the direct current output voltage and generating a reset current for negatively feedback controlling the fourth alternating voltage And a plurality of output sections each including a circuit on the secondary side of the transformer, the rectifying circuit depending on a voltage value of a fifth AC voltage generated in a second auxiliary winding provided on the secondary side of the transformer. On / off controlled to generate pulsating voltage A smoothing circuit having a first NMOS transistor, the smoothing circuit smoothes the pulsating voltage to generate a DC output voltage, applies the DC output voltage to a load, and a choke coil that stores magnetic energy due to the pulsating voltage. , The first NM according to the voltage value of the sixth AC voltage generated in the third auxiliary winding provided on the secondary side of the transformer.
A second NMOS transistor which is turned on when the OS is turned off and supplies electromagnetic energy stored in the choke coil to the smoothing capacitor;
The amplifier is inserted between the secondary winding and the first NMOS transistor.

According to a second aspect of the present invention, a DC power source for generating a DC input voltage, and a detection circuit for detecting the voltage value of the second AC voltage generated in the first auxiliary winding constituting the transformer,
The DC input voltage is ON / OFF controlled by the control signal generated by detecting the change in the voltage value of the second AC voltage,
A switching circuit that generates a first AC voltage having a predetermined frequency and a pulse width corresponding to the second AC voltage; and a change in the voltage value of the second AC voltage detected by the detection circuit,
And reset the core of the transformer by sending an exciting current to the primary winding of the transformer during the off period of the control circuit and the switching circuit that generates the control signal based on the level of the detection signal detected by the voltage change detection circuit. And a first pulsating voltage by rectifying the seventh AC voltage generated in the first secondary winding by the transformation of the first AC voltage by the transformer. First to generate
Of the rectifying circuit, a first smoothing circuit for smoothing the first pulsating voltage to generate a first DC output voltage, and applying the first DC output voltage to the load; A main output section having a voltage change detection circuit for detecting a change to generate a detection signal and supplying the detection signal to the control circuit; and a first output generated in the second secondary winding by the transformer transforming the first AC voltage. ON / OFF control of the AC voltage of 8 on the basis of the reset current to generate a ninth AC voltage having a pulse width corresponding to the reset current; and a mag-amp that rectifies the ninth AC voltage to generate a second AC voltage. A second rectifying circuit for generating a pulsating voltage and a second rectifying voltage for smoothing the second pulsating voltage to generate a second DC output voltage,
A second smoothing circuit for applying the DC output voltage of No. 2 to a load, a voltage control circuit for detecting a change in the second DC output voltage, and generating a reset current for performing negative feedback control of the ninth AC voltage, And a plurality of sub-output units each having a secondary output side of the transformer, and the first rectifier circuit performs on / off control by synchronizing the seventh AC voltage with the timing of switching in the switching circuit. , A first NMOS transistor for generating a first pulsating voltage, the first smoothing circuit smooths the first pulsating voltage to generate a first DC output voltage, and the first DC output A first smoothing capacitor for applying a voltage to a load; a first choke coil for storing magnetic energy due to a first pulsating voltage; and a first NMOS
A second NMOS transistor that is turned on when the transistor is turned off and supplies the electromagnetic energy stored in the choke coil to the smoothing capacitor; and the second rectifier circuit is a secondary transformer of the transformer. ON / OFF control is performed according to the voltage value of the tenth AC voltage generated in the second auxiliary winding provided on the side, and the third N that generates the second pulsating voltage.
A second smoothing capacitor having a MOS transistor, wherein the second smoothing circuit smoothes the second pulsating voltage to generate a second DC output voltage, and applies the second DC output voltage to a load. And a second choke coil for storing magnetic energy due to the second pulsating voltage, and a fourth choke coil according to the voltage value of the eleventh alternating voltage generated in the third auxiliary winding provided on the secondary side of the transformer. And a fourth NMOS transistor which is turned on when the NMOS of the second is turned off and supplies the electromagnetic energy stored in the second choke coil to the second smoothing capacitor. It is characterized in that it is inserted between the second secondary winding and the third NMOS transistor.

According to a third aspect of the present invention, a DC power source for generating a DC input voltage, and a detection circuit for detecting the voltage value of the second AC voltage generated in the first auxiliary winding forming the transformer,
The DC input voltage is ON / OFF controlled by the control signal generated by detecting the change in the voltage value of the second AC voltage,
A switching circuit that generates a first AC voltage having a predetermined frequency and a pulse width corresponding to the second AC voltage; and a change in the voltage value of the second AC voltage detected by the detection circuit,
And reset the core of the transformer by sending an exciting current to the primary winding of the transformer during the off period of the control circuit and the switching circuit that generates the control signal based on the level of the detection signal detected by the voltage change detection circuit. And a third AC voltage generated in the secondary winding due to the transformation of the first AC voltage by the transformer, on / off control based on the reset current. A mag amplifier having a reset winding for generating a fourth AC voltage having a pulse width corresponding to the reset current, a rectifying circuit for rectifying the fourth AC voltage to generate a pulsating voltage, and smoothing the pulsating voltage. Generates a DC output voltage and applies the DC output voltage to the load, and a reset current for detecting a change in the DC output voltage and negatively feedback controlling the fourth AC voltage. A voltage control circuit and a plurality of output sections each including the voltage control circuit are provided on the secondary side of the transformer, and the rectification circuit performs pulsation by performing on / off control in synchronization with the switching timing of the third AC voltage in the switching circuit. The smoothing circuit has a first NMOS transistor that generates a voltage, and the smoothing circuit smoothes the pulsating voltage to generate a DC output voltage, and a smoothing capacitor that applies the DC output voltage to a load, and electromagnetic energy due to the pulsating voltage. A mag-amplifier having a choke coil for storing and a second NMOS transistor which is turned on when the first NMOS transistor is turned off to supply the electromagnetic energy stored in the choke coil to the smoothing capacitor. Connect the gate electrode to the winding end of the secondary winding, connect the source electrode to the ground, and connect the drain electrode to the winding of the secondary winding. Connect the gate electrode of the first NMOS transistor connected to the start side, the gate electrode to the winding start side of the secondary winding, connect the source electrode to the ground side, and connect the drain electrode to the output side of the mag amp. It is characterized in that the reset current is inserted between the drain electrode and the drain electrode of the second NMOS transistor, and the reset current is input from the winding start side of the reset winding and output to the ground side.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, a voltage drop is small in a stage subsequent to the second NMOS transistor and in parallel with the second NMOS transistor. The feature is that a diode is inserted.

According to a fifth aspect of the present invention, in the invention according to any one of the first to third aspects, the active clamp circuit includes a capacitor connected to a winding end side of a primary winding of a transformer, and a control circuit. A control signal generated by the control circuit and having a phase opposite to that of the control signal is input to the gate, the output of the switching circuit is connected to the source electrode, and the drain electrode is connected to the capacitor. The output signal having a phase opposite to the control signal has a dead time so that the switching circuit and the NMOS are not turned on at the same time.

The invention according to claim 6 is the invention according to claim 1 or 3.
In the invention described, the third alternating voltage is characterized in that it has a pulse width required for the mag amplifier to saturate.

The invention described in claim 7 is characterized in that, in the invention described in claim 2, the eighth AC voltage has a pulse width necessary for saturation of the mag amplifier.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of a multi-output switching power supply circuit of the present invention will be described in detail with reference to the accompanying drawings. 1 to 7 show an embodiment of a multi-output switching power supply circuit of the present invention.

[First Embodiment] FIG. 1 shows an electrical connection configuration of a multi-output switching power supply circuit according to an embodiment of the present invention. Hereinafter, this embodiment will be described in detail with reference to FIG. The multi-output switching power supply circuit according to the present embodiment employs a forward converter, and inputs the input voltage from the DC input power supply unit 101 to the transformer 1.
The switching circuit has a switching circuit that applies a predetermined AC voltage to the main winding 121 and the auxiliary winding 122 by applying the voltage to the main winding 121 and controlling the ON / OFF of the transistor 111.
This form of multi-output switching power supply circuit is a transformer 12
On the primary side of 0, the DC power supply unit 101, the input smoothing capacitor 102, the starting resistor 103, the PWM control circuit 104,
Detection resistors 105 and 106, capacitor 107, smoothing choke coil 108, rectifying diode 109, commutation diode 110, switching circuit (for example, NM).
The OS) 111 and the active clamp circuit 112 are provided. The active clamp circuit 112 is a capacitor 1
13 and a switching NMOS 114.

The DC power supply unit 101 is composed of, for example, a battery and generates a DC input voltage V101.

The input smoothing capacitor 102 smoothes the DC input voltage V101.

The start-up resistor 103 determines the amount of start-up current to the PWM control circuit 104 by applying a voltage from the DC power supply unit at the time of start-up. After the multi-output switching power supply circuit according to the present invention is started, the PWM control circuit 104 is operated by the DC voltage generated by the auxiliary winding 122, and this DC voltage V107 (Example 2: same number, Example 3: V207). Example 4 has the same meaning as V307. See FIGS. 4, 6 and 7, respectively), which serve as a voltage supply source for the PWM control circuit.

The auxiliary winding 122 provided on the primary side of the transformer 120 has an AC voltage V122 (Embodiment 2: same number, embodiment) according to the turn ratio between the primary winding 120 and the auxiliary winding 122. 3: V222 and Example 4: V322 have the same meanings (see FIGS. 4, 6 and 7, respectively). The diode 109 rectifies this AC voltage V122, and has the same meaning as the pulsating voltage V109 (second embodiment: same number, third embodiment: V207, fourth embodiment: V309. FIGS. 4, 6, and 7 respectively). Reference) is generated.
The pulsating voltage V109 has its magnetic energy stored in the smoothing choke coil 108. The magnetic energy is supplied to the smoothing capacitor 107 when the diode 109 is off and the diode 110 is on. The pulsating voltage V109 is smoothed by the smoothing capacitor 107, and the DC voltage V107 is generated. The DC voltage V107 is divided by the resistors 105 and 106, and the change is detected by the PWM control circuit 104.
The DC voltage V107 is stabilized by the control. The DC voltage 107 also serves as a voltage supply source for the PWM control circuit 104.

The PWM control circuit 104 controls the control signal V having a predetermined frequency and a pulse width corresponding to the detected voltage detected above.
104A is generated, and the pulse width of the AC voltage V111 described later is negatively feedback controlled. Further, the PWM control circuit 104 is
The control signal V104A for controlling the NMOS 111 is generated and the control signal V104B having a phase opposite to that of the control signal is generated to control the NMOS 114.

The NMOS 111 is a PWM control circuit 104.
DC input voltage V1 based on the control signal V104A from
By controlling ON / OFF of 01, an AC voltage V1 having a predetermined frequency and a pulse width based on the detection voltage
11 is generated.

The NMOS 114 is turned on while the NMOS 111 is turned off, and a resonance circuit is formed by the primary winding 121 of the transformer 120 and the capacitor 113, so that an exciting current flows through the same primary winding 121. The core of the transformer 120 is reset.

The transformer 120 has a primary winding 12 on the primary side.
1. The auxiliary winding 122 is provided, and the secondary winding 12 is provided on the secondary side.
3, an auxiliary winding 124 for generating a control voltage V124 for controlling ON / OFF of the NMOS 132, and NM
Control voltage V12 for on / off control of OS133
It has an auxiliary winding 125 for generating 5.

On the secondary side of the transformer 120, a mag amplifier 131, synchronous rectification FETs 132 and 133, a Schottky barrier diode 134, and a smoothing choke coil 13 are provided.
5, smoothing capacitor 136, constant voltage control circuit 137,
Resistors 138, 139, transistor 140, resistor 14
1, a plurality of output sections each including a diode 142 are provided. A load RL is connected to the plurality of output units.

The mag amplifier 131 converts the AC voltage V123 output from the secondary winding 123 into a reset current I142.
(Second embodiment: same number, third embodiment: has the same meaning as I242. See FIG. 4 and FIG. 6, respectively) for on / off control and an AC voltage having a pulse width corresponding to the same reset current I142. V131 is generated.

In the NMOS 132, the gate electrode is connected to the winding end side of the auxiliary winding 124, the source electrode is connected to the output side of the mag amplifier 131, and the drain electrode is N.
It is connected to the drain electrode of the MOS 133. This NM
The OS 132 constitutes a synchronous rectification circuit, and the AC voltage V131 output from the mag amp 131 is
ON / OFF control is performed in synchronization with a change in the polarity of the AC voltage V124 output via the auxiliary winding 124, and the pulsating voltage V1
32 (same number as in the second embodiment, and has the same meaning as V242 and the like in the third embodiment. See FIGS. 4, 6 and 7, respectively).

The smoothing choke coil 135 stores the electromagnetic energy due to the pulsating voltage V132.

The NMOS 133 has a gate electrode connected to the winding start side of the auxiliary winding 125, a source electrode connected to the ground side, and a drain electrode connected to the drain electrode of the NMOS 132. This NMOS 133 is the NMOS1
When 32 is in the off state, it is in the on state and supplies the electromagnetic energy stored in the smoothing choke coil 135 to the smoothing capacitor 136.

The smoothing capacitor 136 has a pulsating voltage V1.
32 is smoothed to generate a DC output voltage V, and this DC output voltage V is applied to the load RL.

The DC output voltage V is divided by a resistor 138 and a resistor 139, and the change is divided into constant voltage control circuits 137.
Detected in.

The constant voltage control circuit 137 controls the DC output voltage V
Is detected to generate a reset current I142 for negative feedback control of the AC voltage V131.

The transistor 140 is the constant voltage control circuit 1
The current is controlled by 37, the reset current I142 is supplied from the collector of the transistor 140 via the resistor 141 and the diode 142 to the mag amplifier 131, and the AC current V131 is negatively feedback controlled. And the DC output voltage V
Is stabilized.

In this embodiment, the NMOS 133 is used.
A Schottky barrier diode 134 is connected in parallel with. This will be described with reference to FIG. The mag amplifier 131 controls the ON width by blocking the AC voltage generated in the secondary winding 123 of the transformer 120 by the reset current I142 from the constant voltage control circuit 137. However, at this time, as shown in FIG. 2, although the NMOS 132 is on, the mag-amp 13
The NMOS 133 is off during the time controlled by 1. Therefore, the load current flowing in the smoothing choke coil 135 during the time controlled by the mag amplifier 131 is
It will pass through the body diode of the NMOS 133. Since this body diode has a large voltage drop, the Schottky barrier diode 1 with a small voltage drop
34 is provided in parallel with this. By adopting such a configuration, the current of the smoothing choke coil 135 is supplied to the Schottky barrier diode 134 during the ON width control (ON cycle blocking) time by the mag amplifier 131.
To further improve the conversion efficiency.

FIG. 3 shows the waveform of each part of the multi-output switching power supply circuit of this embodiment, where the vertical axis represents voltage and the horizontal axis represents time. The operation of the multi-output switching power supply circuit of this embodiment will be described with reference to this figure. The DC power supply unit 101 generates and outputs the DC input voltage V101. The DC input voltage V101 is smoothed by the input smoothing capacitor 102. PWM control circuit 1
In 04, a control signal V104 having a predetermined frequency and a pulse width corresponding to a change in the AC voltage generated in the auxiliary winding 122.
A is generated. DC input voltage V101 is NMOS1
On / off control is performed at 11 based on the control signal V104A, and an AC voltage V111 having a predetermined frequency and a pulse width corresponding to the detection voltage of the auxiliary winding 122 is generated. This AC voltage V111 is transformed by the transformer 120, and AC voltage V123, 124, 125, is supplied to the secondary side of the transformer 120.
126 and 127 are generated.

Here, the operation of the active clamp circuit 112 for resetting the core of the transformer 120 will be described. The NMOS 111 and the NMOS 114 are complementarily turned on / off, but the timing of the control signals V104A and V104B output from the PWM control circuit 104 has a dead time so that the NMOS 111 and the NMOS 114 are not turned on at the same time. Have N
While the MOS 114 is in the ON state, the primary winding 121 of the transformer 120 and the capacitor 113 form a resonance circuit,
An exciting current flows through the same primary winding 121, and the core of the same transformer 120 is reset. Therefore, as shown in FIG. 3, the waveform of the AC voltage V111 is close to a rectangular wave, and a waveform similar to this is the waveform of the AC voltage V123. Therefore, the gate voltage of the NMOS 133 becomes an almost ideal rectangular wave, the conduction loss of the NMOS 133 is improved, and the efficiency is improved.

The AC voltage V123 appearing on the secondary side is ON / OFF controlled by the mag amplifier 131 based on the reset current I143, and an AC voltage V131 having a pulse width corresponding to the reset current I142 is generated. in this case,
Since the abrupt narrowing of the time width of the ON state of the NMOS 111 does not occur, the AC voltage V123 generated in the secondary winding 123 of the transformer 120 has a pulse width necessary for the mag amplifier 131 to be saturated. Further, the mag-amp 131 has a voltage-time product (VT product, V: mag-amp 13
The voltage applied to both ends of 1 and T: the time until the mag amplifier 131 is saturated are ensured (this will be described later in detail).

The alternating voltage V131 generated by the mag amplifier 131 changes the polarity of the alternating voltage V124 in the NMOS 132 (that is, the control voltage V124 of the NMOS 132).
ON / OFF control is performed in synchronism with (change of), and a pulsating voltage is generated. The magnetic energy of the pulsating voltage is stored in the smoothing choke coil 135. This magnetic energy is on / off controlled by the NMOS 133 in synchronization with the change of the polarity of the AC voltage V125 (that is, the change of the control voltage V125 of the NMOS 133), and when the NMOS 132 is in the off state and the NMOS 133 is in the on state. It is supplied to the smoothing capacitor 136. The pulsating voltage is
Smoothing is performed by the smoothing capacitor 136, and the DC output voltage V is generated by the smoothing capacitor 136. The DC output voltage V is applied to the load RL. DC output voltage V is
The voltage is divided by the resistors 138 and 139, and the change is detected by the constant voltage control circuit 137. Transistor 140
Current is controlled by the constant voltage control circuit 137, and the resistor 141 and the diode 14 are connected from the collector of the transistor 140.
The reset current I142 is supplied to the mag amplifier 131 via
AC voltage V123 is negatively feedback controlled. Then, the DC output voltage V is stabilized.

Here, the NMO when the load RL becomes lighter
The time width of the on state of S111 will be considered. When the load current flowing through the smoothing choke coil 135 is equal to or lower than the critical current of the smoothing choke coil 135, current flows in both directions when the NMOS 132 is in the on state as shown in FIG. It also flows in the direction.
Therefore, excess energy at the time of light load flows back through the smoothing choke coil 135 and is regenerated to the primary side via the transformer 120. Therefore, the smoothing choke coil 13
The load current flowing through 5 is continuous, and as shown in FIG.
The voltage across the smoothing choke coil 135 is [V123-V] and [-V] (where V1
23 is a transformer 12 when the NMOS 111 is in the ON state.
0, which is a voltage generated in the secondary winding 123, and V is an output voltage). Therefore, even when the load is light, the DC output voltage V does not rise, and a rapid narrowing of the time width of the ON state of the NMOS 111 does not occur.

As described above, this embodiment uses NMOS instead of the conventional rectifying and commutating diodes,
By adopting a circuit configuration that combines NMOS for synchronous rectification and constant voltage control with a mag-amplifier, heat radiation processing such as a radiator is not required, making it easy to reduce the size and efficiency of the device, and lower the voltage and increase the output. Can be planned. Further, it is possible to improve reliability by reducing internal heat generation due to the removal of the diode, which can contribute to energy saving. Further, by performing secondary side control using the mag-amplifier, it is possible to easily configure a highly stable multi-output power source with less interference between outputs.

In addition, the mag amplifier 131 is connected to the secondary winding 12
3 and the synchronous rectification NMOS 132, and the drive circuit for the synchronous rectification NMOSs 132 and 133 is configured as a separate winding from the secondary winding 123, so that synchronous rectification is performed in the loop through which the reset current flows. Is not formed, the constant voltage control by the mag amplifier 131 can be performed without being affected by the interruption of the control loop due to the turning off of the rectification side NMOS 132.

Further, by inserting the Schottky barrier diode 134 having a small voltage drop in parallel with the body diode of the NMOS 133, the mag amplifier 13
During the on-cycle blocking time by 1, the current of the smoothing choke coil 135 can be passed through this Schottky barrier diode 134, and the conversion efficiency can be improved.

Further, by inserting the active clamp circuit 112 in the primary side of the transformer 120, the NMOS
The flyback voltage when the 111 is in the off state has a waveform close to a rectangular wave, and the commutation side synchronous rectification NMOS 133 can be reliably turned on regardless of the input fluctuation and the load fluctuation. Therefore, it is possible to improve the usage efficiency of the transformer, such as being able to handle wide inputs.

As a modified example of the above-described embodiment, there is a multi-output switching power supply circuit having the configuration shown in FIG. In this embodiment, the gate voltage for controlling the NMOS 133 is not obtained from the auxiliary winding 125 of the transformer 120, but the auxiliary winding 151 is provided in the coil 150 and the winding start side of the auxiliary winding 151 is connected to the NMOS 133. It is connected to the gate electrode. Therefore, as shown in FIG. 5, an AC voltage having a phase opposite to the voltage applied to the smoothing choke coil 150 is applied to the gate electrode of the NMOS 133. Therefore, the NMOS 133, as shown in FIG. 5, during the on-cycle blocking period by the mag amplifier 131,
It is turned on by the AC voltage generated in the auxiliary winding 151. Therefore, the smoothing choke coil 150
It is possible to cause the current generated at the time to flow to the NMOS 133. Therefore, as in the first embodiment described above, the NMO
It is not necessary to provide a Schottky barrier diode in parallel with the body diode of S133. Note that V123 shown in FIG. 5 is a voltage generated in the secondary winding 123 of the transformer 120 when the NMOS 111 is in the ON state, and V is an output voltage. The voltage waveform shown in FIG. 5 illustrates the case where the winding choke coil 150 and the auxiliary winding 151 have a winding ratio of 1: 1. The voltage applied to the gate of the NMOS 133 can be freely adjusted by changing the winding ratio of the smoothing choke coil 150 and the auxiliary winding 151.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to the accompanying drawings. Referring to FIG. 6, there is shown a second embodiment according to the present invention.

The second embodiment according to the present invention is a multi-output switching power supply circuit having a main output section and a plurality of sub-output sections. The main output part is the output part of multiple systems.
It is an output unit with maximum output and little load fluctuation. Further, the duty ratio of switching on the primary side is negatively feedback controlled based on the fluctuation of the output voltage of the main output section. The output voltage of the sub-output unit other than the main output unit is feedback-controlled with an AC voltage having a duty ratio determined based on the output voltage of the main output unit.

The main output section is different from the first embodiment in that the auxiliary winding for driving and controlling the NMOSs 231 and 232 is not provided, and the mag amplifier 131 is different.
Is not provided, and the transistor 141, the resistor 142, and the diode 143 for supplying the reset current to the mag amplifier 131 are not provided.

The gate electrode of the NMOS 231 is connected to the winding end side of the secondary winding 223, the source electrode is connected to the source electrode of the NMOS 232 in the subsequent stage, and the drain electrode is connected to the winding start side of the secondary winding 223. It is connected.
The gate electrode of the NMOS 232 is connected to the secondary winding 223.
Connected to the winding start side of the
1 is connected to the source electrode, and the drain electrode is connected to the winding end side of the secondary winding 223.

The NMOS 231 constitutes a synchronous rectification circuit, and the AC voltage V223 appearing in the secondary winding is
The pulsating voltage V231 is generated by performing on / off control in synchronization with the change in the polarity of the AC voltage V223. NMOS232
Turns on when the NMOS 231 turns off and supplies the electromagnetic energy stored in the smoothing choke coil 233 to the smoothing capacitor 234.

Further, the main output section A of this embodiment is not provided with a mag amplifier and a transistor, a resistor and a diode for supplying a reset current to this mag amplifier. Therefore, the constant voltage control circuit 235 uses the smoothing coil 2
When the change in the DC output voltage V1 output from 34 is detected, the detected change in voltage is notified to the PWM control circuit 204 as a detection signal. The PWM control circuit 204 generates a control signal V204A having a pulse width based on the change of the AC voltage appearing in the auxiliary winding 222, which is proportional to the turn ratio, and the detection signal from the constant voltage control circuit 235.

The configuration of the plurality of sub-output units is the same as the configuration of the output unit of the first embodiment described above, and loads RL2 and RL3 are connected to each.

The present embodiment having such a configuration is effective when there is a large current output that cannot be controlled by the mag amplifier, and the same effects as those of the first embodiment described above can be obtained.

[Third Embodiment] Next, a third embodiment of the present invention will be described with reference to the accompanying drawings. Referring to FIG. 7, there is shown a configuration of the third exemplary embodiment according to the present invention.

The third embodiment of the present invention has the same basic configuration as that of the first embodiment described above, but the NMO
The S-synchronous rectifier circuit and the mag-amplifier control circuit are further devised.

In this embodiment, the NMOS 34 for synchronous rectification is used.
The drive voltage for controlling the driving of the motors 2, 343 is obtained from the secondary winding 323, and the mag amplifier 341 is set to N for synchronous rectification.
Gate electrode of MOS 342 (rectification side) and N for synchronous rectification
It is characterized in that it is inserted between the drain electrode of the MOS 343 (for commutation). Further, the mag amplifier 341 of the present embodiment is characterized in that a reset winding for resetting the core of the mag amplifier is separately provided. The reset current from the constant voltage control circuit 347 is input from the winding start side of the reset winding and is output from the synchronous rectification NMOS 342 to the ground side of the subsequent stage. Therefore, since the NMOS 342 for synchronous rectification is not formed in the loop through which the reset current flows, the on / off control of the mag amplifier can be performed without being affected by the interruption of the control loop due to the turning off of the rectification side NMOS 342. Voltage control becomes possible. Also,
A separate auxiliary winding is unnecessary, and the transformer can be downsized.

The above-described embodiment is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. For example, in the embodiment described above,
The synchronous rectification circuit was constructed using NMOS, but PM
It can be realized even with an OS.

[0076]

As is apparent from the above description, the present invention is an NMO instead of the conventional rectifying and commutating diodes.
By using S and using a circuit configuration that combines NMOS for synchronous rectification and constant voltage control by a mag-amplifier, heat radiation processing such as a radiator is not required, making the device compact and highly efficient, and low voltage and multiple outputs Can be easily achieved. Further, it is possible to improve reliability by reducing internal heat generation due to the removal of the diode, which can contribute to energy saving. Further, by performing secondary side control using the mag-amplifier, it is possible to easily configure a highly stable multi-output power source with less interference between outputs.

Further, the mag-amplifier is inserted between the secondary winding and the NMOS forming the rectifying circuit, and the drive circuit of the NMOS forming the rectifying circuit is an auxiliary winding different from the secondary winding. Due to the configuration, the rectifier circuit is not formed in the loop through which the reset current flows, and the constant voltage control by the mag amplifier can be performed without being affected by the interruption of the control loop due to the turning off of the rectifier side diode. .

Further, by inserting a diode having a small voltage drop in parallel with the body diode of the NMOS forming the smoothing circuit, the current of the smoothing choke coil is supplied to this diode during the on-cycle blocking time by the mag-amplifier. Sinking and conversion efficiency can be improved.

Further, by inserting the active clamp circuit on the primary side of the transformer, the flyback voltage when the switching circuit is in the off state becomes a waveform close to a rectangular wave, and the flyback voltage is surely maintained regardless of the input fluctuation and the load fluctuation. The NMOS included in the smoothing circuit can be turned on. Therefore, it is possible to improve the usage efficiency of the transformer, such as being able to handle wide inputs.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment according to the present invention.

FIG. 2 is a diagram for explaining a function of an active clamp circuit.

FIG. 3 is a signal waveform diagram of the first embodiment.

FIG. 4 is a diagram showing a configuration of a modified example of the first exemplary embodiment according to the present invention.

FIG. 5 is a signal waveform diagram of a modified example of the first embodiment.

FIG. 6 is a diagram showing a configuration of a second exemplary embodiment according to the present invention.

FIG. 7 is a diagram showing a configuration of a third exemplary embodiment according to the present invention.

FIG. 8 is a diagram showing a configuration of a conventional multi-output switching power supply circuit.

FIG. 9 is a diagram for explaining the function of the mag amplifier.

FIG. 10 is a diagram for explaining the function of a mag amplifier.

FIG. 11 is a diagram showing a configuration of a conventional multi-output switching power supply circuit.

FIG. 12 is a diagram showing a configuration of a conventional multi-output switching power supply circuit.

FIG. 13 is a diagram for explaining a problem that occurs in a conventional multi-output switching power supply circuit.

FIG. 14 is a diagram for explaining a problem that occurs in a conventional multi-output switching power supply circuit.

[Explanation of symbols]

101, 201, 301 DC power supply units 102, 201, 301 Input smoothing capacitors 103, 203, 303 Starting resistors 104, 204, 304 PWM control circuits 105, 106, 305, 306 Detection resistors 107, 205, 307 Capacitor 108 , 206, 308 Smoothing choke coils 109, 207, 309 Rectifying diodes 110, 208, 310 Commutating diodes 111, 209, 311 Switching circuits 112, 210, 312 Active clamp circuits 131, 241, 341 Mag amplifiers 132, 133 , 231, 232, 242, 243 Synchronous rectification MOSFETs 134, 345, 244 Schottky barrier diodes 135, 233, 245, 346 Smoothing choke coils 136, 234, 246, 346 Smoothing coils Capacitor 137,235,247,347 constant voltage control circuit 139,140,236,237,248,249,3
48,349 Resistors 141,250,350 Transistors 142,251,351 Resistors 143,252,352 Diodes

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 7/21

Claims (7)

(57) [Claims] 1. A DC power supply for generating a DC input voltage, a detection circuit for detecting a voltage value of a second AC voltage generated in a first auxiliary winding constituting a transformer, and a detection circuit for detecting the second AC voltage. The DC input voltage is ON / OFF controlled by a control signal generated by detecting a change in voltage value, and a first AC voltage having a predetermined frequency and a pulse width corresponding to the second AC voltage is generated. A switching circuit, a control circuit that generates the control signal based on a change in the voltage value of the second AC voltage detected by the detection circuit, and a primary winding of the transformer during an off period of the switching circuit. An active clamp circuit that resets the core of the transformer by causing an excitation current to flow is provided on the primary side of the transformer, and is generated in the secondary winding by the transformation of the first AC voltage by the transformer. A mag-amplifier that controls ON / OFF of the third AC voltage based on a reset current to generate a fourth AC voltage having a pulse width corresponding to the reset current; and a rectifier of the fourth AC voltage. A rectifying circuit that generates a pulsating voltage by means of a rectifying circuit; a smoothing circuit that smoothes the pulsating voltage to generate a DC output voltage and applies the DC output voltage to a load; A voltage control circuit that generates the reset current for controlling the negative feedback of the AC voltage of the output voltage, and a plurality of output units each of which includes a secondary side of the transformer, wherein the rectifier circuit is a secondary side of the transformer. A first NMOS transistor that is ON / OFF-controlled according to a voltage value of a fifth AC voltage generated in the second auxiliary winding provided in the first auxiliary winding, and that generates the pulsating voltage; Smoothing the A smoothing capacitor for generating a voltage and applying the DC output voltage to a load; a choke coil for storing magnetic energy due to the pulsating voltage; and a third auxiliary winding provided on the secondary side of the transformer. A second NMOS transistor that is turned on when the first NMOS is turned off according to the voltage value of the AC voltage to supply the electromagnetic energy stored in the choke coil to the smoothing capacitor; , The mag-amp with the secondary winding and the first NMO.
A multi-output switching power supply circuit characterized by being inserted between an S-transistor. 2. A DC power supply that generates a DC input voltage, a detection circuit that detects a voltage value of a second AC voltage generated in a first auxiliary winding that forms a transformer, and a detection circuit that detects the second AC voltage. The DC input voltage is ON / OFF controlled by a control signal generated by detecting a change in voltage value, and a first AC voltage having a predetermined frequency and a pulse width corresponding to the second AC voltage is generated. A switching circuit, a control circuit that generates the control signal based on a change in the voltage value of the second AC voltage detected by the detection circuit and the level of the detection signal detected by the voltage change detection circuit; An active clamp circuit that resets the core of the transformer by causing an exciting current to flow in the primary winding of the transformer during an off period of the circuit; and The by transformer of the first AC voltage by vessel 1
A rectifying circuit that rectifies a seventh AC voltage generated in the secondary winding of the first rectifying circuit to generate a first pulsating voltage, and smoothes the first pulsating voltage to generate a first DC output voltage. A first smoothing circuit that applies the first DC output voltage to a load; and a voltage change detection circuit that detects a change in the first DC output voltage to generate a detection signal and supplies the detection signal to the control circuit. And a main output section having: a second output by the transformer for transforming the first AC voltage;
A mag-amp that controls ON / OFF of an eighth AC voltage generated in the secondary winding of the second AC winding based on a reset current to generate a ninth AC voltage having a pulse width corresponding to the reset current; A second rectifier circuit that rectifies the AC voltage of to generate a second pulsating voltage; and a second DC output voltage that smooths the second pulsating voltage to generate the second DC output voltage. A second smoothing circuit applied to a load; and a voltage control circuit that detects a change in the second DC output voltage and generates the reset current for performing negative feedback control of the ninth AC voltage. A plurality of sub-output units are provided on the secondary side of the transformer, and the first rectifier circuit performs on / off control of the seventh AC voltage in synchronization with switching timing in the switching circuit. As a result, the first pulsating voltage The first of NM to generate
An OS transistor, the first smoothing circuit smooths the first pulsating voltage to generate the first DC output voltage, and applies the first DC output voltage to a load. A smoothing capacitor and a first for storing magnetic energy due to the first pulsating voltage
Second choke coil and a second NM that is turned on when the first NMOS transistor is turned off and supplies the electromagnetic energy stored in the choke coil to the smoothing capacitor.
An OS transistor, and the second rectifier circuit is ON / OFF controlled according to a voltage value of a tenth AC voltage generated in a second auxiliary winding provided on the secondary side of the transformer. ,
A second NMOS circuit for generating the second pulsating voltage, wherein the second smoothing circuit smooths the second pulsating voltage to generate the second DC output voltage; Second smoothing capacitor for applying the DC output voltage of the above to a load, and a second smoothing capacitor for storing magnetic energy due to the second pulsating voltage
And the fourth NMOS according to the voltage value of the eleventh AC voltage generated in the third auxiliary winding provided on the secondary side of the transformer.
A fourth NMOS transistor that is turned on when is turned off to supply the electromagnetic energy stored in the second choke coil to the second smoothing capacitor. A multi-output switching power supply circuit, wherein the multi-output switching power supply circuit is inserted between the second secondary winding and the third NMOS transistor. 3. A DC power supply for generating a DC input voltage, a detection circuit for detecting a voltage value of a second AC voltage generated in a first auxiliary winding constituting a transformer, and a detection circuit for detecting the second AC voltage. The DC input voltage is ON / OFF controlled by a control signal generated by detecting a change in voltage value, and a first AC voltage having a predetermined frequency and a pulse width corresponding to the second AC voltage is generated. A switching circuit, a control circuit that generates the control signal based on a change in the voltage value of the second AC voltage detected by the detection circuit and the level of the detection signal detected by the voltage change detection circuit; An active clamp circuit that resets the core of the transformer by causing an exciting current to flow in the primary winding of the transformer during an off period of the circuit; and A third AC voltage generated in the secondary winding by the transformer transforming the first AC voltage is turned on / off based on a reset current to generate a fourth AC voltage having a pulse width corresponding to the reset current. A mag amplifier having a reset winding for generating, a rectifying circuit for rectifying the fourth alternating voltage to generate a pulsating voltage, a smoothing of the pulsating voltage to generate a direct current output voltage, and the direct current output voltage The transformer includes an output unit including a smoothing circuit applied to a load, and a voltage control circuit that detects a change in the DC output voltage and generates the reset current for performing negative feedback control of the fourth AC voltage. A plurality of them on the secondary side, and the rectifying circuit generates the pulsating voltage by performing on / off control of the third AC voltage in synchronization with the switching timing in the switching circuit. A smoothing capacitor for smoothing the pulsating voltage to generate the DC output voltage and applying the DC output voltage to a load; and electromagnetic energy generated by the pulsating voltage. And a second NM which is turned on when the first NMOS transistor is turned off and supplies the electromagnetic energy stored in the choke coil to the smoothing capacitor.
And a gate electrode connected to a winding end side of the secondary winding, a source electrode connected to a ground side, and a drain electrode starting winding of the secondary winding. The gate electrode of the first NMOS transistor connected to the first side, the gate electrode to the winding start side of the secondary winding, the source electrode to the ground side, and the drain electrode to the output side of the mag amplifier. A multi-output switching power supply circuit, which is inserted between the drain electrode of a second NMOS transistor connected to the input terminal and the reset current, is input from the winding start side of the reset winding, and is output to the ground side. . 4. The diode having a small voltage drop is inserted in parallel with the second NMOS transistor after the second NMOS transistor, as claimed in any one of claims 1 to 3. Multi-output switching power supply circuit. 5. The active clamp circuit includes a capacitor connected to a winding end side of a primary winding of the transformer, and a capacitor having an opposite phase to the control signal generated by the control circuit, which is output from the control circuit. A signal having a gate input, an output of the switching circuit connected to a source electrode, and a drain electrode connected to the capacitor, and an NMOS transistor, and the control signal output from the control circuit having a phase opposite to the control signal is 4. The multi-output switching power supply circuit according to claim 1, wherein a dead time is provided so that the switching circuit and the NMOS are not turned on at the same time. 6. The multi-output switching power supply circuit according to claim 1, wherein the third AC voltage has a pulse width required for saturating the mag amplifier. 7. The multi-output switching power supply circuit according to claim 2, wherein the eighth AC voltage has a pulse width required for saturating the mag amplifier.