JP3377128B2 - Switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention switches a main switching element in response to a drive signal from a control circuit to intermittently apply a DC input voltage to a primary winding of a main transformer. The present invention relates to an applied switching power supply device. 2. Description of the Related Art In general, this type of switching power supply device intermittently applies a DC input voltage to a primary winding of a main transformer by switching a main switching element by a drive signal from a control circuit. And the power is supplied from the secondary winding of the main transformer to the output side.
A predetermined operating voltage must be supplied to a control circuit, an operational amplifier forming a feedback loop, and the like. To this end, an auxiliary power supply circuit is provided in the device separately from the main inverter. [0003] As an auxiliary power supply circuit in the above-mentioned prior art, there is known an auxiliary power supply circuit for reducing a DC input voltage to a predetermined operation voltage by using a voltage dividing resistor or a dropper, for example. However, when the operating voltage of the control circuit is higher than the DC input voltage, such a method cannot be applied. On the other hand, a method of extracting an operating voltage higher than the DC input voltage using a booster type auxiliary power supply circuit is also known, but in particular, a control IC using various protection circuits and the like is used as a control circuit. In this case, there is a problem that an operating voltage higher than the starting voltage of the control circuit is supplied from the auxiliary power supply circuit even in a steady state, and the loss of the control circuit increases. [0004] The present invention has been made in view of the above problems, it is possible to reduce the loss to the control circuit, the existing auxiliary power times
For roads, easily reduce loss to control circuits
It is an object of the present invention to provide a switching power supply device capable of performing such operations. A switching power supply according to the present invention supplies a main switching element for intermittently applying a DC input voltage to a primary winding of a main transformer, and supplies a drive signal to the main switching element. A switching power supply device having an auxiliary power supply circuit for supplying a predetermined operating voltage to the control circuit, wherein an operation output terminal for notifying an operation state of the control circuit is provided in the control circuit, An operation voltage switching circuit for switching the operation voltage based on a control signal from the operation output terminal is provided in the auxiliary power supply circuit, and the auxiliary power supply circuit includes a transformer for converting the DC input voltage to the operation voltage and a transistor. A control voltage source for controlling a base current of the transistor; When a shall such from the control voltage switching means for switching based on a control voltage from the control voltage source to the control signal from the operation output terminal. With the above arrangement, the auxiliary power supply circuit first supplies the control circuit with an operating voltage at which the control circuit can be started. Thereafter, when a control signal indicating that the control circuit has been operated is applied from the operation output terminal to the operation voltage switching means, the operation voltage switching means switches the operation voltage to the control circuit to a voltage value lower than that at the time of startup. A self-excited converter having the simplest circuit configuration
Control circuit using an auxiliary power circuit
The operating voltage can be switched, and the existing auxiliary power supply circuit
On the other hand, easily reduce the loss to the control circuit
Becomes possible. Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a first embodiment of the present invention, in which 1 is a main transformer for insulating a primary side from a secondary side,
Reference numeral 2 denotes an NPN which is a main switching element constituting a main inverter 3 by a series circuit with the primary winding 1A of the main transformer 1.
Type transistor, and the DC input voltage Vi is applied to the primary winding 1A of the main transformer 1 by switching of the transistor 2.
Is applied intermittently. Reference numeral 4 denotes a control IC as a control circuit for supplying a drive signal from the drive terminal D to the base of the transistor 2, and is activated when a predetermined operation voltage Vc is applied between the operation voltage input terminal Vcc and the ground terminal G. It is supposed to. On the other hand, on the secondary winding 1B side of the main transformer 1, a rectifying diode 6, a flywheel diode 7, a choke coil 8,
And a smoothing capacitor 9 are connected. Then, the voltage induced in the secondary winding 1B of the transformer 1 in accordance with the switching of the transistor 2 is rectified and smoothed by the rectifying and smoothing circuit 5, and is supplied as a DC output voltage Vo to a load (not shown). Reference numeral 11 denotes an auxiliary power supply circuit for supplying a predetermined operating voltage Vc to the control IC 4. This auxiliary power circuit
Reference numeral 11 denotes a self-excited flyback converter having a simple circuit configuration for converting the DC input voltage Vi into the operating voltages Vc and Vd, and is provided separately from the main transformer 1.
And an NPN transistor 13 which is a switching element connected to the primary winding 12A of the transformer 12.
A series circuit of a Zener diode 14 and a resistor 15 is connected between the primary winding 12A of the transformer 12 and the base of the transistor 13, and a grounded NPN transistor is connected between the base and the emitter of the transistor 13.
A collector 17 and a base 16 are connected to each other, and a resistor 17 is connected between the base and the emitter of the transistor 16. The transformer 12 has two secondary windings 12B and 12C, and one of the secondary windings 12B is connected to the operating voltage input terminal Vcc of the control IC 4 via a rectifier diode 18 and a smoothing capacitor 19 and to ground. The other secondary winding 12C is connected to a terminal G via a rectifier diode 20 and a smoothing capacitor 25 to an operational amplifier (not shown) in a power supply device operating at a different operation voltage Vd. The control IC 4 is provided with an operation output terminal OUT for notifying the operation state.
When C4 rises, an H level control signal is output to the operation output terminal O
The data is output from the UT. This control IC
4 between the operation output terminal OUT and the secondary winding 12B of the transformer 12, the operation voltage V supplied from the auxiliary power supply circuit 11 to the control IC 4 based on the control signal from the operation output terminal OUT.
An operating voltage switching circuit 21 for switching the value of c is provided. The operating voltage switching circuit 21 includes a series circuit of zener diodes 22, 23 as a control voltage generating source connected between the operating voltage input terminal Vcc line and the base of the transistor 16,
The drain and source are connected to both ends of one Zener diode 23, and the MOSFET is configured as a control voltage switching means having a gate connected to the operation output terminal OUT. The operation output terminal OU of the control IC 4
As T, any terminal may be used as long as at least a signal such as a feedback terminal or a reference voltage monitoring terminal is output when the control IC 4 rises. In this embodiment, for example, a drive signal from the drive terminal D can be used as it is as a control signal. In this case, the drive signal in the form of a pulse wave may be rectified and smoothed by a rectifying and smoothing circuit including a diode and a capacitor, and then applied to the gate of the FET 24. Next, the operation of the above configuration will be described. When a DC input voltage Vi is applied to the power supply device shown in FIG. 1, a current generated in the starting resistor 15 flows through the Zener diode 14 on the auxiliary power supply circuit 11 side to the base of the transistor 13, and the transistor 13 is turned on. At this time, the DC input voltage Vi is applied to the primary winding 12A of the transformer 12.
Is applied, the voltage induced in the secondary windings 12B and 12C is applied to the diodes 18 and 20 in the opposite direction, and the secondary winding 12B and Since no current flows from 12C, the exciting current of the transformer 12 which increases linearly with time flows through the primary winding 12A, and the operating point of the transistor 13 shifts from the saturation region to the active region. When the transistor 13 is turned off with an increase in the collector-emitter voltage of the transistor 13, the diodes 18 and 20 conduct, and the energy stored in the transformer 12 is transferred to the secondary winding.
It is supplied to the output side from 12B and 12C. As a result, DC operating voltages Vc and Vd are generated on the secondary windings 12B and 12C side of the transformer 12, respectively. In the auxiliary power supply circuit 11, a control IC
At the time of start-up until the rising edge of the operation voltage switch 4, the operation output terminal OUT is at the L level.
T24 is turned off. In this case, a Zener diode
The zener voltages which are the control voltages of 22, 23 are respectively VZ1, VZ
2, the base potential of the transistor 16 becomes Vc-
(VZ1 + VZ2). On the other hand, control I
When C4 rises and an H-level control signal is supplied from the operation output terminal OUT to the gate of the FET 24, the FET 24 turns on, and both ends of the Zener diode 23 are short-circuited.
The base potential of the transistor 16 rises to Vc-VZ1, and the current flowing between the collector and the emitter of the transistor 16 increases. Then, the current flowing to the base of the transistor 13 decreases as the base potential of the transistor 16 increases, and as a result, the ON period of the transistor 13 is shortened. A lower operating voltage Vc is supplied to the control IC 4. Thereafter, in a steady state, a drive signal having a pulse conduction width corresponding to the output voltage Vo is supplied from the control IC 4 to the transistor 2 of the main inverter 3.
Due to the switching of the transistor 2, the DC input voltage Vi is intermittently applied to the primary winding 1A of the main transformer 1, and a stable DC output voltage Vo is supplied from the secondary winding 1B via the rectifying and smoothing circuit 5. You. As described above, according to the above-described embodiment, the transistor 2 for intermittently applying the DC input voltage Vi to the primary winding 1A of the main transformer 1, and the driving of the transistor 2 And a control IC 4 for supplying a signal, and an auxiliary output circuit 11 for supplying a predetermined operating voltage Vc to the control IC 4. In a switching power supply device, an operation output terminal O for notifying an operation state of the control IC 4 is provided.
A UT is provided on the control IC 4 and an operation output terminal O
The auxiliary power supply circuit 11 is provided with an operating voltage switching circuit 21 for switching the operating voltage Vc based on a control signal from the UT. In this case, the operating voltage Vc higher than the starting voltage is first supplied from the auxiliary power supply circuit 11 to the control IC 4, and then a control signal indicating that the control IC 4 has risen is sent from the operation output terminal OUT to the operating voltage switching means 21. Is applied, the operating voltage switching means 21 switches the operating voltage Vc to the control IC 4 to a voltage value lower than the starting voltage at which the control IC 4 can operate, so that the operating voltage Vc of the control IC 4 is changed to the DC input voltage. Even when it is higher than Vi, it is possible to reduce the loss of the control IC 4 due to the high operating voltage Vc in the steady state. Further, in this embodiment, the self-exciting converter that includes a transformer 12 and a transistor 13 for converting the direct inflow power voltage Vi to the operating voltage Vc constitutes an auxiliary power supply circuit 11, controls the base current of the transistor 13 By configuring the operating voltage switching circuit 21 with the Zener diodes 22 and 23 and the MOSFET 24 that switches the Zener voltages VZ1 and VZ2 from the Zener diodes 22 and 23 based on the control signal from the operation output terminal OUT, The operating voltage Vc for the control IC 4 can be switched using the auxiliary power supply circuit 11 composed of a self-excited converter having a simple circuit configuration, and the loss for the control IC 4 can be easily reduced even for the existing auxiliary power supply circuit 11. It becomes possible to reduce. In the embodiment, the output voltage Vo is obtained by the forward converter, but the present invention can be applied to a flyback converter or other push-pull converters. Further, the main switching element is not limited to a transistor, and a MOS FET or the like may be used. Next, a second embodiment of the present invention will be described with reference to FIG. The parts common to the first embodiment are denoted by the same reference numerals, and the detailed description of the common parts is omitted. In the figure, reference numeral 31 denotes an operating voltage switching circuit for switching the value of the operating voltage Vc supplied to the control IC 4. In this embodiment, a shunt regulator 32 is provided as a control voltage generating source instead of a Zener diode. The control voltage switching means 33 for switching the control voltage includes an NPN transistor 34 having a base connected to the operation output terminal OUT, and resistors 35 and 36 between the operation voltage input terminal Vcc line and the collector of the transistor 34. A PNP transistor 37 whose base is connected to the connection point. The emitter of the transistor 34 is connected to the ground terminal G line, and the emitter of the transistor 37 is connected to the resistor 38.
Is connected to the operating voltage input terminal Vcc line via
A series circuit of resistors 39 and 40 is connected between the operating voltage input terminal Vcc line and the ground terminal G line, and the connection point of the resistors 39 and 40 connects the reference of the shunt regulator 32 and the collector of the transistor 37. Is connected.
The anode of the shunt regulator 32 is connected to the ground terminal G line, and the cathode is connected to the operating voltage input terminal Vcc line via the resistor 41. The base of a PNP transistor 42 is connected to the connection point between the resistor 41 and the shunt regulator 32. The emitter of the transistor 42 is connected to the operating voltage input terminal Vcc line, and the collector is connected to the base of the transistor 16. The other is the first
It has the same configuration as the switching power supply device shown in the embodiment. In the above configuration, at the time of startup until the control IC 4 rises, the operation output terminal OUT is at the L level, the transistors 34 and 37 are both turned off, and the operation voltage Vc is changed to the resistances 39 and 40. The operating voltage Vc is controlled such that the voltage divided by the above becomes equal to the reference voltage of the shunt regulator 32. On the other hand, the control I
When C4 rises and an H-level control signal is supplied from the operation output terminal OUT to the base of the transistor 34, both of the transistors 34 and 37 are turned on. The operating voltage Vc is controlled so that the compressed voltage becomes equal to the reference voltage of the shunt regulator 32. The operating voltage Vc at this time is lower than when the operation output terminal OUT is at the L level. On the other hand, the base current of the transistor 42 increases compared to when the output terminal OUT is at the L level. Then, the base potential of the transistor 16 rises, and the on-period of the transistor 13 is shortened in the same manner as in the first embodiment. Vc is supplied to the control IC 4. In this embodiment, a transistor 2 for intermittently applying a DC input voltage Vi to a primary winding 1A of a main transformer 1 and a control for supplying a drive signal to the transistor 2 are provided. In the switching power supply device having an IC 4 and an auxiliary power supply circuit 11 for supplying a predetermined operating voltage Vc to the control IC 4, an operation output terminal OUT for notifying an operation state of the control IC 4 is provided in the control IC 4. Operating voltage switching circuit 31 for switching the operating voltage Vc based on a control signal from an operation output terminal OUT.
Is provided in the auxiliary power supply circuit 11, so that the control IC
Even when the operating voltage Vc is higher than the DC input voltage Vi, it is possible to reduce the loss of the control IC 4 due to the high operating voltage Vc in the steady state. Further, in this embodiment, the self-exciting converter that includes a transformer 12 and a transistor 13 for converting the direct inflow power voltage Vi to the operating voltage Vc constitutes an auxiliary power supply circuit 11, controls the base current of the transistor 13 The shunt regulator 32 and the control voltage switching means 33 for switching the control voltage from the shunt regulator 32 based on the control signal from the operation output terminal OUT constitute the operating voltage switching circuit 31, so that the existing auxiliary power supply circuit 11 On the other hand, it is possible to easily reduce the loss to the control IC 4. FIG. 3 shows a third embodiment of the present invention. The difference from the second embodiment is that a resistor 35 and a resistor 35 are connected between the operating voltage input terminal Vcc line and the ground terminal G line.
36 series circuits are connected, and the connection point of these resistors 35 and 36 is
The point where the collector of the transistor 34 is connected to the base of the NPN transistor 37, the emitter of the transistor 37 is connected to the ground terminal G line, and the collector is connected via the resistor 38 to the connection point of the resistors 39 and 40. Is that
The other parts have the same configuration as the second embodiment. When the control IC 4 whose operation output terminal OUT is at the L level is activated, the transistor 34
Is turned off, the transistor 37 is turned on, and the operating voltage Vc is controlled so that the voltage divided by the resistor 39 and the parallel circuit of the resistors 38 and 40 becomes equal to the reference voltage of the shunt regulator 32. I do. On the other hand, when the H-level control signal is output from the operation output terminal OUT, the transistor 34 is turned on, the both ends of the resistor 36 are short-circuited, and no current flows into the base of the transistor 37, and the transistor 37 is turned off. Is turned off. Therefore, this time, the operating voltage Vc is controlled so that the voltage divided by the resistors 39 and 40 becomes equal to the reference voltage of the shunt regulator 32, the current flowing into the cathode of the shunt regulator 32 increases, and the transistor The base potential of 16 rises. And the control I
After the rise of C4, the operating voltage Vc is lower than that at the time of startup.
Is supplied to the control IC 4 and operates in the same manner as in the second embodiment.
It will be effective. The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. According to the first aspect of the present invention, there is provided a switching power supply device for supplying a main switching element for intermittently applying a DC input voltage to a primary winding of a main transformer, and supplying a drive signal to the main switching element. A switching power supply device having an auxiliary power supply circuit for supplying a predetermined operating voltage to the control circuit, wherein an operation output terminal for notifying an operation state of the control circuit is provided in the control circuit, An operation voltage switching circuit for switching the operation voltage based on a control signal from an operation output terminal is provided in the auxiliary power supply circuit, and the auxiliary power supply circuit changes the DC input voltage to the operation voltage.
Self-contained with a transformer and a transistor for converting the operating voltage
And the operating voltage switching circuit is
Control voltage source for controlling transistor base current
And the control voltage from this control voltage source
Control voltage switching means for switching based on a control signal from a terminal
And is made of, it is possible to reduce the loss to the control circuit by high operating voltages, also to existing auxiliary power supply circuit, it is possible to easily reduce the loss to the control circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram of a switching power supply device showing a first embodiment of the present invention. FIG. 2 is a circuit diagram of a main part showing a second embodiment of the present invention. FIG. 3 is a circuit diagram of a main part showing a third embodiment of the present invention. [Description of Signs] 1 Main transformer 2 Transistor (main switching element) 4 Control IC (control circuit) 11 Auxiliary power supply circuit 12 Transformer 13 Transistor (switching element) 21, 31 Operating voltage switching circuit 22, 23 Zener diode (Control voltage) Source) 24 MOS FET (Control voltage switching means) 32 Shunt regulator (Control voltage source) OUT Operation output terminal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI H02M 3/338 H02M 3/338 A

Claims (1)

(1) A main switching element for intermittently applying a DC input voltage to a primary winding of a main transformer, and a control circuit for supplying a drive signal to the main switching element. A switching power supply device having an auxiliary power supply circuit for supplying a predetermined operating voltage to the control circuit, wherein an operation output terminal for notifying an operation state of the control circuit is provided in the control circuit; An operation voltage switching circuit for switching the operation voltage based on a control signal is provided in the auxiliary power supply circuit, and the auxiliary power supply circuit is connected to the DC input power supply.
Transformer and a transistor for converting the voltage to the operating voltage.
A self-excited converter with
A circuit for controlling a base current of the transistor;
And a control voltage from the control voltage source.
Control voltage that switches based on the control signal from the operation output terminal
Switching power supply apparatus characterized by comprising a switching means.