JPH079588Y2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a switching power supply device used as a stabilized DC power supply.

[Prior Art] As a switching power supply device of this type, lightweight, small size,
The RCC (ringing choke converter) type has been widely used since it is inexpensive and highly efficient.

A conventional RCC type switching power supply device is an output circuit that extracts a DC voltage to the secondary side of a transformer whose primary side is connected to a DC power supply via a switching transistor that forms a switching unit, and an output detection that detects the DC voltage. A bypass transistor is connected to the circuit and bypasses the base current of the switching transistor according to the magnitude of the output voltage in response to the detection signal from the phototransistor (light receiving element) of the output detection circuit. This is a self-excited DC-DC converter circuit that mainly consists of a ringing choke converter.

In the switching power supply device of the RCC method with the above configuration, the phototransistor and the bypass transistor are operated according to the magnitude of the DC voltage extracted from the output circuit connected to the secondary side of the transformer, and the base current of the switching transistor is changed. Adjust it to change its on period,
Therefore, it operates so as to stabilize the output DC voltage regardless of load fluctuations.

By the way, in the switching power supply device configured as described above, when the switching transistor is switched from the on state to the off state, the bypass transistor gradually sweeps the base current of the switching transistor, so that the switching transistor does not turn off promptly. As a result, switching loss is large, which has been a major obstacle to improving efficiency.

In order to reduce the switching loss in such a switching unit, the applicant of the present application has previously proposed a switching power supply device as disclosed in Japanese Patent Application Laid-Open No. 2-131363.

FIG. 5 is a circuit configuration diagram of the switching power supply device previously proposed by the applicant of the present application.

In the figure, 10 is a ringing choke converter,
The DC voltage a generated by a rectifier circuit (not shown) is supplied. The ringing choke converter 10 includes an electric field capacitor 11, a switching transistor 12 (switching unit), a converter transformer 14, a rectifier circuit (output circuit).
It is composed of 15 etc., and when the DC voltage a is energized,
The switching transformer 12 is connected via the starting resistor 13 on the N1 winding side of the converter transformer 14 and the base resistor 16 on the N2 winding side.
Although a base current flows through the switch, it is quickly turned on, but the primary side current c that is the control symmetry of the switching transistor 12 does not rise instantaneously due to the inductance of the converter transformer 14 and increases like a ramp function.

At the same time that the switching transistor 12 is turned on, the positive base current generated on the N2 winding side of the converter transformer 14 flows, while when the primary side current c becomes large to some extent, the switching transistor 12 is turned on due to the characteristics of the transistor. Switch from state to off state.

When the switching transistor 12 is turned off,
The energy accumulated in the converter transformer 14 is released to the rectifier circuit 15 side, and at the timing when this energy release is completed, the switching transistor 12 is again in the forward bias state and switched to the on state, and thereafter, the same operation is repeated. Therefore, the switching transistor 12 is switched.

More specifically, the switching transistor 12
Is a switching element for controlling the primary side current c of the converter transformer 14, and is controlled by the same principle as the above although the ON period is regulated by the control circuit 50 described later.

In this switching process, the energy supplied from the primary side is stored in the converter transformer 14 in the half cycle in which the switching transistor 12 is in the ON state, while it is stored in the converter transformer 14 in the subsequent half cycle in the OFF state. Energy is transferred to the electrolytic capacitor 152 in the rectifier circuit 15, whereby a DC voltage b is generated across the electrolytic capacitor 152.

The rectifier circuit 15 is connected to the N3 winding on the secondary side of the converter transformer 14 as described above, and the primary side current sensing circuit described later is connected to the N2 winding.
30 is connected. The secondary coil voltage e generated in the N2 winding is (N2 / N1) times the primary voltage h supplied to the N1 winding because of the winding ratio.

An output detection circuit which is connected to the output stage of the ringing choke converter 10 having the above-mentioned configuration and detects the DC voltage b
20 is a circuit including a resistor 21, a resistor 22, a shunt regulator 23, a photodiode (light emitting element) 24, and the like,
The shunt regulator 23, which uses the divided voltage obtained by dividing the force current voltage b by the resistor 21 and the resistor 22 as the bias voltage, controls the current, and operates the photodiode 24 by the controlled current to increase the magnitude of the DC voltage b. It is configured to detect the height.

Reference numeral 40 denotes a voltage control signal generation circuit. The voltage control signal generation circuit 40 has a phototransistor (light receiving element) 46 that receives a detection signal from the photodiode 24 of the output detection circuit 20, and the detection from the photodiode 24 is performed. Upon receiving the signal, the voltage control signal d corresponding to the DC output voltage b is output. However, this voltage control signal d is a signal that rises when the DC output voltage b falls, and its maximum value is increased by the reference voltage d1 generated by the reference voltage generation circuit including the resistors 42, 43, 44 and the Zener diode 45. Is regulated.

The primary side current sensing circuit 30 includes a resistor 311 and a capacitor 312, an integrating circuit 31 for integrating the secondary side coil voltage e, a transistor 321 and a diode 322, and a reset for discharging the charge of the capacitor 312. The circuit 32 is configured to generate an equivalent signal f having the same waveform as the primary current c. That is, the primary side current c flowing through the ringing choke converter 10 is not directly detected, but an equivalent signal f is generated by using the secondary side coil voltage e as an input, and the primary side current c is indirectly detected. .

Reference numeral 41 denotes an IC comparator, which compares the equivalent signal f and the voltage control signal d in voltage and opens / closes a bypass transistor 51 (switching element) for controlling the switching transistor 12 based on the voltage comparison result. Has become. More specifically, the comparator
The positive side input of 41 is connected to the output stage of the primary side current sensing circuit 30, while the negative side input is connected to the resistor 42 to the phototransistor 46 which is the output stage of the output detection circuit 20. A reference voltage generation circuit composed of 44 and Zener diode 45 is connected.

The control signal g which is the output signal of the comparator 41 is guided to the control circuit 50.

The control circuit 50 is a switching circuit mainly composed of a bypass transistor 51 that operates according to the control signal g generated by the comparator 41, and includes a N2 winding of the converter transformer 14 and a base resistor 16
The base power supply k that flows through the circuit is bypassed, and the on-time of the switching transistor 12 is made variable by this. The control signal g is
It is pulled up by the secondary voltage e via the resistor 52 and the diode 53, and the diode 53 is a protection diode when the transistor 51 is in the reverse bias state.

Next, the operation of the switching power supply device configured as described above will be described with reference to the timing chart of FIG.

First, in the period T0, the normal-side primary current c commensurate with the size of the load is flowing, and the control signal generated by the comparator 41 is generated at the timing when the equivalent signal f becomes larger than the voltage control signal d. The signal g becomes active, the bypass transistor 51 is turned on, and the ON period of the switching transistor 12 is regulated, whereby the maximum level of the primary side current c is regulated, whereby the DC output voltage b is stabilized at a constant level. To be done.

Further, in the period T1, if the load state changes and becomes a form close to a short circuit, the DC output voltage b becomes nearly zero, and the primary side current c becomes abnormally large, the voltage decreases as the DC output voltage b decreases. Although the control signal d tends to rise, its maximum value is regulated by the reference voltage d1 and saturated, while the equivalent signal f becomes even larger. This equivalent signal f
The control signal g becomes active and the switching transistor 12 is forcibly turned off at the timing when the voltage becomes higher than the reference voltage d1, that is, at time t1. In other words, the maximum level of the voltage control signal d is limited to a value commensurate with the magnitude of the reference voltage d1 even if the DC output voltage b decreases and the primary current c increases due to a short circuit on the load side. The switching transistor 12 and the like are protected from overcurrent. That is, the reference voltage generating circuit including the Zener diode 45, the resistors 43 and 44, etc. is a circuit necessary for determining the maximum allowable level of the primary side current c.

After that, when the load condition is restored in period T2,
The same control as that of T0 is performed, but if the load state becomes lighter over the period T3, the DC output voltage b rises and the voltage control signal d drops accordingly. In other words, the comparator 41 compares the equivalent signal f with the output voltage b. The threshold value is considerably lowered, and the on time of the switching transistor 12 is shortened. This tends to reduce the DC output voltage b, and as a result, even if the load condition changes, the DC voltage b
Will be promptly restored.

Here, the control operation of the comparator 41 that turns on and off the switching transistor 12 will be described in detail.

The comparator 41 compares the equivalent signal f output from the primary side current sensing circuit 30 with the voltage control signal d that changes according to the fluctuation of the output voltage b on the secondary side, and f> d
At the time of, the comparator 41 outputs a high-level control signal g to turn on the bypass transistor 51 and turn off the switching transistor 12 to reduce the output voltage b. When f <d, the comparator 41 goes low. A level control signal g is output to turn off the bypass transistor 51, maintain the switching transistor 12 in the on state, and increase the output voltage b.

Then, the waveform of the above-mentioned equivalent signal f shows that the rectangular side secondary coil voltage e applied to the integrating circuit 31 charges the capacitor through the resistor 311 and the diode 322, and the subsequent operation of the transistor 321 causes A triangular wave as shown in Fig. 7 is obtained, and when the load on the output side becomes light or there is no load, the voltage becomes almost 0 V when the transistor 321 is turned on. On the other hand, the voltage control signal d indicates that the load on the output side is reduced, that is, the output voltage b.
Although it approaches 0V with the rise of, the voltage cannot be lowered to the saturation voltage (0.6 to 0.7V) of the phototransistor 46 or less, and the equivalent signal f of the level below the saturation voltage does not fall within the controllable range of the comparator 41. , This comparator
You lose control of 41, and as a result
As indicated by the dotted line X in the output characteristic of FIG. 3, the output voltage b rises above the set value.

[Problems to be Solved by the Invention] As described above, in the case of the switching power supply device previously proposed by the applicant of the present application, switching operation is performed by controlling the switching operation of the switching transistor 12 through the comparator 41 and the control circuit 50. Although it is possible to speed up the turn-off of the transistor 12 and reduce the switching loss, when the load on the output side becomes lighter than a predetermined value, the output voltage rises and the output voltage is controlled to the set value. There is a problem that the possible load range is limited to the range of A in FIG. 3, and as a countermeasure for that, a dummy load or the like is required on the secondary side, and it is necessary to increase the rating of the element.

The present invention has been made in view of the above circumstances, and it is possible to stably control the output voltage to a predetermined value and expand the dynamic range until the load on the output side becomes unloaded without requiring a dummy load or the like. An object of the present invention is to provide a switching power supply device that can be used.

[Means for Solving the Problems] In order to achieve the above object, a switching power supply device according to the present invention includes a switching unit, a transformer whose primary side is connected to a DC power supply through the switching unit, and An output circuit for extracting a DC output from the secondary side, an output detection circuit for detecting the DC output, and a light receiving element, and receiving a detection signal from the light emitting element of the output detection circuit, a voltage corresponding to the output voltage. A voltage control signal generation circuit that outputs a control signal, a primary side current sensing circuit that generates an equivalent signal having the same waveform as the primary side current based on the primary side or secondary side coil voltage of the transformer, and the voltage control signal And a comparator for comparing the equivalent signal, and has a switching element for controlling the switching unit, the comparison result of the comparator And a bias circuit that lowers the level of the voltage control signal by a level substantially equal to the saturation voltage of the light receiving element. It will be done.

[Operation] According to this invention, the equivalent signal generated by the primary side current sensing circuit is input to one of the comparators, and the voltage control signal output corresponding to the output voltage is input to the other of the comparators. By comparing these two signals and changing the ON time of the switching unit by opening and closing the switching element based on the comparison result, the DC output taken out from the output circuit is controlled to the set value regardless of the load fluctuation. Here, a bias means is added between the light receiving element and the ground in the voltage control signal generating circuit, and the level of the voltage control signal is lowered by a level approximately equal to the saturation voltage of the light receiving element, thereby reducing the load on the output side. Even when the load becomes lighter or there is no load, the DC output can be stably controlled to a predetermined value without sufficiently increasing the output voltage by controlling the comparator.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit configuration diagram of a switching power supply device according to the present invention. In FIG. 1, the point different from the conventional example shown in FIG. 5 is that a phototransistor (light receiving element) 46 in a voltage control signal generation circuit 40. A negative voltage bias circuit (bias means) 60 is added between the ground and the ground to adjust the level of the voltage control signal d to the saturation voltage (usually 0.6) of the phototransistor (light receiving element) 46 in the voltage control signal generation circuit 40.
~ 0.7V) is a point that is configured to drop by a level approximately equal to.

The negative voltage bias circuit 60 includes a resistor 611 and a diode 61.
It is composed of 2,613 and a capacitor 614, and biases the phototransistor 46 to a negative potential. Since the other configurations are the same as those of the conventional example shown in FIG. 5, the same reference numerals are given to the corresponding portions, and the description thereof will be omitted.

Next, the operation of the switching power supply device having the above configuration will be described. The operation when the load on the output side is equal to or greater than the predetermined value is the same as that of the conventional example, and therefore the description is omitted. Here, when the load on the output side is equal to or less than the predetermined value, the added negative voltage bias circuit is added. Only the control operation of 60 and the comparator 41 will be described.

That is, when the rectangular coil secondary side coil voltage as shown in FIG. 2e is applied from the N2 winding of the converter transformer 14 to the negative voltage bias circuit 60, the rectangular wave secondary side coil voltage e is The voltage waveform is limited by 611 and becomes a voltage waveform as shown in FIG. Next, after passing through the diode 612 and rectifying only its negative potential as shown in FIG. 2j, it is smoothed by the capacitor 614 and becomes a continuous negative potential as shown in FIG. 2m. In addition, here, the diode 61
As shown in FIG. 2n, the excessive negative potential is cut off by 3, so that the negative potential j is controlled to a negative bias lower than the ground potential (0V) by the forward voltage −Vf of the diode 613. And always creates a stable negative potential bias voltage.

By applying the bias voltage of the negative potential as described above to the phototransistor 46, the level of the voltage control signal d input to the comparator 41 is set to the saturation voltage of the phototransistor 46 as shown in FIG. Is lowered by a level ΔL substantially equal to

As a result, even when the load on the output side is from a predetermined value or less to no load, as shown by the solid line Y in the output characteristic diagram of FIG. 4, the DC output voltage b is increased to the predetermined value without increasing. It is possible to perform stable and good control. That is, it is possible to expand the load range in which the switching power supply device can be used as a stabilized DC power supply.

[Effect of the Invention] As described above, according to the present invention, the switching operation of the switching unit is controlled through the comparator and the control circuit, thereby quickly turning off the switching unit and reducing the switching loss.
Not only can the overall efficiency be improved, but the output voltage can be stabilized at the set value until the load on the output side becomes unloaded simply by adding biasing means that can be configured from minute power components with few points. The power supply can be controlled and can be effectively used even for a power supply having a wide load range without requiring a dummy load or the like, and the dynamic range can be expanded.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a switching power supply device according to the present invention, FIGS. 2 and 3 are signal waveform diagrams for explaining the operation of the main part, FIG. 4 is an output characteristic diagram,
FIG. 5 is a circuit configuration diagram of a conventional switching power supply device, FIG. 6 is a timing chart showing a signal waveform for explaining the operation of the conventional switching power supply device, and FIG. 7 is a signal of a main part for explaining the operation of the conventional example. It is a waveform diagram. 12 ... Switching transistor (switching part), 14
... Transformer, 15 ... Rectifier circuit (output circuit), 20 ... Output detection circuit, 24 ... Photodiode (light emitting element), 30 ... Primary side current sensing circuit, 40 ... Voltage control signal generation circuit, 41 ...
Comparator, 46 ... Phototransistor (light receiving element),
50 ... Control circuit, 60 ... Negative voltage bias circuit (biasing means), 611 ... Resistor, 612,613 ... Diode, a, b ...
DC voltage, d ... Voltage control signal, f ... Equivalent signal, g ... Control signal.

Claims (1)

[Scope of utility model registration request] 1. A switching unit, a transformer whose primary side is connected to a DC power source via the switching unit, and an output circuit for extracting a DC output from the secondary side of the transformer.
An output detection circuit that detects the DC output, a voltage control signal generation circuit that has a light receiving element, receives a detection signal from the light emitting element of the output detection circuit, and outputs a voltage control signal corresponding to the output voltage, A primary side current sensing circuit that generates an equivalent signal having the same waveform as the primary side current based on the primary side or secondary side coil voltage of the transformer, a comparator that compares the voltage control signal and the equivalent signal,
A control circuit that has a switching element that controls the switching section, and that opens and closes the switching element based on the comparison result of the comparator to change the ON time of the switching section, and the level of the voltage control signal. And a bias means for lowering the voltage by a level substantially equal to the saturation voltage of the light receiving element.