JP3019093B1 - Switching power supply - Google Patents

Abstract

A switching device does not provide stable intermittent oscillation operation without magnetostrictive noise. A series circuit of a main switch and a primary winding of a transformer is connected to a DC power supply. Set main switch 4 to P
On / off control is performed by the WM pulse. Detect output voltage,
A current corresponding to this is passed through the light emitting diode 24. At the time of standby, the current If is forced to flow through the light emitting diode 24. A capacitor 31 is provided for a bias power supply of the phototransistor 39. The capacitor 31 is charged with the voltage of the winding 28 obtained during the ON period of the main switch 4. At the start of turning on / off the main switch 4, the collector voltage of the phototransistor 39 is raised to limit the on-time width and current of the main switch 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device in which an output voltage is controlled to be constant by feedback control.

[0002]

2. Description of the Related Art When a switching power supply is used in a power supply circuit of a TV, a display, a computer system, or the like, it is necessary to provide a standby mode for saving power. In the standby mode, the load is light, so that the power supply due to the on / off of the switching element is intermittently interrupted, and the power supply can be maintained by the smoothing capacitor. When the interruption period is provided in this manner, the total number of ON / OFF operations of the switching elements is reduced, and the efficiency is improved.

[0003]

By the way, if the switching operation period and the switching non-operation period are alternately arranged in the standby mode, a current having a relatively large amplitude is supplied to the switching element in the first section (starting section) of the switching operation period. And flows through the primary winding of the output transformer,
Not only does the loss of the loss in the switching element is hindered, but also magnetostrictive noise (noise) is generated from the transformer. In order to solve this problem, it is conceivable to provide a soft start circuit for controlling the current of the switching element at the beginning of the switching operation period. However, it has been difficult to easily obtain a desired soft start effect regardless of a change in input voltage, a change in load, a change in the turns ratio of the output transformer, a change in inductance, and the like.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply capable of obtaining a good soft-start effect even when the input voltage or the like fluctuates.

The present invention for solving the above-mentioned problems and achieving the above-mentioned objects will be described with reference to the reference numerals in the drawings showing the embodiments. The present invention is connected between one end and the other end of a DC power supply (1). A series circuit of a primary winding (3) of a transformer (2) and a switch (4);
A secondary winding (6); an output rectifying / smoothing circuit (7, 8) connected to the secondary winding (6) for supplying a DC voltage to a load (11); , 8) a voltage detection circuit (19, 20) for detecting the output voltage;
A reference voltage source (22) for providing a control reference voltage;
Detection voltage obtained from the voltage detection circuit (19, 20)
And a reference voltage for constant voltage control of the reference voltage source (22).
Error signal forming circuit for forming an error signal composed of a difference signal
And (23), the front coupled to the error signal forming circuit <br/> Symbol semiconductor control element (39) so as to be able to flow substantially proportional to the current to the error signal, the switch (4) Current detection means (5) for detecting a flowing current; and adding a switch current (I1) detected by the current detection means (5) and a current (I2) of the semiconductor control element (39) to a previous value. The addition signal (V) for controlling the ON time width of the switch
f) turning on the addition means forming (4) and the switch (4)
.A switch that generates a switch control pulse for off control
A pulse generator (51) and a reference voltage source (5
4a, 54b) and an addition signal obtained from the addition means.
(Vf) and the reference voltage of the pulse width determining reference voltage source
(Vth), and the added signal (Vf) is
When it becomes higher than the reference voltage (Vth)
The control of the switch (4) by the switch control pulse
An on-time width control circuit (55,
56) , comprising: a feedback control power supply winding (28) electromagnetically coupled to the primary winding (3) of the transformer (2); and turning on the switch (4). The feedback control power supply capacitor (31) connected in parallel to the feedback control power supply winding (28) via the rectifying element (29) that conducts by the voltage obtained in the feedback control power supply winding (28) during the period. ), Wherein the feedback control power supply capacitor (31) is connected to the semiconductor control element (39) as the bias power supply. It is desirable that the feedback control system includes the light emitting diode 24 and the phototransistor 39 so that the primary side and the secondary side are insulated. Further, as described in claim 3, it is possible to configure so as to supply power to the first load 11 and the second load 12 which is lighter than the first load. It is desirable to provide a constant voltage circuit 57 that outputs the first and second voltages V11 and V12.

[0006]

According to the present invention, the bias voltage is applied to the feedback control semiconductor control element (for example, the phototransistor 39) by the winding 28 and the capacitor 31 for using the voltage during the ON period of the switch 4. Applied. Therefore, the semiconductor control element (for example, the phototransistor 39)
Bias voltage changes in proportion to the voltage of the power supply 1, so that the soft start effect of the capacitor 31 can be favorably obtained regardless of the change in the voltage of the power supply 1. Claim 2
According to the inventions of the fourth to fourth aspects, both the soft start and the voltage control can be easily achieved. Further, according to the invention of claim 3 , switching between the normal mode and the light load mode can be easily achieved.

[0007]

Embodiments and Examples Next, embodiments and examples of the present invention will be described with reference to FIGS. In FIG. 1 showing a switching power supply device according to an embodiment of the present invention, one end 1 of a DC power supply 1 comprising, for example, a rectifier circuit and a smoothing circuit.
A series circuit of a primary winding 3 having an inductance of the output transformer 2, a main switch 4 composed of an FET, and a current detecting resistor 5 as current detecting means is connected between the terminal a and the other end 1b. To configure a first output circuit, a first output smoothing capacitor 8 is connected in parallel to a secondary winding 6 of the transformer 2 via an output rectifier diode 7 as a first rectifier. . The polarity of the secondary winding 6 and the polarity of the rectifier diode 7 are determined so that the rectifier diode 7 conducts while the main switch 4 is off. First DC output terminals 9 and 10 connected to smoothing capacitor 8
Is connected to a load 11. To form a second output circuit, a second output smoothing capacitor 14 is connected to a tertiary winding 12 of the transformer 2 via an output rectifier diode 13 as a second rectifier. The polarity of the tertiary winding 12 is determined so that the rectifier diode 13 conducts during the off period of the main switch 4 as in the case of the secondary winding 6. A second load 17 is connected between the second output terminals 15 and 16 connected to the second smoothing capacitor 14. The ground terminal 10 of the first load 11 and the second terminal
The ground terminals 16 of the load 17 are connected to each other. In the normal mode, the first output voltage V01 between the first output terminals 9 and 10 is about 120 V, and the second output terminal 1
The second output voltage V02 between 5 and 16 is about 15V.

The switching power supply of FIG. 1 has a voltage control signal forming circuit 18 for controlling the first output voltage V01 between the first output terminals 9 and 10 to be constant. The voltage control signal forming circuit 18 includes voltage detecting resistors 19, 2 connected as voltage detecting circuits connected between the first output terminals 9, 10.
0, a resistor 21 and a Zener diode 22 for constituting a reference voltage source, and a transistor 23 as an error signal forming circuit, that is, an error amplifier. Transistor 2
The base of 3 is connected to the voltage dividing point of the voltage detection resistors 19 and 20, and the emitter is connected to a Zener diode 22 as a reference voltage source. The Zener diode 22 is connected between the DC output terminals 9 and 10 via the resistor 21. Therefore, the collector current of the transistor 23 changes according to the difference between the detection voltage and the reference voltage. A light emitting diode 24 is connected between the second output terminal 15 and the collector of the transistor 23 to convert the output of the voltage control signal forming circuit 18 into an optical signal.

To configure a control power supply,
A secondary winding 25 is provided. A third output smoothing capacitor 27 is connected in parallel to the fourth winding 25 via an output rectifier diode 26 as a third rectifier. The polarities of the quaternary winding 25 and the diode 26 are determined so that the diode 26 is turned on while the main switch 4 is off.

In order to execute the soft start control according to the present invention, a fifth winding 28 as a feedback control power supply winding, two rectifying diodes 29 and 30, and a fourth output smoothing capacitor 31 are provided. . The fifth winding 28 is formed continuously with the fourth winding 25, and both are divided by the intermediate tap P1. Fourth output smoothing capacitor 3
1 is connected in parallel to the fifth winding 28 via an output rectifier diode 29 as a fourth rectifier. The fifth output rectifier diode 30 is connected during the off period of the main switch 4.
It is connected between the cathode of the diode 26 and the cathode of the diode 29 with a polarity turned on by the voltage induced in the next winding 25. That is, the diode 30 is composed of the quaternary winding 25, the two diodes 26 and 30, and the capacitor 31.
Are connected so that the capacitor 31 can be charged in the closed circuit. Fifth winding 28 and diode 29
The polarity of is such that the diode 29 is turned on by the voltage induced in the fifth winding 28 while the main switch 4 is on, and the fourth output smoothing capacitor 31 which can be called a soft start capacitor can be charged. Has been determined.

A positive power supply line 33 of a switch control signal forming circuit 32 for controlling on / off of the main switch 4 is connected to one end of a capacitor 27 as a control power supply and is connected to a DC power supply 1 via a starting resistor 34. The ground line 35 is connected to the other end 1 of the DC power supply 1.
b and the other end of the capacitor 27. The control signal forming circuit 32 is connected to an input signal line 36 as a feedback control signal supply terminal. A feedback control signal Vf, which is a composite signal of a current detection signal and a constant voltage control signal, is input to the line 36. One end of the current detection resistor 5 is connected to the input signal line 36 via the resistor 37 to form this composite signal. A phototransistor 39 as a semiconductor control element is connected between a connection point 38 between the soft start capacitor 31 and the diodes 29 and 30 and the input signal line 36. Phototransistor 3
9 is optically coupled to the light emitting diode 24. The above-described connection of the current detection resistor 5 and the phototransistor 39 forms an addition circuit of the current I1 and the current I2. The switch control signal forming circuit 32 forms a switch control signal in response to the voltage Vf of the input signal line 36,
This is applied to the gate of main switch 4 by output line 40.

The power supply to the first load 11 is substantially stopped, and the second load 17 which is substantially lighter than the first load 11 is provided.
The first and second standby mode determining transistors 41 and 42, the Zener diode 43, the diode 44, and the two resistors 45 and 46 are provided for the operation of supplying power to the power supply, that is, the standby mode or the light load mode. I have.

The collector of the npn transistor 41 is connected to the cathode of the light emitting diode 24 via a Zener diode 43. The emitter of the transistor 41 is connected to the ground terminal 16, and the base is connected to a standby signal input terminal 47 as light load mode (standby mode) command means. A signal for turning on the transistor 41 in the standby mode and turning off the transistor 41 in the normal state is input to the standby signal input terminal 47.

The Zener diode 43 conducts when the transistor 41 is turned on in the standby mode, and has a Zener voltage of about 6V.

The emitter of the pnp transistor 42 is connected to the upper end of the secondary winding 6 via a diode 44, and the collector is connected to the second output terminal 15. The resistor 45 is connected between the emitter and the base of the transistor 42. The resistor 46 is a pnp transistor 42
And the collector of the npn-type transistor 41. Therefore, in standby mode, np
When the n-type transistor 41 is turned on, the pnp transistor 42 is also turned on, and both the secondary winding 6 and the tertiary winding 12 are connected to the second output smoothing capacitor 14 in parallel. However, since the voltage of the secondary winding 6 is higher than the voltage of the tertiary winding 12, the diode 13 is turned off during standby and the standby voltage is supplied from the secondary winding 6 to the second output terminals 15 and 16. Is done. During standby, the transistor 41 and the Zener diode 43 are turned on, so that the voltage V02 between the second output terminals 15 and 16 becomes 2
The standby voltage becomes much lower than the normal voltage of the next winding 6.

FIG. 2 shows details of the switch control signal forming circuit 32 and its related parts. The switch control signal forming circuit 32 includes a pulse generator 51 for generating a switch control pulse for turning on / off the main switch 4.
A drive circuit 52, a resistor 53, on-time width control reference voltage source resistors 54a and 54b, an on-time width control comparator 55, an on-time width control transistor 56, and a constant voltage circuit 57. Consists of The comparator 55 and the transistor 56 constitute an on-time width control circuit for the switch control pulse.

The pulse generator 51 includes a pulse forming comparator 58, a sawtooth wave generating capacitor 59, a discharging resistor 60, a charge controlling transistor 61, a Zener diode 62, resistors 63, 64, 65, 66 and diodes 67 and 68. One end of the saw-wave generating capacitor 59 is connected to the positive power supply line 33 via the charge control transistor 61, and the other end of the capacitor 59 is connected to the ground line 35. The discharging resistor 60 is connected in parallel to the capacitor 59. The Zener diode 62 functioning as a constant voltage source is connected between the base of the transistor 61 and the ground line 35. The base of the transistor 61 is connected via a resistor 63 to a constant voltage line 69 derived from the constant voltage circuit 57. One input terminal of the control pulse forming comparator 58 is connected to a constant voltage line 69 via a resistor 64,
The other input terminal is connected to one end of the saw-wave generating capacitor 59. The reference voltage resistor 65 and the diode 67 are connected between one input terminal and the output terminal of the comparator 58. The feedback resistor 66 and the diode 6
8 is connected between the base of the transistor 61 and the output terminal of the comparator 58.

The drive circuit 52 drives the main switch 4 in response to a switch control pulse, and has an input terminal a, an output terminal b, and a pair of power terminals c and d. The input terminal a is connected to the output line of the pulse generator 51, that is, the output line of the comparator 58, the output terminal b is connected to the gate (control terminal) of the main switch 4 via the resistor 53, and one power supply terminal c is connected to The power supply terminal d is connected to the positive power supply line 33, and the other power supply terminal d is connected to the ground line 35. As is apparent from FIG. 3, the drive circuit 52 includes first and second npn transistors 52a and 52b and a NOT circuit (inverting circuit) 52c. The collector of the first transistor 52a is connected to one power supply terminal c, the emitter is connected to the output terminal b, and the base is connected to the input terminal a. The collector of the second transistor 52b is connected to the output terminal b, the emitter is connected to the other power supply terminal d, and the base is connected to the input terminal a via the NOT circuit 52c. Therefore, the first and second transistors 5
2a and 52b operate in opposite directions.

One input terminal of the comparator 55 for determining the ON width of the main switch 4 is connected to the input signal line 36, and the other input terminal is connected to two reference voltage source resistors 54.
a, 54b. The reference voltage source resistors 54a and 54b are connected between the constant voltage line 69 and the ground line 35, and apply the divided voltage between them as the reference voltage for determining the ON width to the comparator 55. The power supply terminal of the comparator 55 is a constant voltage line 69 and a ground line 3
5 is connected. The transistor 56 as an on-time width control switch is connected between the output terminal of the pulse generation comparator 58 and the ground line 35, and its base is connected to the output terminal of the comparator 55. The output line of the phototransistor 39 and the output line of the resistor 37 are connected to each other to form an adding circuit. Therefore, the sum of the current feedback signal based on the current detection resistor 5 and the voltage feedback signal (voltage control signal) based on the phototransistor 39 is input to the input signal line 36. Therefore, the comparator 55 and the transistor 56 execute both the voltage feedback control and the current feedback control. During the ON period of the main switch 4, this current increases with time, and when this current detection voltage reaches the reference voltage Vth of the negative input terminal of the comparator 55, the comparator 5
5 becomes high level, the transistor 56 is turned on, the input terminal a of the drive circuit 52 is connected to the ground, and the main switch 4 is forcibly turned off.

The constant voltage circuit 57 is connected between the power supply line 33 and the ground line 35, and converts the voltage of the power supply line 33 to a constant voltage and outputs the voltage to a line 69. The voltage on line 69 is lower than the voltage on line 33. Although not shown, the power supply terminal of the comparator 58 is connected to the output line 69 of the constant voltage circuit 57. In addition, the constant voltage circuit 5
7 generates first and second level voltages depending on the magnitude of the voltage Vin on the line 33. The first level is a level at which the main switch 4 can form an on / off control signal, and the second level is a level at which the main switch 4 cannot form an on / off control signal.

[0021]

Next, when the switching power supply shown in FIGS. 1 and 2 is normal, the transistors 41 and 42 are off since the standby terminal 47 is at a low level, and a well-known constant voltage control circuit is formed. You. The operation at this time is shown in FIG.
The description will be made with reference to the period from t0 to t4. At time t0 in FIG. 5, the output voltage of the comparator 58 in FIG. 2 changes from the low level to the high level to generate a control pulse, and the corresponding gate control signal Vgs is applied to the main switch 4 as shown in FIG. As shown, the main switch 4 is turned on. As a result, a current I1 flows through a closed circuit including the DC power supply 1, the primary winding 3, the main switch 4, and the current detecting resistor 5. Since the primary winding 3 has an inductance, the current I1 increases with a gradient, the voltage of the current detecting resistor 5 changes in accordance with the waveform of the current I1, and the feedback control includes feedback information of the current I1. The input voltage Vf as a signal also increases with a slope as shown in FIG. When the voltage Vf corresponding to the current I1 reaches the reference voltage Vth at the time t1, the output of the comparator 55 changes from low level to high level, the transistor 56 is turned on, and the output terminal of the pulse generation comparator 58 is turned on. The transistor is connected to the ground via the transistor 56, and the ON period of the pulse ends. The output voltage of the pulse generating comparator 58 is t1
When the voltage becomes low at this point, the diode 67 is turned on, and the voltage V1 at the positive input terminal of the comparator 58 decreases from 6.5V to 3.5V as shown in FIG. It becomes lower than V2. Thereby, the comparator 58
Is maintained at a low level. Further, the comparator 58
Is low, the diode 68 is turned on, the base potential of the transistor 61 is lower than this emitter potential, the base-emitter of the transistor 61 is in a reverse bias state, and the transistor 61 is turned off. The charging of the capacitor 59 stops. As a result, the charge of the capacitor 59 is released through the resistor 60, and the voltage V2 decreases with a constant slope as shown by the broken line in FIG. At time t3, when the voltage of the capacitor 59, that is, the voltage V2 of the negative input terminal of the comparator 58 becomes lower than the voltage V1 of the positive input terminal, the output voltage of the comparator 58 returns to the high level again, and the next pulse is generated. FIG.
The voltage Vf based on the current I1 in the period t1 to t2 in (B) is generated by the current based on the storage action of the main switch 4. When the current I1 passing through the main switch 4 at time t2 becomes zero, the drain-source voltage Vds as the voltage between the pair of main terminals of the main switch 4 becomes higher than when it is on. During the period from t2 to t3, the current I1 becomes zero, so that the output of the comparator 55 for controlling the on-time width, that is, the current feedback control, is kept at a low level, and the transistor 56 for controlling the on-time width is also kept off. Therefore, the comparator 55 is not involved in the determination of the off period of the main switch 4, and the off period (for example, t1 to t3) is determined only depending on the discharge of the saw-tooth wave capacitor 59 and becomes constant. When the output voltage of the comparator 58 returns to the high level at time t3, the diode 67
And 68 are off. Thereby, the transistor 61
Is turned on again, the capacitor 59 is rapidly charged,
This voltage V2 becomes 5V. Also, the voltage V1 at the positive input terminal of the comparator 58 immediately becomes 6.5 V at the time t3. Therefore, the output voltage of the comparator 58 is kept at a high level.
The high level of the output voltage is set higher than 6.5V.

[0022]

[Voltage Control During Normal Load] When the voltage between both ends of the load 11 becomes higher than the reference value, for example, the input voltage Vf at the positive input terminal of the comparator 55 becomes higher. When the voltage reaches Vth, the output of the comparator 55 changes to a high level, and the transistor 56 is turned on, whereby the on-period of the PWM pulse ends, and the on-width of the PWM pulse is reduced. Since the OFF width of the PWM pulse train is constant, the duty ratio of the main switch 4 is reduced, and the output voltage is returned to the reference. When the output voltage becomes lower than the reference value, the operation is the reverse of that when the output voltage becomes higher.

[0023]

[Standby Operation] Next, the operation during standby will be described with reference to FIGS. As shown in FIG. 6A, the standby signal input terminal 47 goes high during standby. As a result, at the time of standby, the transistor 4
1 and 42 are kept on, and the voltage control signal forming circuit 18 is turned on.
Is interrupted, and an intermittent oscillation state occurs as shown in FIG. 6 (G). This intermittent oscillation is shown in FIG.
This occurs based on the change in the voltage Vin of the control power supply capacitor 27 shown in FIG. That is, in the standby mode, the transistor 41 and the Zener diode 43 become conductive, the current If of the light emitting diode 24 becomes relatively large, and the first and second output voltages V01 and V02 are reduced. As a result, the secondary winding 6, the tertiary winding 12, and the quaternary winding 25 of the transformer 2 are turned off while the main switch 4 is off.
Are lower than those in normal operation. Accordingly, the voltage Vin of the control power supply capacitor 27 connected to the quaternary winding 25 gradually decreases as shown in the section from t0 to t2 in FIG. It should be noted that even if an operation such as lowering the output voltages V01 and V02 occurs during standby, the voltage of the secondary winding 6 remains at the second output terminal 1 via the transistor 42.
5B, the second output voltage V02 is
As shown in the figure, it gradually rises in the section from t0 to t2. However,
At the time of standby, the second
Is limited, the second output voltage V02 is significantly lower than the normal first output voltage V01, and is a value suitable for the second load 17. When the control power supply voltage Vin supplied from the capacitor 27 reaches the oscillation stop threshold value Vb, the constant voltage circuit 57 of FIG.
A second constant voltage V12 shown in FIG. Since the second constant voltage V12 is set to a level at which the pulse generator 51 and the comparator 55 cannot operate normally, the supply of the ON / OFF control signal to the main switch 4 is not changed to the time t in FIG.
Interrupt at two points. However, the control power supply capacitor 27
Is connected to the DC power supply 1 via the starting resistor 34, the charging of the capacitor 27 via the starting resistor 34 starts, and this voltage Vin gradually increases as shown in the section from t2 to t3 in FIG. To rise. When the control power supply voltage Vin reaches the oscillation start voltage Va at the time point t3 in FIG. 6, the output voltage V69 of the constant voltage circuit 57 becomes the second constant voltage V2 as shown in FIG.
It becomes the first constant voltage V11 higher than 12. First constant voltage V
11 is set to a level at which the pulse generator 51 and the comparator 55 operate normally, so that the main switch 4 is turned on in the period t3 to t4 in FIG. 6 as in the period t0 to t2.
An off control signal is provided. As a result, the same operation as in the section between t0 and t2 occurs in the section between t3 and t4. In the standby mode, the main switch 4 has a pause period of the ON / OFF operation as shown at t2 to t3 in FIG. 6, so that the number of times of switching of the main switch 4 per unit time becomes smaller than that in the normal state, and 4, the loss is reduced and the efficiency is improved. During the stop period from t2 to t3, power is supplied to the second load 17 by the capacitor 14, and the voltage V02 gradually decreases.

[0024]

[Soft Start Operation] In this embodiment, the fourth output smoothing capacitor 31 for soft start is charged by the voltage of the fifth winding 28 of the transformer 2, and this capacitor 31
Is the collector voltage of the phototransistor 39 as a semiconductor control element, that is, the bias voltage. The fourth output rectifier diode 29 for charging the soft-start capacitor 31 has a polarity that is turned on by a voltage induced in the fifth winding 28 during the ON period of the main switch 4. Therefore, the voltage V3 of the soft start capacitor 31 is equal to the first voltage.
And the power supply 1 without depending on the second output voltages V01 and V02.
Voltage. Therefore, t0 or t3 in FIG.
When the ON / OFF operation of the main switch 4 is started, the capacitor 31 is rapidly charged by the voltage of the fifth winding 28 during the ON period of the main switch 4 as shown in FIG. High value. Phototransistor 3
Since the relationship between the collector-emitter voltage VCE 9 and the current amplification factor hfe is proportional as shown in FIG. 4, the current I2 of the phototransistor 39 flowing through the capacitor 31 as a bias power source is the ON / OFF of the main switch 4. 6 (E) and FIG. 7 (E) based on the rapid rise of the voltage V3 of the capacitor 31 at the start of turning off. Assuming that the voltage V3 of the capacitor 31 is constant, the current I2 of the phototransistor 39 is proportional to the current If of the light emitting diode 24 shown in FIG.
In the interval t3 to t4, the value gradually increases from a relatively low value to a high value. Note that the current If of the light emitting diode 24 is proportional to the second output voltage V02 in FIG. When the current If of the light emitting diode 24 is relatively low, the ON time width of the main switch 4 becomes long, the peak of the current Id shown in FIG. 7B becomes high, and the transformer 2 generates a magnetostrictive sound. In contrast, in the present embodiment,
Since the soft start capacitor 31 is provided and this voltage V3 is the collector bias voltage of the phototransistor 39, the current I2 of the phototransistor 39 increases in the on / off operation start section t0 to t1 of the main switch 4, The effect of reducing the ON time width of the main switch 4 and the current Id of the main switch 4 is obtained, and the magnetostrictive sound of the transformer 2 is suppressed. Light-emitting diode 2 after soft start
4, the current I2 of the phototransistor 39 gradually increases, and the on-time width of the main switch 4 and the peak of the current Id gradually decrease as shown in FIG. 7B. Note that the effect of the soft start can be obtained even when the normal operation of the switching power supply device is started.

As is apparent from the above description, according to the present embodiment, since the fifth winding 28 and the soft start capacitor 31 are provided, the main switch 4 and the primary winding 3 are connected during the intermittent oscillation period of the standby mode. Excessive current is prevented from flowing, and generation of magnetostrictive noise (noise) of the transformer 2 is suppressed. Also, the soft start capacitor 31
Since the voltage V3 changes in proportion to the voltage of the power supply 1, the peak of the current Id of the main switch 4 can be automatically suppressed to a predetermined level or less regardless of the change in the voltage of the power supply 1. That is, for example, when the voltage of the power supply 1 increases, the voltage V3 of the soft start capacitor 31 also increases, the ON time width of the main switch 4 and the effect of suppressing the peak of the current Id also increase, and the voltage of the power supply 1 increases. The increase in the peak of the current Id can be automatically suppressed. In addition,
Turn ratio of transformer 2, winding inductance, load 17
In the case where the current value changes, the operation for automatically correcting the current Id of the main switch 4 occurs. In this embodiment, the voltage of the primary winding 6 is supplied to the second load 17 via the transistor 42 at the time of standby, and the value of the second voltage V02 is limited to a predetermined value or less by the Zener diode 43. Therefore, the power supply to the load 17 and the intermittent oscillation operation during standby can be achieved by a relatively simple circuit.

[0026]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The configuration of the switch control signal forming circuit for turning on / off the main switch 4 can be variously modified. For example, by controlling charge or discharge of the capacitor 49, P
The width control of the WM pulse or the intermittent generation of the PWM pulse can be performed. (2) The main switch 4 can be replaced with a semiconductor switch such as a bipolar transistor. (3) A circuit configuration in which the light coupling circuit between the light emitting diode 24 and the phototransistor 39 is electrically omitted without the optical coupling circuit can be provided. (4) The secondary winding 6 is not provided independently of the tertiary winding 12.
Can also be used as the tertiary winding 12. (5) First to fourth output rectifier diodes 7, 13, 2
6, 29 may be rectifiers based on transistors or FETs, or synchronous rectifiers or circuits comprising parallel circuits of diodes and transistors or FETs.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a switch control signal forming circuit of FIG. 1 and a portion in the vicinity thereof;

FIG. 3 is a circuit diagram illustrating a driving circuit of FIG. 2 in detail;

FIG. 4 is a diagram showing characteristics of the phototransistor of FIG. 2;

FIG. 5 is a waveform diagram showing a state of each unit in FIG. 2 in a normal state.

FIG. 6 is a waveform diagram showing a state of each unit in FIG. 2 during standby.

FIG. 7 is an enlarged waveform diagram showing an on / off operation section in FIG. 6;

[Explanation of symbols]

 3 Primary winding 4 Main switch 31 Standby capacitor 39 Phototransistor 47 Standby signal input terminal

Continuation of the front page (72) Inventor Kengo Koike 3-6-3 Kitano, Niiza-shi, Saitama Sanken Electric Co., Ltd. (56) References JP-A 8-111975 (JP, A) JP-A 8-111977 (JP, A) JP-A-11-122921 (JP, A) JP-A-51-80614 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/28 H02M 3 / 335

Claims (4)

(57) [Claims] 1. A series circuit of a primary winding (3) and a switch (4) of a transformer (2) connected between one end and the other end of a DC power supply (1); Secondary winding (6) electromagnetically coupled to (3)
An output rectifying / smoothing circuit (7, 8) connected to the secondary winding (6) to supply a DC voltage to a load (11); and an output voltage of the output rectifying / smoothing circuit (7, 8). Detect
A voltage detection circuit (19, 20); and a reference voltage source (2 ) for supplying a constant voltage control reference voltage.
2) and a detection voltage obtained from the voltage detection circuit (19, 20)
And a reference voltage for constant voltage control of the reference voltage source (22).
Error signal forming circuit for forming an error signal composed of a difference signal
And (23), and coupled to said error signal forming circuit so as to be able to flow substantially proportional to the current in the error signal semiconductor control element (39), for detecting a current flowing through the switch (4) A current detection means (5); and a switch current (I) detected by the current detection means (5).
1) and the semiconductor control element (39) of the current (I2) and the pressure of the addition to for controlling the ON time width of the switch
Adding means for forming a computation signal (Vf), switch to on-off control of said switch (4)
A pulse generator (51) for generating a pulse control pulse, reference voltage sources for pulse width determination (54a, 54b), an addition signal (Vf) obtained from the addition means , and the pulse signal.
Comparison with the reference voltage (Vth) of the reference voltage source for determining the width,
The addition signal (Vf) is a reference voltage for determining the pulse width.
(Vth) when the switch control pulse
Formed so as to interrupt the control of the switch (4) by
A switching power supply apparatus having an on-time duration control circuit and (55, 56) that is, the said primary winding (3) to the magnetically coupled feedback control power winding of the transformer (2) (28 ), And in parallel with the feedback control power supply winding (28) via a rectifying element (29) that conducts by the voltage obtained in the feedback control power supply winding (28) during the ON period of the switch (4). And a feedback control power supply capacitor (31) connected thereto, wherein the feedback control power supply capacitor (31) is connected to the semiconductor control element (39) as the bias power supply. . 2. The method according to claim 1, wherein said semiconductor control element is provided with said error.
The error signal forming circuit is used for optical coupling to a signal forming circuit.
The switching power supply according to claim 1 , wherein a light emitting diode (24) is connected to the path, and the semiconductor control element is a phototransistor (39) optically coupled to the light emitting diode (24). 3. A switching power supply for supplying power to a first load (11) and a second load (17) having lower power consumption than the first load (11), comprising: A series circuit of a primary winding (3) and a switch (4) of a transformer having an inductance connected between one end and the other end of the power supply (1); and an electromagnetic coupling to the primary winding (3) Secondary winding (6)
A tertiary winding (12) electromagnetically coupled to the primary winding (3) and having a number of turns determined to induce a voltage lower than that of the secondary winding (6); Wire (3), said secondary winding (6) and said 3
A fourth winding (25) electromagnetically coupled to the secondary winding (12), and a fifth winding (28) electromagnetically coupled to the primary winding (3)
Connected between the secondary winding (6) and a first output terminal (9) for the first load (11), and connected to the secondary output terminal during the off-time of the switch (4). A first rectifying element (7) having a polarity conducting by a voltage induced in the winding (6); and the secondary winding (6) via the first rectifying element (7).
Output smoothing capacitor (8) connected in parallel to
Connected between the tertiary winding (12) and a second output terminal (15) for the second load (17), and connected to the tertiary winding during the off-time of the switch (4). A second rectifying element (13) having a polarity conducting by a voltage induced in the winding (12); and the tertiary winding (1) via the second rectifying element (13).
A second output smoothing capacitor (14) connected in parallel to 2); and the first and second output smoothing capacitors (8, 14).
Means for connecting the ground-side output terminals of each other, a voltage detection circuit (19, 20) for detecting the output voltage of the first output smoothing capacitor (8), and a constant voltage control reference voltage. Reference voltage source (2
(2) an error signal forming circuit (2) for forming an error signal corresponding to a difference between a detection voltage obtained from the voltage detection circuit (19, 20) and a reference voltage for constant voltage control of the reference voltage source (22).
3) is connected between one output terminal of the second output smoothing capacitor (14) and the output terminal of the error signal forming circuit (23), and the light emission amount is connected to the second output smoothing capacitor. A light emitting diode (24) whose polarity is determined so as to change in proportion to an output voltage (V02) of the capacitor (14); an output terminal of the error signal forming circuit (23); A first light load mode determining transistor (41) connected between the other output terminal of the output smoothing capacitor (14) via a zener diode (43); A signal indicating a light load mode for supplying power to the second load (17) without supplying power to the second load (17) is supplied to the first light load mode determining transistor (41). Load mode determination transformer A light load mode instructing means (47) for turning on a star (41), and connected between the secondary winding (6) and one terminal of the second output smoothing capacitor (14). A second light load mode determining transistor (42) controlled based on a signal indicating the light load mode so as to be turned on in the light load mode; Next winding (2
5) connected in parallel to the quaternary winding (25) via a third rectifying element (26) having a polarity conducting with the voltage obtained in the power supply (1); Output smoothing capacitor (27) connected to the other end of the circuit
And the fifth winding (28) during an ON period of the switch (4).
Is connected in parallel to the fifth winding (28) via a fourth rectifying element (29) having a polarity that conducts with a voltage obtained at the power supply (1) and a ground-side terminal of the fifth winding (28). A fourth output smoothing capacitor (31) connected to one end; a current detection resistor (5) connected between the switch (4) and the other end of the power supply (1); and a feedback control signal supply. A terminal (36), a combining resistor (37) connected between the feedback control signal supply terminal (36) and the current detection resistor (37), and an optically coupled light emitting diode (24); 4th
A phototransistor (39) connected between the output smoothing capacitor (31) and the feedback control signal supply terminal (36); the power supply (1); and the third output smoothing capacitor (2).
And a switch control pulse for controlling on / off of the switch (4) based on the voltage of the third output smoothing capacitor (27). A pulse generator (51) to be generated; reference voltage sources for pulse width determination (54a, 54b); a voltage (Vf) of the feedback control signal supply terminal (36); and a reference voltage source for pulse width determination (54a, 54b) is compared with the pulse width determining reference voltage (Vth), and when the voltage (Vf) of the feedback control signal supply terminal (36) becomes higher than the pulse width determining reference voltage (Vth), the switch is turned on. A switching power supply device comprising an ON time width control circuit (55, 56) for interrupting the ON control of the switch (4) by a control pulse. 4. A constant voltage circuit (5) for generating first and second voltages (V11, V12) between the third output smoothing capacitor (27) and the pulse generator (51).
7) is provided, wherein the constant voltage circuit (57) outputs the first voltage (V11) when power is normally supplied to the first load (11), and outputs the first voltage (V11) in the light load mode. The second voltage (V12) has a level for keeping the pulse generator (51) in a non-oscillating state. Switching power supply.