JP2002153059A - Switching power device and transformer used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily perform overcurrent protection in a switching power device. SOLUTION: In a spool 12 for a transformer for forming a current resonance type switching power device, a first groove 21, a second groove 22, a third groove 23, and a fourth groove 24 are formed. In the first, second, and third grooves 21, 22, 23, a primary winding N1, a secondary winding N2, and a tertiary winding N3 are arranged. The tertiary winding N3 is arranged between the primary winding N1 and the secondary winding N2.

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 of the type that obtains a voltage of a control circuit from a tertiary winding.

[0002]

2. Description of the Related Art For example, in a resonance type switching power supply disclosed in Japanese Patent Application Laid-Open No. 7-236271, a power supply voltage of a control circuit may be obtained from a tertiary winding, that is, an auxiliary winding. In a conventional transformer, a tertiary winding for obtaining a control voltage is arranged on the primary winding.

[0003]

By the way, if the load current in the output stage of the secondary winding is directly detected and the primary side switch is controlled to be turned off in the event of overload or short circuit, the circuit The configuration is necessarily complicated. Therefore, paying attention to the fact that the voltage of the tertiary winding changes in conjunction with the voltage of the secondary winding, switch control is performed when the voltage of the tertiary winding decreases with the voltage decrease of the secondary winding due to a load short circuit or the like. It is conceivable to make the circuit inoperative. However, in a conventional transformer having a configuration in which a tertiary winding is superimposed on a primary winding, the followability of the voltage of the tertiary winding with respect to the voltage change of the secondary winding is poor, resulting in an overcurrent or overload. Insufficient protection can be achieved.

[0004] It is an object of the present invention to provide a switching power supply device capable of achieving good and easy overcurrent protection.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems and to achieve the above object, the present invention provides a transformer having a primary winding, a secondary winding, and a tertiary winding which are electromagnetically coupled to each other. When,
Main power supply means, switch means for controlling a current or voltage supplied from the main power supply means to the primary winding, a control circuit for turning on / off the switch means, and the secondary winding And a control power supply for supplying a power supply voltage of the control circuit by a voltage of the tertiary winding, the switching power supply comprising: the primary winding of the transformer; The secondary winding is spaced apart from the transformer in the direction in which the core of the transformer extends,
The tertiary winding is arranged between the primary winding and the secondary winding, and relates to a switching power supply device.

It is preferable that a transformer be provided with a winding frame having first to third grooves.
Further, it is desirable to provide a switch for connecting the power supply terminal of the control circuit to the main power supply means only at the time of startup. Further, it is desirable to provide a fourth groove in the winding frame as described in claim 4. It is preferable that an insulating case is provided, a protrusion is provided on the case, and the protrusion is inserted into the fourth groove of the winding frame. According to a sixth aspect of the present invention, a half-bridge type switching power supply having a series circuit of the first and second switches and a current resonance capacitor can be provided. It is desirable that the tertiary winding be coupled to the secondary winding so that the voltage of the tertiary winding is lower than the minimum drive voltage of the control circuit when the load is short-circuited.

[0007]

According to the invention of each claim, the coupling of the tertiary winding to the secondary winding for obtaining the power supply voltage of the control circuit is strengthened. As a result, when the voltage of the secondary winding is reduced due to a load short circuit or the like, the voltage of the tertiary winding is significantly reduced, and control of the switch means by the control circuit can be interrupted. As a result, it is possible to prevent the circuit element in the passage where the overcurrent flows from being broken. Further, according to the first to sixth aspects of the present invention, since the tertiary winding is disposed between the primary winding and the secondary winding, the transformer can be made thinner than in the case of lap winding. it can. According to the second aspect of the present invention, the winding frame, ie, the bobbin is provided with the first, second and third grooves.
Since the secondary, tertiary and tertiary windings are arranged, the withstand voltage between the windings can be increased. According to the third aspect of the present invention, since the starting circuit is selectively connected to the control circuit, it is possible to reduce the power loss of the starting circuit. Also, an automatic return operation becomes possible. According to the invention of claim 4, the creepage distance between the primary winding and the secondary winding is increased by the fourth groove, and the withstand voltage is improved. According to the invention of claim 5, the creepage distance between the primary winding and the secondary winding can be further increased by the combination of the insulating case and the winding frame. Further, according to the invention of claim 6, protection of the current resonance type switching power supply device can be easily achieved.

[0008]

Next, a switching power supply according to an embodiment of the present invention will be described with reference to FIGS.

[0009]

First Embodiment A switching power supply according to a first embodiment shown in FIG. 1 comprises first and second insulated gate FETs connected between one end 1a and the other end 1b of a DC power supply 1. Series switch Q1 and Q2 and the primary winding N1
An output transformer T1 having a secondary winding N2 and a tertiary winding N3, a resonance capacitor C1 connected in series to a primary winding N1 of the output transformer T1, and a second switch Q1.
2 and a voltage resonance capacitor C2 connected in parallel to
And first and second clamping diodes D1 and D2 connected in reverse direction to the first and second switches Q1 and Q2,
A control circuit 2 connected to control terminals of the first and second switches Q1 and Q2; and a secondary winding N2 of an output transformer T1.
And diodes D3 and D3 connected to the secondary winding N2.
4 and a rectifying / smoothing circuit 3 comprising a smoothing capacitor Co.
And first and second output terminals 4a and 4b for connecting a load (not shown), a voltage detection circuit 5 connected between the output terminals 4a and 4b, and a rectifying and smoothing circuit 6 for a control power supply. ,
Control power supply voltage adjusting circuit 7 and control power supply capacitor 8
, An activation circuit 9 and an activation control circuit 10.

The first and second diodes connected in parallel in the reverse direction to the first and second switches Q 1 and Q 2 are connected to the first and second switches Q 1 and Q 2, respectively.
And the built-in diodes of the FETs constituting the second switches Q1 and Q2. Further, a capacitor similar to the capacitor C2 for voltage resonance can be connected in parallel to the first switch Q1.

The secondary winding N2 of the transformer T1 is divided into first and second secondary windings N2a and N2b. To form a full-wave rectifier circuit, one end and the other end of the secondary winding N2 are connected to one end of a capacitor Co via diodes D3 and D4, and a center tap P1 is connected to the other end of the capacitor Co. The first and second output terminals 4a and 4b are connected to one end and the other end of the capacitor Co.

A transformer T1 is a leakage transformer, and includes a magnetic core 11 having a gap G as shown in FIG. 5 in addition to windings N1, N2 and N3, and a bobbin or winding frame 12 as shown in FIG.
And an insulating case 13. The core 11 includes a combination of first and second E-shaped cores 11a and 11b, and a gap G is provided between the center legs of the first and second E-shaped cores 11a and 11b.

The winding frame 12 is a molded body of an insulating synthetic resin, and as is apparent from FIG. 7, a cylindrical portion 15 having a through hole 14 for inserting the center leg of the core 11, and a cylindrical portion 15. It has first, second, third, fourth, and fifth flange portions 16, 17, 18, 19, 20 protruding outward from the outer peripheral surface of the portion 15. The first, second, and third flanges are located between the flanges 16 to 20.
And fourth grooves 21 to 24. The first groove 21 is located between the first and second flanges 16 and 17, where the primary winding N1 is arranged as is apparent from FIG. The second groove 22 is located between the fourth and fifth flanges 19 and 20, where the secondary winding N2 is disposed. The third groove 23 is located between the second and third flanges 17, 18, where the tertiary winding N3 is disposed. The fourth groove 24 is located between the third and fourth flange portions 18 and 19, where no winding is arranged, and the insulating case 13 made of synthetic resin is used.
Is inserted.

The case 13 made of a synthetic resin molded body is divided into first, second, third and fourth cases 13a, 13b, 13c and 13d as shown in FIG. It is arranged so as to cover the surface in the direction. Although omitted in FIGS. 5 and 6, the windings N1, N2, N3,
The core 11, the winding frame 12, and the case 13 are integrated with an insulating paint or the like.

A well-known control rectifying / smoothing circuit 6 composed of a diode and a capacitor is connected to the tertiary winding N3 to constitute a drive power supply for the control circuit 2 of FIG. The control voltage adjusting circuit 7 connected to the rectifying / smoothing circuit 6 stabilizes the output voltage of the rectifying / smoothing circuit 6 and sends it to the control power supply capacitor 8. The capacitor 8 is connected between the power supply terminal 31 and the ground terminal 32 of the control circuit 2. The ground terminal 32 is connected to the other end 1b of the power supply 1.

The starting circuit 9 includes a starting switch 33, resistors 34, 35, 36, and Zener diodes 37, 38.
And a diode 39. A start switch 33 composed of an FET is connected between one end 1a of the main power supply 1 and the power supply terminal 31 of the control circuit 2 via a resistor 34, a Zener diode 37, a resistor 35, and a diode 39. The bias resistor 36 is connected between one end 1 a of the power supply 1 and the control terminal of the switch 33. The Zener diode 38 is connected in parallel between the gate and the source of the switch 33 and to the resistor 35.

The start control circuit 10 includes a transistor 40
, Diode 41, resistor 42, and capacitor 43
And two resistors 44 and 45. The collector of the NPN transistor 40 is connected to the control terminal (gate) of the start switch 33, and the emitter is connected to the other end 1 of the power supply 1.
b. One end of the tertiary winding N3 is connected to one end of a capacitor 43 via a diode 41 and a resistor 42. The other end of the capacitor 43 is a transistor 40
Connected to the emitter. A series circuit of the two resistors 44 and 45 is connected to the capacitor 43 in parallel. The interconnection point between the resistors 44 and 45 is connected to the base of the transistor 40. Therefore, the capacitor 43 is charged with the voltage of the tertiary winding N3 with a predetermined time constant, and discharged with the predetermined time constant via the resistors 44 and 45. When the transistor 40 is turned on after the start, the start switch 33 is turned off. Secondary winding N due to load short circuit etc.
When the voltage of 2 decreases, the discharge of the capacitor 43 starts, and the voltage of the capacitor 43 gradually decreases. Resistance 45
Is lower than the threshold value of the transistor 40, the transistor 40 is turned off.
Turns on. The time point at which the start-up switch 33 is turned on is set after the time point when the voltage at the power supply terminal 31 of the control circuit becomes lower than the operable minimum voltage due to the decrease in the voltage of the tertiary winding N3. As a result, when the voltage of the secondary winding N2 decreases due to a load short circuit or the like, the first and second switches Q
1 and Q2 are both turned off, causing a period during which the resonance operation is interrupted. Thereafter, the control voltage is supplied again via the start switch 33, and the first and second switches Q1, Q1
2 On / off operation starts automatically. If the short circuit of the load has not been eliminated, the voltage drop of the secondary winding N2 and the tertiary winding N3 occurs again, and the first and second switches Q1,
The on / off operation of Q2 is interrupted. Therefore, when an overload occurs, the switches Q1 and Q2 intermittently turn on and off.

FIG. 2 schematically shows the control circuit 2 of FIG. The control circuit 2 includes a phototransistor 50 optically coupled to the light emitting diode 5a of the voltage detection circuit 5, a resistor 51, a VCO (voltage controlled oscillator) 52, and first and second control signal forming circuits 53 and 54. Consists of The voltage detection circuit 5 of FIG. 1 generates an optical output in comparison with the voltage between the output terminals 4a and 4b. The resistance of the phototransistor 50 connected between the power supply terminal 31 and the ground terminal 32 in FIG. 2 via the resistor 51 changes in inverse proportion to the light output of the light emitting diode 5a. As a result, the control voltage obtained from the interconnection between the phototransistor 50 and the resistor 51 increases in proportion to the output voltage. The repetition frequency of the output pulse of the VCO 52 driven by the voltage of the power supply terminal 31 increases in proportion to the output voltage. The first control signal forming circuit 53 is a VCO
A control signal having an in-phase relationship with the output pulse of 52 is formed and sent to the control terminal of the first switch Q1. The second control signal forming circuit 54 sends a second control signal having a phase opposite to that of the first control signal to the control terminal of the second switch Q2. Control circuit 2
Stops the oscillation operation when the voltage of the power supply terminal 31 falls below a predetermined level. A means for detecting the current flowing through the first and second switches Q1 and Q2 is provided. When a large current continues to flow for a long time, the first and second switches Q1 and Q2 are forcibly turned off. A current protection circuit can be additionally provided.

FIG. 1 shows a switching power supply device. When the first switch Q1 is on, a current flows through a circuit composed of the power supply 1, the first switch Q1, the primary winding N1 having inductance, and the capacitor C1. This current is a current based on the series resonance of the primary winding N1 and the capacitor C1, has a waveform approximate to a sine wave, enables zero current switching at turn-on, and reduces switching loss. When the first switch Q1 is turned off, the second switch Q2 is turned on instead, and a resonance current flows through a circuit including the capacitor C1, the primary winding N1, and the second switch Q2. By repeating the above operation, currents in the first and second directions alternately flow through the primary winding N1 of the output transformer T1, and corresponding output voltages are obtained through the secondary windings N2a and N2b. D3, D
4 and rectified and smoothed by the capacitor C4.

When the voltages at the output terminals 4a and 4b become higher than a predetermined value in the apparatus shown in FIG. 1, the VCO 5 shown in FIG.
2 increases, and the on / off repetition frequency of the first and second switches Q1, Q2 increases. Conversely, when the voltages at the output terminals 4a and 4b are lower than a predetermined value, the operation is the opposite of the above.

The amplitude of the voltage of the primary winding N1 of the output transformer T1 varies depending on the on / off frequency f of the first and second switches Q1, Q2. FIG. 3 shows the response of the resonance circuit of the inductance L1 of the primary winding N1 and the capacitor C1. When the switches Q1 and Q2 are turned on and off at a frequency higher than the inherent resonance frequency f1 determined by L1 and C1, the response is reduced. In this embodiment, the output voltage is controlled by controlling the frequency of the VCO 52 in the range of f2 to f3.

When the load connected to the output terminals 4a and 4b is in an overcurrent state due to a short circuit or the like, the output voltages V0 and 2
The voltage of the next winding N2 drops. FIG. 4 shows this state. When the load current I becomes larger than I1, the output voltage V0 and the voltage V3 of the tertiary winding N3 drop, and the output voltage V0 becomes almost zero volts at the current I2. In the present embodiment, the tertiary winding N3 is not superposed on the primary winding N1, but is arranged between the primary winding N1 and the secondary winding N2. Accordingly, the degree of coupling of the tertiary winding N3 to the secondary winding N2 becomes larger than before, and the voltage V3 of the tertiary winding N3 decreases following the decrease of the output voltage V0 well, and the short-circuit current I2 decreases. The minimum drive voltage V of the control circuit 2 before flowing.
min, and at substantially the same time, the voltage Vcon of the power supply terminal 31 of the control circuit 2 becomes lower than the minimum voltage Vmin. As a result, when the output voltage V0 starts dropping, the control circuit 2 interrupts the on / off control of the first and second switches Q1 and Q2, suppresses an increase in load current, and suppresses the diode D.
3, D4 and circuit elements such as load are protected. When the voltage V3 of the tertiary winding N3 decreases, the charging voltage of the capacitor 43 of the activation control circuit 10 also decreases. When the voltage falls below a predetermined value, the transistor 40 is turned off and the activation switch 33 is turned on. Become. However, the capacitance of the capacitor 43 and the values of the resistors 44 and 45 are determined so as to prevent the start-up switch 33 from being turned on simultaneously with the droop of the output voltage V0. Therefore, when the output voltage V0 drops, first, the voltage Vcon of the power supply terminal 31 of the control circuit 2
Becomes lower than the minimum voltage Vmin, and the on / off operations of the first and second switches Q1 and Q2 are interrupted. After a predetermined time from the start of the interruption, the start switch 33 is turned on and the control circuit starts operating. I do. First and second switches Q1
If the load is short-circuited or overloaded even after the on / off of Q2 is restarted, the output voltage V0 drops again and the same operation is repeated. When the load is momentarily short-circuited or overloaded, the operation returns to the normal operation after the ON / OFF of the first and second switches Q1 and Q2 is restarted.
In the conventional device, since the coupling between the secondary winding N2 and the tertiary winding N3 is weak, the voltage of the tertiary winding N3 is reduced when the output voltage V0 drops as shown by the broken line V3 'in FIG. V3 'does not drop to the minimum voltage Vmin and the control circuit 2
Continued operation and failed to achieve overcurrent protection.

This embodiment has the following effects. (1) Since the tertiary winding N3 is disposed between the primary winding N1 and the secondary winding N2, a conventional transformer in which the tertiary winding N3 is arranged so as to overlap the primary winding N1 is used. Compared to the case, the coupling of the tertiary winding N3 to the secondary winding N2 is stronger, and conversely, the coupling of the tertiary winding N3 to the primary winding N1 is weaker. As a result, the voltage V3 of the tertiary winding N3 changes satisfactorily following the voltage of the secondary winding N2, and the ON / OFF of the first and second switches Q1 and Q2 is interrupted when the output voltage V0 drops. Thus, the circuit element can be protected. (2) The on / off operation of the first and second switches Q1 and Q2 can be automatically returned by the operation of the start control circuit 10. (3) Since the tertiary winding N3 is not superimposed on the primary winding N1,
The thickness of the transformer T1 can be reduced. (4) The first, second and third grooves 21 and 2 of the bobbin 20
Since the primary, secondary, and tertiary windings N1, N2, and N3 are disposed on the second and the second 23, the withstand voltage between them can be improved. (5) The case 13 is provided, and the protrusion 25 is further
The fourth groove 24 allows the withstand voltage to be improved to a high level.

[0024]

Second Embodiment Next, a second embodiment will be described with reference to FIG. However, in FIG. 8, substantially the same parts as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted. The switching power supply of the second embodiment has the same configuration as that of the first embodiment except that the transformer T1 of the first embodiment shown in FIGS. 1 to 7 is modified. FIG. 8 shows the second
1 shows the transformer of the first embodiment without a core.
In the transformer of FIG. 8, the primary winding N1 and the tertiary winding N
4 and a fourth groove 24 is arranged between the third groove 24 and the case 13.
Is inserted. Therefore, the degree of coupling of the tertiary winding N3 of FIG. 8 to the secondary winding N2 is greater than that of FIG. According to the second embodiment, the same effect as that of the first embodiment can be obtained.

[0025]

Third Embodiment Next, a resonance type switching power supply according to a third embodiment will be described with reference to FIG. However, in FIG. 9, portions common to FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In the circuit of FIG. 9, first and second resonance capacitors C1a and C1b are provided instead of one resonance capacitor C1 of FIG. 1, and a series circuit of the first and second resonance capacitors C1a and C1b is connected to a power supply. One end 1a and the other end 1b of 1
And a primary winding N1 having an inductance.
Is connected between the interconnection point of the first and second switches Q1 and Q2 and the interconnection point of the first and second resonance capacitors C1a and C1b, and the other components are the same as those shown in FIG. It is. The voltage resonance capacitors C2a and C2b are connected in parallel to the switches Q1 and Q2.

In the switching power supply of FIG.
Series resonance occurs due to the capacitance of the parallel circuit of the first and second resonance capacitors C1a and C1b and the inductance of the primary winding N1. In FIG. 9, the resonance capacitor C1
Since it is substantially the same as FIG. 1 except for the connection of a and C1b,
According to the third embodiment, the same effect as that of the first embodiment can be obtained.

[0027]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) An additional inductance for forming a current resonance circuit can be connected in series with the primary winding N1. (2) The rectifying and smoothing circuit 3 can be modified to a bridge type full-wave rectifying circuit. (3) The internal configuration of the control circuit 2 can be variously modified. (4) Overcurrent protection can be performed in multiple stages. For example, primary winding N1 or switch Q1,
Current detecting means for detecting a current flowing through Q2 is provided, and when the detected current value obtained from the current detecting means is equal to or higher than a predetermined level, switches Q1 and Q2 can be forcibly turned off. (5) The transformer can have a two-leg configuration. (6) The present invention can be applied not only to the resonance type switching power supply device of FIGS. 1 and 9 but also to a flyback type switching power supply device of a type that obtains the power supply voltage of the control circuit from the tertiary winding N3. . (7) The switches Q1 and Q2 can be semiconductor switches such as bipolar transistors.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a switching power supply device according to a first embodiment.

FIG. 2 is a block diagram schematically showing a control circuit of FIG. 1;

FIG. 3 is a diagram showing a relationship between on / off frequencies of switches Q1 and Q2 in FIG. 1 and a response of a resonance circuit of L1 C1.

FIG. 4 is a diagram showing a relationship between a load current, an output voltage, and a voltage of a tertiary winding of the circuit of FIG. 1;

FIG. 5 is a central longitudinal sectional view of the transformer of FIG. 1;

FIG. 6 is a sectional view taken along line AA of FIG. 5;

FIG. 7 is a sectional view showing the bobbin of FIG. 5;

FIG. 8 is a cross-sectional view illustrating a part of the transformer according to the second embodiment.

FIG. 9 is a circuit diagram illustrating a switching power supply device according to a third embodiment.

[Explanation of symbols]

Q1, Q2 switches N1, N2, N3 primary, secondary and tertiary windings 2 control circuit 9 starting circuit 10 starting control circuit 12 winding frame 21, 22, 23, 24 first, second, third and fourth Grooves,

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H730 AA02 AA14 AS01 BB26 BB57 BB76 DD04 DD27 EE03 EE08 FD01 FF19 FG07 VV03 VV06 XX15 XX16 XX28 XX33

Claims (7)

[Claims] 1. A transformer having a primary winding, a secondary winding, and a tertiary winding electromagnetically coupled to each other, a main power supply, and a current supplied from the main power supply to the primary winding. Switch means for controlling a voltage, a control circuit for controlling on / off of the switch means, an output circuit connected to the secondary winding, and the control circuit based on a voltage of the tertiary winding. A switching power supply device comprising a control power supply for supplying a power supply voltage of the transformer, wherein the primary winding and the secondary winding of the transformer are arranged apart from each other in a direction in which a core of the transformer extends, A switching power supply device, wherein a tertiary winding is disposed between the primary winding and the secondary winding. 2. The transformer has a winding frame for winding the primary winding, the secondary winding, and the tertiary winding, and the winding frame arranges the primary winding. And a second groove for arranging the secondary winding, and a third groove for arranging the tertiary winding, wherein the third groove is provided with the first groove. 2. The switching power supply device according to claim 1, wherein the switching power supply device is formed between the first groove and the second groove. 3. A starting switch connected between the main power supply means and a power supply terminal of the control circuit; a voltage detection means for detecting a voltage of the tertiary winding; and the voltage detection means. 3. The switching power supply device according to claim 1, further comprising means for controlling the start-up switch to be turned off when a voltage equal to or higher than a predetermined value is detected. 4. The winding frame has a fourth groove between the second groove and the third groove or between the first groove and the third groove.
3. The switching power supply device according to claim 2, wherein the switching power supply device has: 5. An insulating case for covering the primary winding, the secondary winding, and the tertiary winding, wherein the case has a projection, and the projection is The switching power supply device according to claim 4, wherein the switching power supply device is inserted in the groove (4). 6. The switch means comprises a series circuit of first and second switches connected between one end and the other end of the main power supply means, and the primary winding includes a current resonance capacitor. The switching power supply device according to any one of claims 1 to 5, wherein the switching power supply device is connected in parallel with the second switch via a second switch. 7. A transformer having a primary winding, a secondary winding, and a tertiary winding electromagnetically coupled to each other, a main power supply, and a current supplied from the main power supply to the primary winding. Switch means for controlling a voltage, a control circuit for controlling on / off of the switch means, an output circuit connected to the secondary winding, and the control circuit based on a voltage of the tertiary winding. A switching power supply device comprising: a control power supply for supplying a power supply voltage of the third winding, wherein the voltage of the tertiary winding maintains the operation of the control circuit before an output voltage becomes zero due to a short circuit of a load. A switching power supply, wherein the tertiary winding is coupled to the secondary winding so as to be lower than a minimum drive voltage that can be achieved.