JP3281393B2 - Switching power supply - Google Patents

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 which employs a resonance frequency control method suitable for a power supply for a television receiver, for example.

[0002]

2. Description of the Related Art Conventionally, AV devices such as television receivers have been used.
2. Description of the Related Art In audio-visual devices, a switching power supply device having relatively high efficiency is employed as a means for achieving a small and lightweight device.

FIG. 2 shows a configuration of a switching power supply of a resonance frequency control type as an example of a conventional switching power supply. In FIG. 2, A of 100 V at 50-60 Hz
The AC voltage output from the C power supply 1 is converted into a DC voltage Vdc by a rectifier circuit 2, and the DC voltage Vdc is converted into an AC voltage Vac by a switching circuit 4 having a quadrature type saturable reactor transformer 6 and switching transistors 7 and 8. Is converted. The switching circuit 4 is a self-excited oscillation circuit. The saturable reactor transformer 6
Has drive coils 9 and 10, a control coil 11, and a core. The self-excited oscillation circuit intermittently oscillates by positively feeding back part of the output of the amplifying means to the input side, as is well known. In the present specification, the operation of the self-excited oscillation circuit itself is not related to the gist of the present invention. Therefore, in FIG. 2, a positive feedback path is not shown in order to avoid complicating the drawing. ing.

The output AC voltage Vac of the switching circuit 4
Is supplied to a primary coil 17 constituting a saturable reactor transformer 16 through a series resonance capacitor 15. The saturable reactor transformer 16 has a secondary coil 18, a control coil 19, and a core in addition to the primary coil 17.

[0005] The output of the secondary coil 18 is supplied to a rectifier circuit 22 composed of a diode bridge circuit 20 and a smoothing capacitor 21. + B which is the output of the rectifier circuit 22
The voltage (hereinafter, referred to as rectified output B or voltage B as necessary) is supplied to a load circuit 24 as a main load circuit of a main power supply unit 25 through an output terminal 23.

The voltage B is supplied to a control circuit 27 having a shunt regulator (not shown) and the like. The output of the control circuit 27 is supplied to the control coil 19 of the saturable reactor transformer 16.

On the other hand, the output AC voltage Vac of the switching circuit 4 is supplied to the primary coil 33 of the resonance transformer 32 through the resonance capacitor 31, and the resonance transformer 3
The secondary output appearing in the second secondary coil 34 is supplied to a rectifier circuit 37 having a diode bridge 35 and a smoothing capacitor 36.

The rectified output voltage Vs of the rectifier circuit 37 is supplied through an output terminal 39 to a load circuit 40 as an auxiliary load circuit of a standby power supply 41. Note that the standby power supply is a power supply that continues to supply power to some of the circuits even after a power switch (for example, arranged in series with the capacitor 15) of the main power supply unit 25 is turned off. It is. For example, a power supply is supplied to a remote control receiving unit that also operates on / off of a main power switch of the television receiver main body, and a BS tuner and a BS converter that perform reservation reception by a timer and the like.

The voltage Vs is controlled by the operation of the control circuit 42.
The voltage is stabilized. The control circuit 42 includes the transistor 4
3 and 44 and a constant voltage diode 45. A bias current is supplied from the voltage Vs to the constant voltage diode 45 through the resistor 46, and the terminal voltage of the constant voltage diode 45 is divided by the resistor 47 and the resistor 48 to generate the reference voltage Vref. This reference voltage Vref is supplied to the emitter terminal of the transistor 44. The voltage Vs is divided and supplied to the base terminal of the transistor 44 through the resistor 51 and the resistor 52. The collector terminal of the transistor 44 is connected to a voltage V
s, and the emitter terminal is connected to the base terminal of the transistor 43 connected to the voltage Vs.
The collector terminal of transistor 43 is connected to control coil 11 constituting saturable reactor transformer 5.

Next, the stabilizing operation of the voltage B and the voltage Vs of the switching power supply according to the prior art configured as described above will be described.

The voltage B is compared with a reference voltage in a control circuit 27, and a current corresponding to the comparison result is supplied to the control coil 19, so that the saturable reactor transformer 16 is controlled.
The impedance value of the saturable reactor transformer 16 viewed from the primary side changes from the primary side to the secondary side, and the series resonance frequency of the series resonance circuit including the inductance and the capacitor 15 changes. By such feedback control, the voltage B is maintained at a constant value corresponding to the reference voltage.

On the other hand, the voltage Vs is compared with the reference voltage Vref, and a control current Ic according to the comparison result is supplied to the control coil 11 of the saturable reactor transformer 6 so that the inductance values of the drive coils 9 and 10 are changed. Changes, and the switching frequency of the switching circuit 4 changes. In this case, since the series resonance frequency of the capacitor 31 and the resonance transformer 32 is set to a value lower than the switching frequency, the rectified output Vs is controlled to change in inverse proportion to the increase or decrease of the switching frequency.
This is because the operation is performed in a region where the series impedance of the capacitor 31 and the inductance viewed from the primary side of the resonance transformer 32 increases in proportion to the frequency. The voltage Vs controlled in this way is kept at a constant value corresponding to the reference voltage Vref.

[0013]

By the way, in the switching power supply employing the conventional resonance frequency control method shown in FIG. 2, the load state of the standby power supply 41 is the state of the equipment, for example, the BS (for satellite broadcasting) tuner. Considering the case where the voltage changes according to the presence or absence of a circuit, when the load circuit 40 as the auxiliary load circuit has a relatively light load, the voltage Vs tends to increase as described above. Switching frequency increases. Further, when the load circuit 40 has a relatively heavy load, the switching frequency becomes lower because the voltage Vs tends to decrease.

However, in particular, the switching circuit 4
When the frequency becomes high, the current flowing through the switching transistors 7 and 8 increases, and there is a problem that the heat generation of the transistors 7 and 8 increases. Further, the current flowing through the winding of the saturable reactor transformer 6 as an oscillation transformer increases, and the saturable reactor transformer 6
This causes a problem that the heat generation of the device increases. In addition, the leakage magnetic flux generated from the saturable reactor transformer 6 becomes large, so that noise as unnecessary radiation becomes large and the efficiency becomes low.

Therefore, in order to prevent these problems,
Conventionally, adoption of a transistor having a relatively large rated current capacity, enlargement of its heat dissipating fin, thickening of the winding of the saturable reactor transformer 6, and providing a magnetic shield case with a high shielding effect to the saturable reactor transformer 6 We were taking measures such as attaching.

However, when such measures are taken, the configuration of the switching circuit 4 becomes large, and as a result, the size and weight of the device cannot be sufficiently reduced, and the cost of the device increases. Was.

The present invention has been made in view of the above problems, and has as its object to provide a switching power supply device in which a change in the frequency of a switching circuit is relatively small with respect to a change in the load state of an auxiliary load circuit. I do.

[0018]

SUMMARY OF THE INVENTION A switching power supply according to the present invention comprises a saturable reactor transformer having at least a first control coil and a drive coil whose inductance value changes in accordance with a current flowing through the first control coil. When,
A switching element for switching by a signal from a drive coil of the saturable reactor transformer, a switching circuit for interrupting the supplied DC, and a first resonance circuit for supplying an output of the switching circuit to a primary side. A first resonance transformer having a second control coil and a first resonance circuit having a resonance frequency lower than a switching frequency of a switching circuit together with the first resonance transformer; And the capacitor
A first rectifier circuit for rectifying a secondary output of the first resonance transformer, a main load circuit to which the rectified output of the first rectifier circuit is supplied, and an output voltage of the first rectifier circuit are detected. When the output voltage of the first rectifier circuit is increased by changing the current supplied to the second control coil of the first resonance transformer according to the comparison result, A first control circuit that changes the resonance frequency of the first resonance circuit so that the resonance frequency of the first resonance circuit becomes higher, and a second resonance transformer in which the output of the switching circuit is supplied to the primary side. A second capacitor forming a resonance circuit having a resonance frequency lower than the switching frequency of the switching circuit together with the second resonance transformer;
Rectifier circuit for rectifying the secondary output of the resonance transformer, and an auxiliary load circuit to which the rectified output of the second rectifier circuit is supplied, the auxiliary load circuit having a lighter load than the main load circuit. And the output voltage of the second rectifier circuit is detected and compared with the reference voltage, and the current supplied to the first control coil of the saturable reactor transformer of the switching circuit is changed in accordance with the comparison result to obtain the second voltage. A second control circuit that changes the switching frequency of the switching circuit so that the switching frequency of the switching circuit increases when the output voltage of the rectifier circuit increases, and the output of the second control circuit is detected. When the output of the second control circuit is to increase the switching frequency of the switching circuit, the reference voltage is changed in a direction to suppress the increase in the switching frequency. Those having a voltage variable circuit.

[0019]

According to the present invention described above, the switching circuit for interrupting the supplied direct current includes at least a first control coil and a drive coil whose inductance value changes according to the current flowing through the first control coil. A saturable reactor transformer, and a switching element that is switched by a signal from a drive coil of the saturable reactor transformer. A primary side of a first resonance transformer having a second control coil is provided with a switching circuit. Output is supplied,
The first resonance transformer and the first capacitor form a first resonance circuit having a resonance frequency lower than the switching frequency of the switching circuit. Rectifying the secondary output, supplying the rectified output of the first rectifier circuit to the main load circuit, the first control circuit detecting the output voltage of the first rectifier circuit and comparing the output voltage with the reference voltage; The first according to the comparison result
The current supplied to the second control coil of the resonance transformer is changed so that when the output voltage of the first rectifier circuit increases, the first resonance circuit increases the resonance frequency. The resonance frequency of the resonance circuit is changed, and the output of the switching circuit is supplied to the primary side of the second resonance transformer, and the second resonance transformer and the second capacitor determine the output of the switching circuit from the switching frequency of the switching circuit. And a secondary output of the second resonance transformer is rectified by the second rectifier circuit, and the rectified output of the second rectifier circuit is more loaded than the main load circuit. Is supplied to a light auxiliary load circuit, the second control circuit detects the output voltage of the second rectifier circuit, compares the output voltage with the reference voltage, and according to the comparison result, determines the output voltage of the saturable reactor transformer of the switching circuit. The switching frequency of the switching circuit is changed so that the switching frequency of the switching circuit is increased when the output voltage of the second rectifier circuit is increased by changing the current supplied to the control coil. Detecting the output of the second control circuit,
When the output of the second control circuit is to increase the switching frequency of the switching circuit, the reference voltage is changed in a direction to suppress the increase in the switching frequency.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the switching power supply according to the present invention will be described below with reference to the drawings. In the drawings referred to below, components corresponding to those shown in FIG. 2 described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows the configuration of an embodiment of the switching power supply of the present invention. In FIG. 1, 50 to 60
An AC voltage output from an AC power supply 1 of 100 V at 100 Hz is converted into a DC voltage Vdc by a rectifier circuit 2, and the DC voltage Vdc is converted by a switching circuit 4 having an orthogonal saturable reactor transformer 6 and switching transistors 7 and 8. It is converted to AC voltage Vac. In addition,
The switching circuit 4 is a self-excited oscillation circuit. Further, the saturable reactor transformer 6 has drive coils 9 and 10, a control coil 11, and a core. The self-excited oscillation circuit intermittently oscillates by positively feeding back part of the output of the amplifying means to the input side, as is well known. In the present specification, the operation of the self-excited oscillation circuit itself is not related to the gist of the present invention. Therefore, in FIG. 1, a positive feedback path is not shown in order to avoid complicating the drawings. ing.

The output AC voltage Vac of the switching circuit 4
1 constitutes a saturable reactor transformer 16 as a first resonance transformer through a series resonance capacitor 15.
It is supplied to the next coil 17. The saturable reactor transformer 16 has a secondary coil 18, a control coil 19, and a core in addition to the primary coil 17.

The output of the secondary coil 18 is a first output comprising a diode bridge circuit 20 and a smoothing capacitor 21.
Is supplied to the rectifier circuit 22 as the rectifier circuit of FIG. + B voltage output from the rectifier circuit 22 (hereinafter referred to as voltage B)
Is supplied to a load circuit 24 as a main load circuit of a main power supply unit 25 through an output terminal 23.

The voltage B is supplied to a control circuit 27 having a shunt regulator 61 through a voltage dividing resistor.
The collector output of the output transistor 62 of the control circuit 27 is supplied to the control coil 19 of the saturable reactor transformer 16. The control circuit 27 operates as follows.

The input DC voltage Vdc changes, or the load of the load circuit 24 fluctuates in accordance with the operation state of the device, for example, the input DC voltage Vdc tends to increase, or the load decreases. When the voltage B is going to increase, the gate voltage of the shunt regulator 61 increases and the cathode voltage decreases. Therefore, the base voltage of the transistor 62 decreases, and the control coil 19
The current flowing through becomes smaller. As a result, the inductance value of the primary coil 17 increases, and the primary coil 17
And the current flowing through the secondary coil 18 decreases. Therefore, an increase in the rectified output voltage B is suppressed.

By such a feedback operation, the output voltage B is maintained at a constant voltage value corresponding to the reference voltage constituting the shunt regulator 61. The DC power supply 63 constituting the control circuit 27 is a power supply formed using a power transformer (not shown), a rectifier circuit, a three-terminal regulator, and the like, which are directly connected to the AC power supply 1.

On the other hand, the output AC voltage Vac of the switching circuit 4 is supplied through the resonance capacitor 31 to the primary coil 33 of the resonance transformer 32 as a second resonance transformer.
Supplied to A secondary output appearing in the secondary coil 34 of the resonance transformer 32 is supplied to a rectifier circuit 37 as a second rectifier circuit having a diode bridge 35 and a smoothing capacitor 36.

The rectified output voltage Vs of the rectifier circuit 37 is supplied through an output terminal 39 to a load circuit 40 as an auxiliary load circuit of the standby power supply 41.

The voltage Vs is controlled by the operation of the control circuit 42.
The voltage is stabilized. The control circuit 42 includes the transistor 4
3 and 44 and a constant voltage diode 45. A bias current is supplied from the voltage Vs to the constant voltage diode 45 through the resistor 46, and the voltage of the constant voltage diode 45 is divided by the resistor 47 and the resistor 48 to generate the reference voltage Vref. This reference voltage Vref is supplied to the emitter terminal of the transistor 44. The voltage Vs is divided and supplied to the base terminal of the transistor 44 through the resistor 51 and the resistor 52. The collector terminal of the transistor 44 is connected to the voltage Vs through the resistor 53, and the emitter terminal is connected to the base terminal of the transistor 43 whose emitter terminal is connected to the voltage Vs. The collector output current of the transistor 43 is used as the control current Ic for the control coil 11 constituting the saturable reactor transformer 5.
Supplied to

In this case, since one end of the control coil 11 is grounded, a terminal voltage Vc is generated at the other end to which the control current Ic is supplied. Terminal voltage Vc of control coil 11
A resistor 65 and a resistor 66 are connected between the point at which occurs and the connection point between the resistor 47 and the resistor 48. Resistor 6
A capacitor 67 for preventing oscillation is connected from the connection point of the resistor 5 and the resistor 66 to the ground. Here, the resistor 65 and the resistor 66 constitute a voltage variable circuit 68 that changes the reference voltage Vref according to the terminal voltage Vc of the control coil 11.

Next, the operation of stabilizing the voltage Vs will be described.

The load circuit 40 of the standby power supply unit 41
For example, when it becomes lighter (when the load current Is becomes smaller),
The voltage Vs increases. Therefore, the base terminal voltage of transistor 44 increases, and the collector current of transistor 43 increases. The control current Ic increases due to the increase in the collector current. Due to the increase of the control current Ic, the inductance values of the drive coils 9 and 10 constituting the saturable reactor transformer 6 decrease, and the switching frequency of the switching circuit 4 increases.

In this case, since the series resonance frequency of the capacitor 31 and the resonance transformer 32 is set to a value lower than the switching frequency, control is performed so that the rectified output Vs changes in inverse proportion to the increase or decrease of the switching frequency. You. This is because the operation is performed in a region where the series impedance of the capacitor 31 and the inductance viewed from the primary side of the resonance transformer 32 increases in proportion to the frequency.

Therefore, when the switching frequency of the switching circuit 4 increases, the current flowing through the primary coil 33 of the resonance transformer 32 decreases, so that the power supplied to the secondary coil 34 decreases, and the rectified voltage Vs decreases. It is controlled in the downward direction.

Here, when the collector current of the transistor 43 increases, a part of the increased collector current flows to the resistors 65 and 66, so that the reference voltage Vref
Will rise. This can be considered that the reference voltage Vref changes according to the increase in the terminal voltage Vc.

When the reference voltage Vref increases, the voltage Vs increases in relation to the ratio between the resistors 51 and 52. When the voltage Vs increases, the base current of the transistor 44 decreases, so that the collector current of the transistor 43 decreases. As a result, an increase in the control current Ic supplied to the control coil 11 is suppressed, and the switching circuit 4
Is suppressed from increasing in the switching frequency.

Explaining concrete numerical values for the effect of suppressing the increase of the switching frequency, when the circuit operates at a voltage Vs = 7 V and a switching frequency of about 140 kHz and the load circuit 40 becomes lightly loaded, the conventional circuit shown in FIG. In the technology, the voltage Vs = 7V is constant, but the switching frequency increases to about 200 kHz. On the other hand, according to the example in FIG. 1, the voltage Vs changes to Vs ≒ 7.5 V, but the switching frequency is suppressed to about 180 kHz.

As described above, according to the above-described embodiment, the voltage variable circuit 68 controls the control circuit of the auxiliary load circuit 40 according to the terminal voltage Vc of the control coil 11 of the saturable reactor transformer 6 constituting the switching circuit 4. 42 reference voltage Vr
ef is changed so that the auxiliary load circuit 4
When the load state of 0 changes, the rectified voltage Vs for supplying current to the auxiliary load circuit 40 changes, and the change in the switching frequency can be suppressed to be relatively small.

For this reason, the disadvantages described in the section of the prior art, that is, the heat generation of the transistors 7 and 8 corresponding to the increase in the switching frequency, noise as unnecessary radiation, a decrease in efficiency, and the like are suppressed. There is no need to use a transistor with a relatively large rated current.
There is no need to make the heat dissipating fins large. In addition, a saturable reactor transformer 6 as an oscillation transformer
Therefore, various effects can be obtained such that it is not necessary to increase the thickness of the winding, and thus it is not necessary to attach a magnetic shield case having a high shielding effect to the oscillation transformer. Therefore, the configuration of the switching circuit 4 is relatively small, and as a result, the size and weight of the device can be reduced, and the cost of the device can be reduced.

In addition, by reducing the unnecessary radiation, the inductance value of a line filter, a ferrite bead, etc. (not shown) for reducing unnecessary radiation can be reduced, so that the size and cost can be further reduced. In addition, since the change in the switching frequency of the switching circuit 4 is small, the tuning of the resonance point specific to the resonance power supply system at the time of design adjustment becomes easy, and the effect of shortening the design and development time can be obtained.

In addition, since the change in the switching frequency can be suppressed, the operation itself of the switching circuit 4 is further stabilized.

It should be noted that a slight change in the voltage Vs due to a load change in the load circuit 40 can be handled by the load circuit 40. If further stabilization is required, only that portion may be stabilized by a three-terminal regulator IC or the like.

Further, the present invention is not limited to the above-described embodiment, but may adopt various configurations.

[0044]

As described above, according to the switching power supply of the present invention, the control circuit of the auxiliary load circuit is controlled by the voltage variable circuit according to the terminal voltage of the control coil of the saturable reactor transformer constituting the switching circuit. Is changed. Therefore, when the load state of the auxiliary load circuit changes, the rectified voltage for supplying the current to the auxiliary load circuit changes, and the effect of reducing the change in the switching frequency can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a configuration of a switching power supply according to a conventional technique.

[Explanation of symbols]

 Reference Signs List 4 switching circuit 11 control coil 16 saturable reactor transformer 22 rectifier circuit 24, 40 load circuit 68 voltage variable circuit Vc terminal voltage Vs rectified voltage Vref reference voltage

Claims (1)

(57) [Claims] At least a first control coil and said first control coil
A saturable reactor transformer having a drive coil whose inductance value changes in accordance with the current flowing through the control coil, and a switching element that is switched by a signal from the drive coil of the saturable reactor transformer.
A switching circuit for interrupting the supplied DC, a first resonance transformer having an output of the switching circuit supplied to the primary side, and a first resonance transformer having a second control coil; A first resonance transformer having a resonance frequency lower than a switching frequency of the switching circuit together with the first resonance transformer;
A first capacitor forming a resonance circuit of the first aspect, and a first capacitor rectifying a secondary output of the first resonance transformer.
A rectifier circuit, a main load circuit to which a rectified output of the first rectifier circuit is supplied, and an output voltage of the first rectifier circuit is detected and compared with a reference voltage. By changing the current supplied to the second control coil of the first resonance transformer,
A first control circuit that changes a resonance frequency of the first resonance circuit so that a resonance frequency of the first resonance circuit increases when an output voltage of the first rectification circuit increases. The second circuit in which the output of the switching circuit is supplied to the primary side
A second transformer that forms a resonance circuit having a resonance frequency lower than the switching frequency of the switching circuit together with the second resonance transformer; and a secondary side of the second resonance transformer. The second to rectify the output
A rectifier circuit, an auxiliary load circuit to which a rectified output of the second rectifier circuit is supplied, an auxiliary load circuit having a lighter load than the main load circuit, and detecting an output voltage of the second rectifier circuit. Then, the current supplied to the first control coil of the saturable reactor transformer of the switching circuit is changed in accordance with the comparison result to increase the output voltage of the second rectifier circuit. A second control circuit that changes the switching frequency of the switching circuit so that the switching frequency of the switching circuit becomes higher when the output of the second control circuit is detected. When the output is to increase the switching frequency of the switching circuit, a voltage variable for changing the reference voltage in a direction to suppress the increase of the switching frequency. Switching power supply device and having a road.