JP2001112254A - Power circuit - Google Patents

Abstract

(57) [Summary] In a power supply circuit of an electronic device, a snubber circuit is provided to absorb a leakage spike voltage, but power is consumed by the snubber circuit even in a standby state, thereby saving energy. Could not be planned. A switching power supply circuit in which a DC voltage is supplied to one end of a primary winding of a transformer and a switching transistor is connected to the other end, wherein the switching power supply circuit can operate in a normal operation mode or a standby mode.
Further, a snubber circuit is connected to the switching transistor in order to suppress an overvoltage applied to the switching transistor. A switching circuit for operating the snubber circuit in the normal operation mode and stopping the operation of the snubber circuit in the standby mode is provided, so that the snubber circuit works effectively during the normal operation, and suppresses power consumption by the snubber circuit during the standby mode. Things.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit in an electronic device such as a television receiver, which can operate in a normal operation mode and a standby mode, and in particular, reduces power consumption in the standby mode. Power circuit.

[0002]

2. Description of the Related Art Conventionally, switching power supply circuits have been employed in various electronic devices. The switching power supply circuit has a switching transformer and a high-speed switching element, rectifies an AC voltage from a commercial AC power supply and supplies the rectified voltage to the primary winding of the transformer, and turns on / off frequency and on time of the switching element. Is controlled to keep the output voltage obtained via the secondary winding of the transformer constant.

FIG. 3 shows an example of a conventional switching power supply circuit, and shows a ringing choke inverter type power supply circuit. In FIG. 3, a commercial AC power supply 1
Is connected to an input terminal of a full-wave rectifier circuit 3 via a power switch 2, and one output terminal of the rectifier circuit 3 is grounded via a smoothing capacitor 4. The rectifier circuit 3 and the smoothing capacitor 4 constitute a DC voltage source 5 that rectifies and smoothes an AC power supply voltage to obtain a DC voltage.

The DC voltage source 5 is connected to a ground potential through a series circuit of a primary winding 61 of a switching transformer 6 and a switching transistor 7, and the base of the transistor 7 is connected to a feedback winding 62 of the transformer 6. A voltage for turning on / off the transistor 7 is supplied from the feedback winding 62 via the resistor 8.

On the other hand, a plurality of secondary windings 63, 64, and 65 are provided on the secondary side of the transformer 6, and the magnetic energy accumulated in the transformer 6 during the on-period of the transistor 7 is converted to the secondary energy during the off-period. So that each secondary winding 6
Rectifier / smoothing circuits 91, 92 and 93 are connected to 3, 64 and 65 to obtain a DC output voltage. A power supply voltage (Vcc1) of, for example, 125 V can be obtained from the rectification / smoothing circuit 91, and this voltage (Vcc1) is supplied to the load circuit 10. A power supply voltage of, for example, 25 V can be obtained from the rectifying / smoothing circuit 92, and the power supply voltage is converted to a low voltage (for example, 5 V) power supply voltage (Vcc2) by the stabilization circuit 11 and supplied to another load circuit. Further, an appropriate power supply voltage (Vcc3) can be obtained from the rectifying / smoothing circuit 93.

Further, the power supply voltage (Vcc1) from the rectifying / smoothing circuit 91 is supplied to the base of the transistor 7 via the feedback circuit 12 and the bypass circuit 13, and the switching of the transistor 7 is performed according to the fluctuation of the secondary output voltage. The frequency and the on / off period are controlled, and the secondary side output voltage is stabilized. Therefore, the feedback circuit 12 and the bypass circuit 13 are connected to the switching control circuit 14
Is composed.

Further, the power supply circuit of FIG. 3 is operable in a normal operation mode and a standby mode based on user control. That is, the user can select a normal operation mode or a standby mode by using a remote controller (remote controller) 15, and a signal from the remote controller 15 is received by a remote controller light receiver 16 and supplied to a microcomputer (microcomputer) 17. It has become. The microcomputer 17 and the remote controller 16 are always operated by the power supply voltage (Vcc2).
By controlling the feedback circuit 12 by the control signal C1 from the control circuit 7, the switching frequency of the transistor 7 is reduced in the standby mode, and the ON period is shortened and the OFF period is lengthened.

As a result, in the standby mode, the output voltage on the secondary side can be suppressed low, and the power consumption can be reduced as compared with the normal operation. During standby, the voltage from the rectifying / smoothing circuit 92 drops to about 10 V. However, since the stabilization circuit 11 originally obtains a low-voltage (5 V) power supply voltage, the standby mode is the same as the normal operation mode. The same voltage (Vcc2) can be obtained, and this is supplied to the standby load such as the microcomputer 17.

A snubber circuit 18 is connected between the collector of the transistor 7 and the ground. The snubber circuit 18 suppresses overvoltage, and FIG. 3 shows an example in which the snubber circuit 18 is configured by a series circuit of a capacitor 19 and a resistor 20.

Next, the operation of the conventional power supply circuit will be described. When the power switch 2 is turned on, the AC voltage from the AC power source 1 is converted into a DC voltage E1 by the full-wave rectifier circuit 3 and the smoothing capacitor 4, and the primary winding 6 of the transformer 6 is turned on.
1 to the collector of the transistor 7. A base current is applied to the base of the transistor 7 by a start-up circuit (not shown), and the transistor conducts to start an oscillating operation. When the DC voltage E1 is applied to the primary winding 61 when the transistor 7 is conducting, a voltage proportional to the DC voltage E1 is induced in the feedback winding 62, and a base current is supplied to the transistor 7 by the induced voltage. By adjusting the base current by the bypass circuit 13, the transistor 7 is driven by self-excitation.

While the transistor 7 is conducting, the primary winding 6
Magnetic energy is stored in the transformer 6 by the current flowing through the transformer 1. Thereafter, when the transistor 7 is turned off, the accumulated magnetic energy is released to the secondary winding 63, and is converted into a DC voltage by the rectifying / smoothing circuit 91, so that the load 10
Output voltage Vcc1 can be obtained. When the emission of the magnetic energy is completed, the transistor 7 is turned on again, and the on / off operation is repeated thereafter.

On the other hand, the output voltage from the rectifying / smoothing circuit 91
Vcc1 is supplied to the bypass circuit 13 via the feedback circuit 12, and is used for stabilizing the output voltage. That is, the feedback circuit 12 detects the output voltage Vcc1 and supplies a control signal that changes according to the output voltage Vcc1 to the bypass circuit 13. The bypass circuit 13 acts to control the amount of bypass of the current input to the base of the transistor 7 to control the on / off period of the transistor 7, thereby making the output voltage Vcc1 constant. The rectifying / smoothing circuits 92 and 93
Is also stabilized.

On the other hand, since the transformer 6 has leakage inductance between the primary and secondary windings, when the transistor 7 is switched from on to off, 100% of the energy stored in the transformer 6 is output to the secondary side. However, since the leakage spike voltage is applied to the transistor 7 as a leakage spike voltage, the leakage spike voltage becomes an overvoltage and gives a stress to the transistor 7. Also, the leakage spike voltage contains high frequency components,
In some cases, noise was generated and adversely affected peripheral circuits.

Therefore, a snubber circuit 18 is connected between the collector of the transistor 7 and the ground potential point. The snubber circuit 18 absorbs a steep voltage component of the leakage spike voltage by the capacitor 19 and the resistor 20, and energy of the leakage spike is consumed as heat energy of the resistor 20.

FIG. 4 shows a state in which a leakage spike voltage is generated. The collector-emitter voltage Vce of the transistor is set to a value in consideration of the spike voltage.

[0016]

As described above, in the conventional power supply circuit, the leakage spike voltage is absorbed and removed by the snubber circuit 18. However, it is difficult to extract and remove only the leakage energy. To remove some useful energy, transformer 6
The energy transfer efficiency between primary and secondary is deteriorated, and power consumption is increased.

In particular, when the load on the secondary side is small as in the standby mode, the energy due to the spike voltage is small and the stress on the transistor 7 is small, so that the snubber circuit 18 is often unnecessary. Therefore, in the conventional power supply circuit, wasteful power is consumed by the snubber circuit 18 even during standby, and there is a disadvantage that energy saving cannot be achieved.

In view of the above problems, an object of the present invention is to provide a power supply circuit capable of reducing power consumption during standby in an electronic device including a snubber circuit.

[0019]

A power supply circuit according to the present invention has a DC voltage source for converting an AC power supply voltage to a DC voltage, at least a primary winding and a secondary winding, and one end of the primary winding. A transformer having the DC voltage supplied thereto and having a switching transistor connected to the other end thereof, an output voltage generating circuit including a rectifier circuit connected to the secondary winding and generating an output voltage to be supplied to a load circuit; A control circuit connected to the base of the transistor, causing the transistor to perform a switching operation in one of a normal mode and a standby mode, and controlling the output voltage to the load circuit to be lower in the standby mode than in the normal operation mode; A snubber circuit connected to the switching transistor for suppressing an overvoltage applied to the switching transistor; In work mode to operate the snubber circuit, the in standby mode is obtained by including a switching circuit for stopping the operation of the snubber circuit.

According to the present invention, the snubber circuit works effectively when the electronic device is in normal operation, and the generation of a leakage spike voltage can be prevented. When the electronic device is in the standby mode, the snubber circuit is opened and the snubber circuit is opened. Power consumption by the circuit can be suppressed.

[0021]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a power supply circuit according to an embodiment of the present invention. Note that the same components as those of the conventional power supply circuit of FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, the power supply circuit of the present invention is characterized in that a switching circuit 21 for controlling the operation of the snubber circuit 18 on and off is provided. That is, the switching circuit 2
Reference numeral 1 mainly includes a triac 22 coupled between the snubber circuit 18 and a ground potential point, and a photocoupler 23 for controlling the operation of the triac 22. The photocoupler 23 includes a photodiode 24 and a phototransistor 25. The anode of the photodiode 24 is connected to the microcomputer 17 via a resistor 26, and the cathode is grounded. The collector of the phototransistor 25 is connected to the DC voltage source 5 via the resistor 27, and the emitter is grounded.

The microcomputer 17 includes a rectifying / smoothing circuit 92
Can be always operated by the voltage Vcc1 stabilized by the stabilizing circuit 11 from the DC voltage, and the power supply circuit can be controlled to operate in the normal operation mode or the standby mode in response to the operation of the remote controller 15 by the user. is there. That is, the microcomputer 17 receives a remote control signal from the remote controller 15, outputs a high-level control signal C1 from the microcomputer 17 in the normal operation mode, and outputs a low-level control signal C1 in the standby mode, and supplies the control signal C1 to the photodiode 24 and the feedback circuit 12. Like that.

The control signal C2 is output from the microcomputer 17 to enable the load circuit 10 to be controlled. When the load circuit 10 is, for example, a deflection circuit of a television receiver, control is performed so that the operation of the deflection circuit is stopped in the standby mode. Alternatively, the operation of not only the deflection circuit but also other load circuits may be stopped as needed.
Although the rectifying / smoothing circuit 93 in FIG. 3 is not shown in FIG. 1, the rectifying / smoothing circuit 93 may be provided in FIG. 1 as in FIG.

Next, the operation of the power supply circuit of the present invention shown in FIG. 1 will be described.

When the power supply switch 2 is turned on, the AC voltage from the AC power supply 1 is converted into a DC voltage E1 by the full-wave rectifier circuit 3 and the smoothing capacitor 4, and the voltage of the transistor 7 is Supplied to the collector. In the normal operation mode, the transistor 7 repeats the on / off operation at a high speed, and the magnetic energy stored in the transformer 6 during the on period of the transistor 7 is released to the secondary winding 63 during the off period of the transistor 7 to rectify. The load 10 is converted into a DC voltage by the smoothing circuit 91 and
Output voltage Vcc1 (for example, 125 V) for driving.

On the other hand, the feedback circuit 12 receives the high-level control signal C 1 from the microcomputer 17 and supplies a control signal that changes according to the output voltage Vcc 1 to the bypass circuit 13.
The bypass circuit 13 acts to control the amount of bypass of the current input to the base of the transistor 7 to control the on / off period of the transistor 7, thereby making the output voltage Vcc1 constant.

In normal operation, a high-level control signal C1 is output from the microcomputer 17 and supplied to the photodiode 24, so that the photodiode 24 and the phototransistor 25 conduct, and a current flows through the gate of the triac 22, The triac 22 is turned on. As a result, the snubber circuit 18 is connected between the collector of the transistor 7 and the ground potential point, thereby absorbing the leakage spike voltage and effectively performing the overvoltage protection operation.

When the standby mode is selected by the user operating the remote controller 15, a signal from the remote controller 15 is received by the remote controller light receiver 16 and supplied to the microcomputer 17. In response, the microcomputer 17 outputs a low-level control signal C1 to control the feedback circuit 12 to lower the switching frequency of the transistor 7 and to shorten the on-period and lengthen the off-period. .
Thus, in the standby mode, the output voltage on the secondary side can be kept low, and the power consumption can be reduced as compared with the normal mode.

Further, in the standby mode, since the control signal C1 supplied to the anode of the photodiode 24 becomes low level, the photodiode 24 and the phototransistor 25 become non-conductive, and current is supplied to the gate of the triac 22. However, the triac 22 is also turned off. Therefore, the snubber circuit 18 is disconnected, and the power consumed by the snubber circuit 18 in the standby mode can be eliminated. In the standby mode, since the energy due to the spike voltage is small and the stress on the transistor 7 is small, there is no particular problem even if the operation of the snubber circuit 18 is stopped.

Although the voltage from the rectifier / smoothing circuit 92 drops to about 10 V during standby, the stabilizing circuit 11 originally obtains a low voltage (5 V) power supply voltage. The same voltage (Vcc2) as in the mode can be obtained, and this is supplied to the standby load such as the microcomputer 17.

Next, a second embodiment of the present invention will be described with reference to FIG.

In FIG. 2, the same components as those of the power supply circuit of FIG. 1 are denoted by the same reference numerals, and detailed description will be omitted.

FIG. 2 is characterized in that another snubber circuit 31 is used in place of the snubber circuit 18 of FIG. That is, the snubber circuit 31 is composed of a parallel circuit of a resistor 32 and a capacitor 33. One end of the parallel circuit is connected to the DC voltage source 5, and the other end of the parallel circuit is connected to the collector of the transistor 7 via the cathode and anode of the thyristor 34. Connected to The thyristor 34 constitutes a switching circuit 35 together with the photocoupler 23, and connects the emitter of the phototransistor 25 to the gate of the thyristor 34.

Next, particularly the snubber circuit 31 of the power supply circuit of FIG.
The operation of will be described. In FIG. 2, during normal operation, a high-level control signal C1 is supplied from the microcomputer 17 to the anode of the photodiode 24, and the photodiode 24 and the phototransistor 25 are turned on. As a result, a current flows through the gate of the thyristor 34, the thyristor 34 conducts, and the snubber circuit 31 formed by the parallel circuit of the resistor 32 and the capacitor 33 is connected between the primary windings of the transformer 6, reducing the leakage spike voltage. Absorb and work effectively.

When the standby mode is selected by the user operating the remote controller 15, the photodiode 24
Since the control signal C1 supplied to the anode of the thyristor becomes low level, the photodiode 24 and the phototransistor 25 become non-conductive, and no current is supplied to the gate of the thyristor 34, and the thyristor 34 is turned off. Therefore, snubber circuit 3
1 is disconnected, and the power consumed by the snubber circuit 31 in the standby mode can be eliminated.

The switching circuits 21 and 35 for controlling the operations of the snubber circuits 18 and 31 are not limited to the examples shown in FIGS.

As described above, according to the power supply circuit of the present invention, the snubber circuit works effectively when the electronic device operates normally, and the generation of the leakage spike voltage can be prevented. Further, when the electronic device is in the standby mode, the snubber circuit is opened, and the power consumption consumed by the snubber circuit can be eliminated. According to experiments, the standby power of the present invention was reduced to 6 W or less, compared to the conventional standby power of 8 W.

[0040]

As described above, according to the present invention, the snubber circuit works effectively during normal operation of the electronic device, thereby preventing generation of leakage spike voltage and reducing unnecessary radiation noise which adversely affects peripheral circuits. In addition, when the electronic device is in the standby mode, the snubber circuit is opened, so that power consumption can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a power supply circuit according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional power supply circuit.

FIG. 4 is a voltage waveform diagram showing a generation state of a leakage spike voltage generated in the power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Power switch 5 ... DC voltage source 6 ... Transformer 7 ... Switching transistor 91,92 ... Rectification / smoothing circuit 10 ... Load circuit 11 ... Stabilization circuit 14 ... Switching control circuit 17 ... Microcomputer 18,31 ... Snubber circuits 21, 35 Switching circuit 22 Triac 23 Photocoupler 34 Thyristor

Claims (3)

[Claims] 1. A DC voltage source for converting an AC power supply voltage into a DC voltage, and at least a primary winding and a secondary winding, wherein one end of the primary winding is supplied with the DC voltage and the other end is a switching transistor. And a rectifier circuit connected to the secondary winding, and an output voltage generation circuit that generates an output voltage to be supplied to a load circuit. And a control circuit that controls the output voltage to the load circuit in the standby mode to be lower than that in the normal operation mode, and suppresses an overvoltage applied to the switching transistor. Therefore, the snubber circuit connected to the switching transistor and the snubber circuit operate in the normal operation mode. Is allowed, the in standby mode power supply circuit, characterized by comprising a switching circuit for stopping the operation of the snubber circuit. 2. The power supply circuit according to claim 1, wherein said snubber circuit comprises a series circuit of a resistor and a capacitor connected between a collector of said switching transistor and a ground potential point. 3. The power supply circuit according to claim 1, wherein said snubber circuit comprises a parallel circuit of a resistor and a capacitor connected between one end of a primary winding of said transformer and a collector of said switching transistor.