JP3244424B2 - Power circuit - Google Patents

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, and more particularly, to improvement of a two-system power supply circuit for generating two kinds of power supply voltages.

[0002]

2. Description of the Related Art A conventional two-system power supply circuit will be described below with reference to the drawings. This circuit is used, for example, in a device such as a color television which requires a high-voltage power supply voltage used for a cathode ray tube or the like and a low-voltage power supply voltage used for other circuits and the like, and two types of power supply voltages. The power supply circuit is used when one power supply circuit supplies such two types of power supply voltages.

As shown in FIG. 5, this circuit includes a first voltage generator (1) for outputting a first output voltage (Vo1).
And a second voltage generator (2) for outputting a second output voltage (Vo2). The first voltage generation unit (1) includes a first switch transistor (TR10)
A first control unit (IC10) for controlling on / off of the
A first switch transistor (T
R10), a first transformer (T10), and a secondary coil (Ns) of the first transformer (T10).
The electromotive force induced on the secondary side is rectified to produce a first output voltage (V
o1), a first rectifier circuit (3) that constantly generates the first output voltage (Vo1), and a first controller (IC1).
0) and a photocoupler (PC10) for transmitting this.

A second voltage generator (2) includes a second controller (IC20) for controlling on / off of a second switch transistor (TR20), and a second transformer (T20).
Supply / non-supply current to the primary coil (Np)
Is wound concentrically with the switch transistor (TR20) and the primary coil (Np) of the second transformer (T20),
An auxiliary winding (ND) for generating a power supply voltage for the first and second control units (IC10, IC20), a resistor (R1), a resistor (R2), a diode (D2), and a second transformer (T
20) and a second transformer connected to the secondary coil (Ns) of the second transformer (T20) and rectifying the electromotive force induced on the secondary side to generate a second output voltage (Vo2). A rectifier circuit (4), a switch circuit (SW210) for supplying / non-supplying the second output voltage (Vo2), and an on / off state of the switch circuit (SW210) are detected, and the first control unit ( Photocoupler (PC) that transmits this to IC10)
20).

The operation of this circuit will be described below.
According to this circuit, first, at the time of startup immediately after the power is turned on, the rectified AC voltage (Vin) is supplied from the bridge circuit (D10) to the first and second voltage generation units (1, 2). You. Next, this voltage (Vin) is stepped down by the resistor (R1), and the first and second control units (IC10, IC2
0) are supplied to the power supply input terminals (Vcc1, Vcc2). Since a capacitor (C2) is connected to these terminals, the potential of these terminals (Vcc1, Vcc2) rises with a time constant determined by R1C2, and the operation starts when the respective operation start voltages are reached. Then, the first and second switch transistors (TR10, TR20) are turned on / off. After the above-mentioned circuit is started, a current is supplied to the first and second transformers (T10, T20) to generate an electromotive force, which is rectified by the first and second rectifier circuits (3, 4) to produce the first and second transformers. 1, a second output voltage (Vo1, Vo2) is generated.

After starting, after the circuit operation is stabilized, an auxiliary winding (N) concentrically wound with the second transformer (T20) is used.
An electromotive force is induced in D), which is a diode (D2),
The voltage is smoothed by a resistor (R2) and a capacitor (C2), and is supplied as a power supply voltage to first and second control units (IC1, IC2). In the above circuit, the first
When it is desired to turn off the output voltage (Vo1), the switch circuit (SW210) is turned on. When this is turned on, the photodiode of the photocoupler (PC20) emits light, the phototransistor of the photocoupler (PC20) is turned on, the first control unit (IC10) is forcibly turned off, and the first output is output. The supply of the voltage (Vo1) is stopped.

[0007]

However, in the above circuit, at the time of starting, the resistance (R1) is changed to the first and the first.
The reduced voltage is supplied to the second control units (IC10, IC20) as these power supply voltages, and a current must be supplied to both of them. Requires that the resistance value of the resistor (R1) defining the time constant at the time of startup be halved. In this case, the power loss at startup is doubled,
Also, the rise order could not be set due to the difference between the operation start voltages of the first and second control units (IC10, IC20).

Further, a total of two photocouplers (PC1) are provided in the first voltage generator (1) and the second voltage generator (2).
0, PC20), which increases the manufacturing cost,
In addition, since the photocoupler (PC20) cannot be driven unless the second output voltage (Vo2) is output, there arises a problem that the first output voltage (Vo1) cannot be turned off from the secondary side. Was.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional disadvantages. As shown in FIG. 1, a first voltage generator for generating a first output voltage and a second voltage generator for generating a first output voltage are provided. A second voltage generator for generating an output voltage, wherein the first voltage generator is connected to a first transformer and a primary side of the first transformer, and a primary side of the transformer A first control unit that controls a current supply state to the coil; and a first control unit that is connected to a secondary side of the first transformer and rectifies an electromotive force induced on a secondary side of the first transformer to perform a rectification. A first rectifier circuit that generates one output voltage, and a photocoupler that constantly detects the first output voltage and feeds back the first output voltage to the first controller.
The second voltage generator includes a second transformer and the second transformer.
A second control unit that is connected to a primary side of a transformer of the second transformer and controls a current supply state to a primary coil of the second transformer; and a second control unit that is connected to a secondary side of the second transformer, A second rectifier circuit for rectifying an electromotive force induced on a secondary side of the second transformer to generate a second output voltage; and a coil wound concentrically with a primary coil of the second transformer and activated. An auxiliary winding for generating a power supply voltage of the first and second control units later, and a power supply voltage input terminal of the second control unit and a power supply voltage input terminal of the first control unit. During the second
A power supply circuit characterized in that a switching circuit that is turned on when the potential of the power supply voltage input terminal of the control unit rises above a predetermined potential is provided, as shown in FIG.
A first voltage generator that generates a first output voltage; and a second voltage generator that generates a second output voltage, wherein the first voltage generator includes a first transformer, A first control unit connected to a primary side of the first transformer and controlling a current supply state to a primary coil of the transformer, and a first control unit connected to a secondary side of the first transformer; A first rectifier circuit for rectifying an electromotive force induced on a secondary side of the first transformer to generate a first output voltage; and a first control unit that constantly detects the first output voltage and outputs the first output voltage. The second voltage generator is connected to a second transformer and a primary side of the second transformer, and the second voltage generator is connected to a primary side of the second transformer.
A second control unit for controlling the state of current supply to the primary coil of the transformer, and a starter connected to the secondary side of the second transformer and induced on the secondary side of the second transformer. A second rectifier circuit for rectifying electric power to generate a second output voltage; and a power supply voltage of the first and second control units, which is wound concentrically with a primary coil of the second transformer and is activated after starting. And a phototransistor of the photocoupler is connected to the first control unit, a photodiode of the photocoupler is connected to an output of the first rectifier circuit, A rectifier circuit, a resistor and a diode are connected in series between an output terminal of a second output voltage and a terminal on a high potential side of the photodiode, and a terminal on a low potential side of the photodiode; 2 of the rectifier circuit,
A power supply circuit is provided between the terminal on the ground side and a switch circuit for controlling on / off of the first output voltage from the secondary side, and as shown in FIG. A first voltage generator that generates a second output voltage, and a second voltage generator that generates a second output voltage, wherein the first voltage generator includes a first transformer, 1 of 1 transformer
A first control unit connected to the secondary side and controlling a current supply state to a primary coil of the transformer; and a secondary control unit connected to the secondary side of the first transformer and A first rectifier circuit that rectifies the electromotive force induced on the side to generate a first output voltage, and a photocoupler that constantly detects the first output voltage and feeds it back to the first controller. The second voltage generator is connected to a second transformer and a primary side of the second transformer, and controls a current supply state to a primary side coil of the second transformer. A second control unit connected to a secondary side of the second transformer and rectifying an electromotive force induced on the secondary side of the second transformer to generate a second output voltage; A rectifier circuit is wound concentrically with the primary coil of the second transformer, and after starting, the first and second control units An auxiliary winding for generating a supply voltage parts, and the second power supply voltage input terminal of the control unit, between the power source voltage input terminal of said first controller, said second
A switching circuit that is turned on when the potential of the power supply voltage input terminal of the control unit rises above a predetermined potential, wherein the phototransistor of the photocoupler is the first transistor.
And the photodiode of the photocoupler is connected to the output of the first rectifier circuit,
A rectifier circuit, a resistor and a diode are connected in series between an output terminal of a second output voltage and a terminal on a high potential side of the photodiode, and a terminal on a low potential side of the photodiode; A switch circuit for controlling on / off of the first output voltage from a secondary side is provided between the rectifier circuit and the ground terminal of the second rectifier circuit. Is the solution.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a power supply circuit according to an embodiment of the present invention will be described with reference to the drawings. (1) First Embodiment This circuit has two types of power supply voltage, such as a high-voltage power supply voltage used for a cathode-ray tube, such as a color television, and a low-voltage power supply voltage used for other circuits. The power supply circuit is used for a device that requires the above-described power supply voltage, and is used when one of the two power supply voltages is supplied by one power supply circuit.

As shown in FIG. 1, the circuit includes a first voltage generator (11) for outputting a first output voltage (Vo1).
A second voltage generator (12) that outputs a second output voltage (Vo2); and a switching unit provided between the second voltage generator (12) and the first voltage generator (11). A circuit (13). The configuration of each unit will be described below.

As shown in FIG. 1, the first voltage generator (11) includes a first controller (IC1), a first switch transistor (TR1), a first transformer (T1), 1 rectifier circuit (14) and a photocoupler (PC1). The first control unit (IC1) is an IC that controls on / off of the first switch transistor (TR1).

First switch transistor (TR1)
Is a primary coil (N) of a first transformer (T1) described later.
This is an NPN transistor that supplies / non-supplies the current to p1). The first rectifier circuit (14) includes a diode (D1
1) and a capacitor (C11), which is connected to the secondary coil (Ns1) of the first transformer (T1),
It rectifies the electromotive force induced on the secondary side to generate a first output voltage (Vo1). And the photocoupler (PC1) constantly detects the first output voltage (Vo1) and transmits it to the first control unit (IC1).

As shown in FIG. 1, the second voltage generator (12) includes a second controller (IC2), a second switch transistor (TR2), a second transformer (T2),
A second rectifier circuit (15). The second control unit (I
C2) is a second switch transistor (TR
This is an IC that controls on / off of 2).

Second switch transistor (TR2)
Is the primary coil (Np2) of the second transformer (T2)
Is an NPN transistor that supplies / non-supplies a current to the NPN transistor. The auxiliary winding (Nd) is connected to one of the second transformers (T2).
It is wound concentrically with the secondary coil (Np2) and generates a power supply voltage for the first and second control units (IC1, IC2).

A diode (D2) and a capacitor (C
2) The resistor (R2) forms a smoothing circuit for smoothing the voltage of the auxiliary winding (ND). In the present embodiment, the resistance value of the resistor (R2) is smaller than that of the related art. The reason will be described later. The second rectifier circuit (15)
It is connected to the secondary coil (Ns2) of the second transformer (T2) and rectifies the electromotive force induced on the secondary side to generate a second output voltage (Vo2).

The switching circuit (13) is a characteristic part of the power supply circuit according to the present embodiment, and includes a power supply voltage input terminal (Vcc2) of the second control unit (IC2) and the first circuit.
And a power supply voltage input terminal (Vcc1) of the control unit (IC1), a Zener diode (ZD31), resistors (R33, R34), and an NPN transistor (TR3).
2) It is composed of a PNP transistor (TR31).

This circuit turns on the PNP transistor (TR31) when the potential of the power supply voltage input terminal (Vcc2) of the second control unit (IC2) rises above a predetermined potential, thereby turning on the auxiliary winding (ND). ) To the first
To the power supply voltage input terminal (Vcc1) of the control unit (IC1). The circuit according to the present embodiment does not include the switch circuit (SW210) for supplying / non-supplying the second output voltage (Vo2).
0) is detected, and the first control unit (IC
1) is different from the prior art in that it does not have a photocoupler (PC20) for transmitting the signal to 1) and that it has the above-described switching circuit (13).

The operation of this circuit will be described below.
According to this circuit, first, power is turned on, and the rectified AC voltage (Vin) is supplied from the bridge circuit (D1) to the first and second voltage generators (11, 12). Next, this voltage (Vin) is stepped down by the resistor (R1),
Is output to the power input terminal (Vcc2) of the control unit (IC2). At this time, unlike the conventional case, the switching transistor (TR31) of the switching circuit (13) is turned off.
Since the voltage is not N, the reduced voltage is not supplied to the power supply input terminal (Vcc1) of the first control unit (IC1). Therefore, the current flowing through the resistor (R1) is 1
/ 2.

A capacitor (C) is connected to this terminal (Vcc2).
2) is connected, the potential of the power supply input terminal (Vcc2) rises with a time constant determined by R1C2, and when the voltage reaches the operation start voltage of the second control unit (IC2), the operation starts. To turn on / off the second switch transistor (TR2). With this, 1 of the second transformer (T2)
A current is supplied to the secondary coil, transmitted to the secondary coil, and rectified by the second rectifier circuit (15), whereby a second output voltage (Vo2) is output.

At this time, when a magnetic field is generated in the primary coil, an induced electromotive force is induced in the auxiliary winding (Nd) and smoothed by the diode (D2), the capacitor (C2), and the resistor (R2). Later, the second control unit (IC
2) The potential of the power input terminal (Vcc2) rises. When the potential of the power supply input terminal (Vcc2) rises and finally exceeds the Zener voltage of the Zener diode (ZD31), this conducts and the transistor (TR32) turns ON.
Zener diode (ZD31) → base of transistor (TR32) → emitter → ground potential (GND)
Current flows through the path, and the transistor (TR31) is turned on.

For the first time in this way, the auxiliary winding (Nd)
The induced electromotive force is input to the power input terminal (Vcc1) of the first control unit (IC1), and the first control unit (IC1) is activated. First control unit (IC
After the activation of 1), current is supplied to the primary coil of the first transformer (T1), and the current is supplied by the first rectifier circuit (14) connected to the secondary side of the first transformer (T1). After being rectified, it is output as a first output voltage (Vo1).

As described above, the switching circuit (13) newly added in the present embodiment includes a second control unit (IC
After the 2) completely starts up, the first control unit (IC1)
Supplies the power supply voltage to the first voltage generator (1).
1) is such that it does not rise until after the second voltage generation unit (12) has risen, and unlike the conventional case where it is uncertain which one rises first, the start order is defined in this way. It becomes possible to do.

Actually, as described above, the first output voltage (Vo1) is a high-voltage power supply voltage for a cathode ray tube,
Since the second output voltage (Vo2) is a power supply voltage related to other circuits, considering the order of use, the start-up order is the first output voltage after the second output voltage (Vo2) rises.
It is desirable to raise the output voltage (Vo1) of
By adding the switching circuit (13),
It is possible to reliably define the order of such activation.

Further, as described above, at the time of startup, unlike the conventional case, the power supply input terminal (V) of the first control unit (IC1)
cc1) is not supplied with the voltage stepped down by the resistor (R1), and no current flows to the first control unit (IC1) side. Therefore, the current flowing through the resistor (R1) is reduced to half that of the conventional circuit. Become. Therefore, there is also an effect that the loss of power consumption at the time of starting can be reduced.

By the way, unlike the conventional circuit, in the circuit according to the present embodiment, the ON / OF of the second voltage generator (12) is turned on.
There is no second photocoupler for transmitting the F state to the first control unit (IC1). This is because the load current (Io2) flowing through the load of the second voltage generator (12) can be detected on the primary side, and the details will be described below.

FIG. 2 is a graph for explaining the relationship between the change in the load current due to the magnitude of the resistance (R2) and the change in the potential (potential of Vcc2) at point A in FIG. In the above circuit,
When the resistance (R2) is large, the potential at the point A in FIG. 1 does not fluctuate so much as the load current fluctuates as shown in FIG. 2, so that the resistance was conventionally increased in order to stably operate.

On the other hand, it is experimentally known that when the resistance value is reduced, the potential at the point A changes in proportion to the change in the load current, as shown in FIG. In the present invention, this fact is reversed, and the value of the resistor (R2) is reduced, so that the potential at the point A is intentionally fluctuated in accordance with the increase or decrease of the load current (Io2). Since the potential at the point A increases as the load current (Io2) increases, it has been found that it is possible to know the state of the load current (Io2) on the primary side using this during normal operation.

According to the circuit according to the present embodiment, since the switching circuit (13) is provided, by adjusting the voltage at which the switching circuit (13) is turned on (this is to change the constant of the circuit element). In the case where the second output current (Io2) falls below a certain amount, the switching circuit (13) is turned off.
F, the supply of the power supply voltage to the first control unit (IC1) is stopped, and the first output voltage (Vo1) can be turned off. Therefore, the first control unit (IC1) is turned off by the control on the secondary side, and the first output voltage (Vo) is turned off.
Turning off 1) can be realized by lowering the load current (Io2).

(2) Second Embodiment A power supply circuit according to a second embodiment of the present invention will be described below. Descriptions of items common to the first embodiment will be omitted to avoid duplication. This embodiment is the first
The difference between the first embodiment and the second embodiment is that the first embodiment does not include the switching circuit (13), which is a feature of the first embodiment, and outputs the first voltage generation unit (from the output terminal of the second output voltage (Vo2) 11) A resistor (R21) and a diode (D3) are directed toward one end of the photodiode of the photocoupler (PC1).
2) are connected in series, and a switch circuit (SW21) is connected between the other end of the photodiode of the photocoupler (PC1) and the ground potential (GND) of the secondary-side second voltage generator (12). ) Is provided. The other configuration is the same as that of the first embodiment, and the description is omitted.

The operation of the above circuit will be described below.
When the circuit is started, the power is turned on and the AC voltage (V) rectified from the bridge circuit (D1) as in the prior art.
in) is supplied to the first and second voltage generators (11, 12). Next, the voltage (Vin) is stepped down by the resistor (R1) and output to the power input terminals (Vcc1, Vcc2) of the first and second control units (IC1, IC2). Since a capacitor (C2) is connected to these terminals, these terminals (V) have a time constant determined by R1 and C2.
The potentials of the first and second switch transistors (TR1, TR2) are turned on / off when the potentials of the first and second switch transistors (TR1, TR2) rise and reach the respective operation start voltages. After the circuit is activated and stabilized, a current is supplied to the first and second transformers (T10, T20) to generate an electromotive force, and the first and second rectifier circuits (14, 15) generate the electromotive force. Rectification is performed to generate first and second output voltages (Vo1, Vo2).

According to the circuit of this embodiment, as shown in FIG. 3, the output terminal of the second output voltage (Vo2) is connected to the photodiode of the photocoupler (PC1) of the first voltage generator (11). A resistor (R21) and a diode (D32) are connected in series toward one end.
A switch circuit (SW21) is provided between the other end of the photodiode of 1) and the ground potential (GND) of the secondary-side second voltage generator (12).

Conventionally, the photocoupler (PC20) required for the second voltage generator is replaced with the second output voltage (Vo2).
The ON / OFF state of the first control unit (IC1)
However, in the circuit of the present embodiment, the second voltage generator (12) is not provided with a photocoupler for this purpose, and the first voltage generator (11)
A photocoupler (PC1) provided for controlling the output voltage by transmitting the voltage on the secondary side to the primary side changes the ON / OFF state of the second output voltage (Vo2) to the first control unit ( IC1) is also used as a photocoupler for transmission.

That is, the second output voltage (Vo2) is changed to O
To perform FF, the second voltage control unit (12)
ON the switch circuit (SW21) provided on the secondary side of
do it. Then, the potential of one end of the photodiode of the photocoupler (PC1) decreases to the ground potential (GND), and the potential of the other end changes to the resistance (R21) and the diode (D1).
32) are connected in series, the photodiode emits light, the phototransistor of the photocoupler (PC1) is turned on, the first control unit (IC10) is forcibly turned off, and the first output voltage ( The supply of Vo1) is stopped.

Thus, the ON / OFF state of the second output voltage (Vo2) is sent to the first control unit (11) by the photocoupler (PC1) provided on the first voltage generation unit (11) side. Since the signal can be transmitted, the photocoupler on the second voltage generation unit (12) side, which is conventionally required for this purpose, becomes unnecessary. Therefore, the number of components can be reduced by the amount of the photocoupler, and the manufacturing cost can be reduced.

(3) Third Embodiment A power supply circuit according to a third embodiment of the present invention will be described below with reference to the drawings. In addition, description of items common to the first and second embodiments will be omitted to avoid duplication. This embodiment is different from the first and second embodiments in the configuration in that a diode (D32) connected in series, which is added to the circuit of the first embodiment in the second embodiment,
The point where the resistance (R21) is added, that is, from the output terminal of the second output voltage (Vo2) to the first voltage generation unit (1
A resistor (R21) and a diode (D32) are connected in series to one end of the photodiode of the photocoupler (PC1) of 1), and the other end of the photodiode of the photocoupler (PC1) and the second end of the secondary side are connected. 2 voltage generator (12)
Between the switch circuit (SW2) and the ground potential (GND) of the
1) is provided, that is, it can be said that the circuit is a combination of the circuit of the first embodiment and the circuit of the second embodiment. The configuration and function of each unit are the same as those of the first and second embodiments, and thus the description is omitted.

The operation of the above circuit will be described below.
The operation at the time of startup is the same as that of the first embodiment. First, the power is turned on, and the AC voltage (Vin) rectified from the bridge circuit (D1) is supplied to the first and second voltage generators (11, 12). Next, this voltage (Vi
n) is reduced by the resistor (R1), and the second control unit (I
It is output to the power input terminal (Vcc2) of C2). At this time, unlike the related art, since the switching transistor (TR31) of the switching circuit (13) is not ON, the power supply input terminal (Vcc) of the first control unit (IC1) is used.
This reduced voltage is not supplied to 1).

Accordingly, the current flowing through the resistor (R1) is also reduced to half that of the conventional circuit. Since the capacitor (C2) is connected to this terminal (Vcc2), the potential of the terminal (Vcc2) rises with the time constant determined by R1 and C2,
When the voltage reaches the operation start voltage of the control unit (IC2) of the second switch transistor (TR2)
Is turned on / off. As a result, current is supplied to the primary coil of the second transformer (T2), transmitted to the secondary coil, and rectified by the second rectifier circuit (15).
Is output voltage (Vo2).

At this time, when a magnetic field is generated in the primary coil, an induced electromotive force is induced in the auxiliary winding (Nd) and smoothed by the diode (D2), the capacitor (C2), and the resistor (R2). Later, the second control unit (IC
2) The potential of the power input terminal (Vcc2) rises. When the potential of the power supply input terminal (Vcc2) rises and finally exceeds the Zener voltage of the Zener diode (ZD31), this conducts and the transistor (TR32) turns ON.
Zener diode (ZD31) → base of transistor (TR32) → emitter → ground potential (GND)
Current flows through the path, and the transistor (TR31) is turned on.

For the first time in this way, the auxiliary winding (Nd)
The induced electromotive force is input to the power input terminal (Vcc1) of the first control unit (IC1), and the first control unit (IC1) is activated. First control unit (IC
After the activation of 1), current is supplied to the primary coil of the first transformer (T1), and the current is supplied by the first rectifier circuit (14) connected to the secondary side of the first transformer (T1). After being rectified, it is output as a first output voltage (Vo1).

As described above, the switching circuit (13) newly added in the present embodiment includes a second control unit (IC
After the 2) completely starts up, the first control unit (IC1)
Supplies the power supply voltage to the first voltage generator (1).
1) is such that it does not rise until after the second voltage generator (12) has risen, and it is possible to define the order of activation by this.

Actually, as described above, the first output voltage (Vo1) is a high-voltage power supply voltage for a cathode ray tube,
Since the second output voltage (Vo2) is a power supply voltage related to other circuits, considering the order of use, the start-up order is the first output voltage after the second output voltage (Vo2) rises.
It is desirable to raise the output voltage (Vo1) of
By adding the switching circuit (13),
Such an order of starting can be easily performed.

Further, as described above, at the time of startup, unlike the conventional case, the power input terminal (V) of the first control unit (IC1)
cc1) is not supplied with the voltage stepped down by the resistor (R1), and no current flows to the first control unit (IC1) side. Therefore, the current flowing through the resistor (R1) is reduced to half that of the conventional circuit. Become. Therefore, there is also an effect that the loss of power consumption at the time of starting can be reduced.

The first and second voltage generators (11, 1
2) is activated and the first and second output voltages (Vo1, Vo1)
After 2) is output stably, the operation is almost the same as that of the first embodiment. According to the circuit according to the present embodiment, since the switching circuit (13) is provided, by adjusting the ON voltage of the switching circuit (13) (this can be easily performed by changing the constant of the circuit element). Can be adjusted), the second output current (Io2)
When the voltage falls below a certain amount, the switching circuit (13) is turned off to stop supplying the power supply voltage to the first control unit (IC1), and the first output voltage (Vo1) is turned off. This is similar to the first embodiment in that

However, in the present embodiment, unlike the first embodiment, since the switch circuit (SW21) is provided, by turning it on / off, the first output voltage (Vo1) is turned on / off. The state can be controlled. In the circuit of the first embodiment, since the switching circuit (13) is turned on / off by a decrease in the load current, it cannot be turned on / off unless the load current (second output current (Io2)) is reduced. Although it was not possible to turn ON / OFF without changing the load current, in the present embodiment, even when it is not desired to change the load current, the switch circuit (SW21) is used to turn OFF.
To turn off the first output voltage (Vo1).
It becomes possible to do.

In the first to third embodiments, 2
Although the power supply circuit of a color television has been described as an example of the power supply circuit of the system, the present invention is not limited to this, and the same effects can be obtained even when the power supply circuit is used for a display of a computer.

[0047]

As described above, the first embodiment according to the present invention is described.
According to the power supply circuit of the first aspect, the potential of the power supply voltage input terminal of the second control unit is set to the predetermined potential between the power supply voltage input terminal of the second control unit and the power supply voltage input terminal of the first control unit. Since the switching circuit that is turned on when the voltage rises beyond the threshold value is provided, it is possible to make the first control unit start up after the second control unit starts up at startup.

Also, unlike the conventional circuit, the switching circuit is turned on after the second control unit has completely started up and the auxiliary winding has been supplied with the power supply voltage of the first and second control units. Therefore, current consumption at the time of startup can be reduced as compared with the related art in which current is supplied to the first and second control units at the time of startup and these are started up. Further, since the switching circuit is turned off when the load current decreases, the power to the first control unit can be cut off by adjusting the load current, and the first output voltage can be turned off.

According to the second power supply circuit of the present invention,
The phototransistor of the first photocoupler is connected to the first control unit, and the photodiode of the photocoupler is connected to the first control unit.
Of the second rectifier circuit is connected to the output of the second rectifier circuit.
A resistor and a diode are connected in series between a terminal at which the output voltage of the photodiode is output and a terminal on the high potential side of the photodiode, and a terminal on the low potential side of the photodiode and the ground potential of the second rectifier circuit. Is provided between the terminal and the terminal that regulates the second output voltage and the first output voltage from the secondary side, so that when the switch circuit is turned off, the first rectifier is turned off. The photodiode connected to the output of the circuit emits light, and the phototransistor on the primary side of the first transformer is turned on to stop the operation of the first control unit.

Thus, the ON / O of the second output voltage is controlled by the photocoupler provided on the first voltage generation unit side.
Since the FF state can be transmitted to the first control unit,
The photocoupler on the side of the second voltage generator, which is conventionally required for this purpose, becomes unnecessary. Therefore, the number of components can be reduced by the number of photocouplers. Furthermore, according to the third power supply circuit of the present invention, the above two circuits are combined, and in addition to the first power supply circuit of the present invention, the first photocoupler connected to the first control unit A phototransistor, a photodiode of a photocoupler connected to the output of the first rectifier circuit, a terminal of the second rectifier circuit for outputting a second output voltage, and a terminal on the high potential side of the photodiode. Provided between the resistor and the diode connected in series between the terminal, the terminal on the low potential side of the photodiode, and the terminal for defining the ground potential of the second rectifier circuit.
A switch circuit for controlling on / off of the second output voltage and the first output voltage from the secondary side;

For this reason, in the first power supply circuit, the switching circuit did not turn off unless the load current was reduced. Therefore, in order to turn off the first control unit from the secondary side, the second output voltage side However, in the third power supply circuit, the second output voltage and the first
Since the switch circuit for controlling the on / off of the output voltage from the secondary side is provided, not only the operation and effect described in the first power supply circuit can be obtained, but also the switch circuit from the secondary side without changing the load current. 1 can be turned off.

[Brief description of the drawings]

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

FIG. 2 is a graph illustrating a relationship between a load current Io and a potential of a power supply voltage input terminal Vcc2 of a second control unit according to the embodiment of the present invention.

FIG. 3 is a circuit diagram of a power supply circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a power supply circuit according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram of a power supply circuit according to a conventional example.

[Explanation of symbols]

 (11) First voltage generator (12) Second voltage generator (13) Switching circuit (14) First rectifier circuit (15) Second rectifier circuit (IC1) First controller (IC2) Second control unit (PC1) Photocoupler (T1) First transformer (T2) Second transformer (Vo1) First output voltage (Vo2) Second output voltage (SW21) Switch circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28

Claims (3)

(57) [Claims] A first voltage generation unit that generates a first output voltage; and a second voltage generation unit that generates a second output voltage. A first transformer, a first controller connected to a primary side of the first transformer, and controlling a current supply state to a primary coil of the transformer; a secondary side of the first transformer A first rectifier circuit connected to the first transformer to rectify the electromotive force induced on the secondary side of the first transformer to generate a first output voltage; and A photocoupler that feeds back to a first control unit, wherein the second voltage generation unit is connected to a second transformer and a primary side of the second transformer, and is connected to a first side of the second transformer. A second control unit for controlling a current supply state to a secondary coil; and a second control unit connected to a secondary side of the second transformer. A second rectifier circuit for rectifying the electromotive force induced on the secondary side of the second transformer to generate a second output voltage; and winding concentrically with a primary coil of the second transformer. An auxiliary winding for generating a power supply voltage of the first and second control units after activation; and a power supply voltage input terminal of the second control unit;
A switching circuit that is turned on when the potential of the power supply voltage input terminal of the second control unit rises above a predetermined potential between the control unit and the power supply voltage input terminal of the second control unit. Power circuit. 2. A power supply, comprising: a first voltage generator configured to generate a first output voltage; and a second voltage generator configured to generate a second output voltage. A first transformer, a first controller connected to a primary side of the first transformer, and controlling a current supply state to a primary coil of the transformer; a secondary side of the first transformer A first rectifier circuit connected to the first transformer to rectify the electromotive force induced on the secondary side of the first transformer to generate a first output voltage; and A photocoupler that feeds back to a first control unit, wherein the second voltage generation unit is connected to a second transformer and a primary side of the second transformer, and is connected to a first side of the second transformer. A second control unit for controlling a current supply state to a secondary coil; and a second control unit connected to a secondary side of the second transformer. A second rectifier circuit for rectifying the electromotive force induced on the secondary side of the second transformer to generate a second output voltage; and winding concentrically with a primary coil of the second transformer. And an auxiliary winding for generating a power supply voltage of the first and second control units after activation. A phototransistor of the photocoupler is connected to the first control unit, and a photodiode of the photocoupler is provided. Is connected to an output of the first rectifier circuit, an output terminal of a second output voltage of the second rectifier circuit,
A resistor and a diode are connected in series between the high-potential terminal of the photodiode, and a low-potential terminal of the photodiode and a ground terminal of the second rectifier circuit. A power supply circuit, comprising: a switch circuit for controlling on / off of the first output voltage from a secondary side. 3. A power supply, comprising: a first voltage generator for generating a first output voltage; and a second voltage generator for generating a second output voltage, wherein the first voltage generator includes: A first transformer, a first controller connected to a primary side of the first transformer, and controlling a current supply state to a primary coil of the transformer; a secondary side of the first transformer A first rectifier circuit connected to the first transformer to rectify the electromotive force induced on the secondary side of the first transformer to generate a first output voltage; and A photocoupler that feeds back to a first control unit, wherein the second voltage generation unit is connected to a second transformer and a primary side of the second transformer, and is connected to a first side of the second transformer. A second control unit for controlling a current supply state to a secondary coil; and a second control unit connected to a secondary side of the second transformer. A second rectifier circuit for rectifying the electromotive force induced on the secondary side of the second transformer to generate a second output voltage; and winding concentrically with a primary coil of the second transformer. An auxiliary winding for generating a power supply voltage of the first and second control units after startup; a power supply voltage input terminal of the second control unit; and a power supply voltage input terminal of the first control unit. A switching circuit that is turned on when a potential of a power supply voltage input terminal of the second control unit rises above a predetermined potential, and a phototransistor of the photocoupler is provided between the first control unit and the first control unit; A photodiode of the photocoupler is connected to an output of the first rectifier circuit; an output terminal of a second output voltage of the second rectifier circuit;
A resistor and a diode are connected in series between the high-potential terminal of the photodiode, and a low-potential terminal of the photodiode and a ground terminal of the second rectifier circuit. A power supply circuit, comprising: a switch circuit for controlling on / off of the first output voltage from a secondary side.