JPH07319564A - Power source circuit - Google Patents

Abstract

PURPOSE:To provide a power source circuit capable of reducing a driving voltage on the light emitting part of a photocoupler used in the feedback circuit of a control signal and sufficiently performing a voltage stabilizing operation for a voltage control circuit even when the current transmission rate of the photocoupler is decreased due to the secular change, etc. CONSTITUTION:The voltage stabilizing operation for an input voltage Vi is performed by the voltage control circuit 5, the potential dividing resistors 10, 11 for an output voltage Vo, a reference voltage source 9, an error amplifier circuit 8, the photocoupler 6, and a resistor 12. The light emitting part 6b of the photocoupler 6 generates a current Id and light corresponding to an error voltage Ve outputted from the error amplifier circuit 8 and the resistance value R12 of the resistor 12, and the light receiving part 6b of the photocoupler 6 controls the control circuit 5 by the control signal Ic corresponding to the light. A current bypassing the resistor 12 can be supplied from the output terminal of the error amplifier circuit 8 to the light emitting part 6b in a range in which the error voltage Ve is changed from the voltage Vb to the maximum value Va by a transistor 13, resistors 14, 16 and a Zener diode 15.

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 for converting a DC input voltage into a DC output voltage whose voltage is stabilized by the control of a control circuit, and more particularly to a power supply circuit using a photocoupler as a feedback circuit for a control signal to the control circuit. Regarding

[0002]

2. Description of the Related Art In a conventional power supply circuit of this type, a DC input voltage Vi applied to an input terminal is converted into a voltage by a control circuit such as a switching circuit to obtain a voltage-stabilized DC output voltage Vo at an output terminal. ing. This power supply circuit needs to feed back a control signal corresponding to the DC output voltage Vo to the control circuit so that the DC output voltage Vo becomes a predetermined voltage Vs. It uses a coupler. That is, the photocoupler includes the built-in light emitting unit via the protection resistor for the error voltage Ve as a result of comparing the DC output voltage Vo (or the detection voltage Vd of the voltage Vo) with the reference voltage Vr serving as the reference of the predetermined voltage Vs. A current Id is applied to the current input end of the light emitting element to apply a light having an intensity corresponding to the current Id flowing through the light emitting portion to the built-in light receiving portion.
Then, this light receiving portion receives a current I corresponding to the intensity of the received light.
c or the conduction resistance Rt as a control signal of the control circuit,
The control circuit is feedback-controlled by this control signal to perform DC voltage conversion. As the power supply circuit using the photocoupler for the feedback circuit of the control signal as described above, Japanese Patent Laid-Open Publication No. 3-265462 (switching power supply), Hei 2-201614 (error amplifier of stabilized power supply device)
Flat 1-291662 (switching power supply), Sho 62-
Techniques such as No. 100818 (voltage detection switch circuit) and Japanese Utility Model Publication No. 62-185490 (output voltage detection circuit of insulation type converter) are disclosed.

In the photo coupler, the light emitting portion is generally composed of a photodiode and the light receiving portion is composed of a phototransistor. In such a photo coupler,
The phototransistor receives the light emitted from the photodiode that supplies the current Id. The phototransistor produces a current Ic corresponding to the intensity of the received light. Conduction resistance Rt between the collector terminal and the emitter terminal of the phototransistor
Is high when the light intensity received by the phototransistor is low, and is low when the light intensity is high.

There is a relation of the formula (1) between the currents Id and Ic.

Ic = Ctr × Id (1) where Id is the diode current flowing in the photodiode, Ic is the control current flowing from the collector terminal to the emitter terminal of the phototransistor, and Ctr is the current transfer rate. This is a constant of the photocoupler that represents the efficiency of current transmission from the light receiving unit to the light receiving unit. The conduction resistance Rt of the phototransistor is in inverse proportion to the control current Ic, and is determined if the control current Ic is given.

The diode current Id is determined by the error voltage Ve and the resistance value R of the protective resistor, and is represented by the relationship of the equation (2).

Id = Ve / R (2)

In the conventional power supply circuit described above, the current Id flowing through the light emitting portion of the photocoupler is controlled by the error voltage Ve driving the light emitting portion and the protective resistor connected to the light emitting portion. Therefore, the upper limit of the control signal (the upper limit of the control current Ic or the lower limit of the conduction resistance Rt) supplied from the light receiving portion of the photocoupler to the control circuit and the magnitude of the DC voltage which the control circuit can control are limited. There was a problem.

Further, the current transfer rate C of the photocoupler is
tr tends to become smaller due to aging, but due to the decrease in the current transfer rate Ctr, a control signal (current Ic or conduction resistance) of a magnitude necessary for the control circuit to control the DC output voltage Vo at a constant voltage. In some cases, Rt) could not be supplied.

Therefore, the present invention is to solve the above-mentioned problems of the power supply circuit according to the prior art, is not limited to the drive voltage Ve of the photocoupler, and the current transfer rate Ctr of the photocoupler is small. It is an object of the present invention to provide a power supply circuit that can supply a control signal of a sufficient magnitude to a control circuit even if the power supply voltage drops.

[0010]

One of the power supply circuits of the present invention is a control circuit for converting a DC input voltage supplied to an input terminal into a DC output voltage at an output terminal by controlling a control signal, and An output voltage detection circuit that detects a DC output voltage, a reference voltage generation circuit that generates a reference voltage, and an error amplification that amplifies a difference voltage between the detected DC output voltage and the reference voltage to generate an error voltage at an output end. A circuit, a photocoupler for receiving the error voltage at the input end of the light emitting unit through the first resistor and generating the control signal from the light receiving unit, and a current input terminal connected to the output end of the error amplification circuit. A three-terminal amplifying element having a current output terminal connected to the current input terminal of the light emitting portion of the photocoupler, and a Zener die for applying a predetermined bias voltage to the current control terminal of the three-terminal amplifying element And an over-de.

One of the power supply circuits is configured such that the three-terminal amplifying element is a bipolar transistor having the current input terminal as an emitter terminal, the current output terminal as a collector terminal, and the current control terminal as a base terminal. be able to.

Another one of the power supply circuits is a field-effect transistor in which the three-terminal amplifying element has a source terminal for the current input terminal, a drain terminal for the current output terminal, and a gate terminal for the current control terminal. Can have a configuration that is

Further, another one of the power supply circuits is
The error amplification circuit may be an operational amplifier that uses the DC output voltage generated at the output terminal of the control circuit as a power supply voltage.

Another aspect of the power supply circuit of the present invention is a control circuit for converting a DC input voltage supplied to an input terminal into a DC output voltage at an output terminal by controlling a control signal, and the DC output. An output voltage detection circuit for detecting a voltage, a reference voltage generation circuit for generating a reference voltage, and an error amplification circuit for amplifying a difference voltage between the detected DC output voltage and the reference voltage to generate an error voltage at an output end. In a power supply circuit including a photocoupler that receives the error voltage at an input end of a light emitting unit via a first resistor and generates the control signal from a light receiving unit, a predetermined voltage lower than a maximum value of the error voltage In the range of the maximum value of the error voltage, a bypass circuit for bypassing the first resistor and supplying a current to the light receiving portion of the photocoupler is further provided.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

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

This power supply circuit has a positive voltage power input terminal 1
The DC input voltage Vi is applied between the ground terminal 2 and the ground terminal 2.
The DC input voltage Vi is converted into a DC output voltage Vo whose voltage is stabilized by the control circuit 5 controlled by the control current Ic, and this DC output voltage Vo is output between the output terminal 3 of positive voltage power and the ground terminal 4. Is output to. Here, the control circuit 5 uses the control current Ic or the conduction resistance Rt (both are collectively referred to as a control signal) generated by the phototransistor 6a, which is the light receiving portion of the photocoupler 6, in the same manner as disclosed in the above publication. It is a voltage conversion circuit that changes Vo, and specifically, it includes a pulse conduction period control circuit of a switching power supply, a series regulator type voltage drop amount control circuit, and the like.

The DC output voltage Vo is divided by resistors 10 and 11 connected in series between the output terminal 3 and the ground terminal 4, and the DC output voltage Vo is applied to the connection point between the resistors 10 and 11.
A detection voltage Vd which is the detection result of is generated. Further, the reference voltage source 9 generates a reference voltage Vr which is a reference of a predetermined voltage Vs which is a desired DC output voltage of the power supply circuit. The detection voltage Vd is applied to the plus (+) input terminal of the error amplification circuit 8, and the reference voltage Vr is applied to the minus (−) input terminal of the error amplification circuit 8. The error amplification circuit 8 is a differential amplifier that uses the DC output voltage Vo as a power supply voltage and is configured by an operational amplifier or the like. The error amplification circuit 8 has voltages Vd and V
The difference with r is taken, and this difference voltage (Vd−Vr) is further amplified with an amplification degree determined by an internal constant to generate a positive potential error voltage Ve. This error voltage Ve is applied to the current input terminal of the photodiode 6b, which is the light emitting portion of the photocoupler 6, via the resistor 12 having the resistance value R12, and the photodiode 6b generates the diode current Id between itself and the ground terminal. Shed. The photodiode 6b produces light having an intensity corresponding to the diode current Id.

The photo coupler 6 is a photodiode 6b.
The phototransistor 6a, which is the light receiving portion, receives the light radiated by. The phototransistor 6a produces a control current Ic corresponding to the intensity of the received light. Phototransistor 6a
Resistance Rt between the collector terminal and the emitter terminal of the
Is high when the light intensity received by the phototransistor 6a is low, and is low when the light intensity is high.

The collector terminal and the emitter terminal of the phototransistor 6a are respectively connected to different control signal input terminals of the control circuit 5, and the control circuit 5 controls the DC output voltage Vo by using the control current Ic or the conduction resistance Rt as a control signal. I do. In this embodiment, the control circuit 5 works to increase the DC output voltage Vo when the conduction resistance Rt is high, and conversely, when the conduction resistance Rt is low, the control circuit 5 increases the DC output voltage Vo.
Works to lower.

The power supply circuit of this embodiment further comprises the following components in addition to the above-mentioned basic circuit which uses the photocoupler 6 as the feedback circuit of the control signal to the control circuit 5.

In the bipolar transistor 13 which is one of the three-terminal amplifying elements, the emitter terminal which is a current input terminal is the output terminal of the error amplifier circuit 8 and the collector terminal which is a current output terminal is the current input of the photodiode 6b. Connected to each end. Further, a series circuit of the resistor 14 and the Zener diode 15 is connected between the output end of the error amplification circuit 8 and the ground potential. The Zener diode 15 receives the error voltage Ve via the resistor 14 and generates a substantially constant Zener voltage Vz between the cathode terminal and the anode terminal (ground potential). Zener diode 1
The cathode terminal of 5 and the base terminal, which is the current control terminal of the transistor 13, are connected via a resistor 16 that limits the inflow of an excessive current into the base terminal. The Zener diode 15 applies a bias voltage Vz1 substantially equal to the Zener voltage Vz to the base terminal of the transistor 13. In these components, the magnitude of the control signal supplied to the control circuit 5 is rarely limited to the error voltage Ve, which is the drive voltage of the photodiode 6b, and the resistance value R12 of the resistor 12, and moreover, the photocoupler 6 is used. Current transfer rate C
This is provided in order to supply a control signal of sufficient magnitude to the control circuit 5 even if tr drops below the initial value due to changes with time or the like.

First, the basic operation of this embodiment will be described.
At the time when the DC input voltage Vi is first applied between the input terminal 1 and the ground terminal 2, the DC output voltage Vo does not appear between the output terminal 3 and the ground terminal 4, and this voltage Vo is a resistor. The detection voltage Vd divided by 10 and 11 is 0V. The detection voltage Vd and the reference voltage Vr from the reference voltage source 9 are input to the error amplification circuit 8. Error amplifier circuit 8
Causes an error voltage Ve corresponding to the difference voltage between the detection voltage Vd and the reference voltage Vr in the normal operation.
Since the power source is obtained from between the output terminal 3 and the ground terminal 4, the error voltage Ve output in this case is 0V.
In this state, the photodiode 6 of the photo coupler 6
Since the diode current Id does not flow in b and the photodiode 6a receives no light, the conduction resistance Rt is high. Therefore, in the initial application state of the DC input voltage Vi, the control circuit 5 is controlled by the high conduction resistance Rt and operates to increase the DC output voltage Vo.

When the detection voltage Vd rises and exceeds the reference voltage Vr as time elapses after the DC input voltage Vi is applied to this power supply circuit and the DC output voltage Vo rises, the error amplifying circuit 8 operates. The output error voltage Ve increases. Then, this error voltage Vo is applied to the current input terminal of the photocoupler 6 via the resistor 12, and the diode current Id flows through the photodiode 6b. As a result, the conduction resistance Rt of the phototransistor 6a decreases, and the control circuit 5 acts to decrease the DC output voltage Vo.

After all, the power supply circuit of the present embodiment is controlled by the above-described basic operation so that the detection voltage Vd becomes equal to the reference voltage Vr, and the DC output voltage Vo is also the target predetermined voltage Vr.
It will be controlled to a constant value equal to s.

Here, the error voltage V in this power supply circuit
The maximum value Va of e is limited to a DC output voltage Vo-1.5V when a μPC125IC (manufactured by NEC Corporation), which is one of operational amplifiers, is used for the error amplification circuit 8. Also, the threshold voltage Vt of the photodiode 6a is
When a PS2501 photocoupler (manufactured by NEC Corporation) is used as the photocoupler 6, the voltage is about 1.2V. Therefore, the diode current Id is limited by the equation (3) when the above circuit element is used.

Id <(Vo-Va-Vt) /R12.apprxeq. (Vo-1.5-1.2) / R12 (3) The power source of the error amplifier circuit 8 is the output terminal 3 and the ground terminal 4.
And the power supply voltage Vo of the error amplifier 8
Although it is possible to relax the upper limit of the diode current Id by increasing, the disadvantage is that the power supply circuit becomes complicated.

FIG. 2 is a diagram showing the relationship between the error voltage Ve and the diode current Id in this embodiment. The characteristic operation of this embodiment will be described below with reference to FIGS.

This power supply circuit operates within the operating range of the above-mentioned basic constant voltage control operation from the error voltage Ve of 0V to the error voltage Ve.
To a basic value Vb that is lower than the maximum value Va. Now, assuming that the current transfer efficiency Ctr of the photocoupler 6 is lowered due to aging, the error amplification circuit 8
The error voltage Ve is increased to allow more photodiode current Id to flow through the photodiode 6b, the conduction resistance Rt of the phototransistor 6a is maintained at a predetermined value, and the control circuit 5 can maintain the DC output voltage Vo at the predetermined voltage Vs. To do so. Curve B in FIG. 2 illustrates the above description.

Originally, this power supply circuit can raise the diode current Id as shown by the broken line curve C with the rise of the error voltage Ve to reach the point of the maximum value Va. However, this power supply circuit includes a transistor 13,
Resistors 12 and 14, and Zener diode 15
Is added, the diode current Id can be increased more than in the basic constant voltage control in the error voltage Ve range from the basic value Vb to the maximum value Va.

The basic value Vb is set equal to the sum of the Zener voltage Vz of the Zener diode 15 and the emitter-base voltage V _BE (about 0.7 V) of the transistor 13. When the error voltage Ve rises above the basic value Vb, a current flows from the base terminal of the transistor 13 to the Zener diode 15 via the resistor 16. As a result, the collector / emitter of the transistor 13 becomes conductive, and the resistor 12
The current flowing into the photodiode 6a from the emitter terminal (collector terminal) of the transistor 13 by bypassing is also added as the diode current Id. Curve A in FIG. 2 illustrates the above description. As described above, in this power supply circuit, in the error voltage Ve range from the basic value Vb to the maximum value Va, the rate of change of the diode current Id with respect to the change of the error voltage Ve is increased. Therefore, this power supply circuit relaxes the limit of the error voltage Ve accompanying the limit of the power supply voltage Vo of the error amplification circuit 8 and the maximum limit of the diode current Id due to the existence of the resistance value R12 of the resistor 12, and eventually The upper limit of the control signal supplied to the control circuit 5 is relaxed to make the constant voltage control of this power supply circuit more reliable. Thus, the error voltage Ve
Increasing the rate of change of the diode current Id with respect to the change of is particularly effective when the error amplifier circuit 8 cannot obtain a high-voltage power supply.

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

This power supply circuit is a three-terminal amplifying element,
A field effect transistor (FET) 17 is used instead of the transistor 13 in FIG. FET17 is
The current input terminal of the three-terminal amplifier corresponds to the source terminal, the current output terminal corresponds to the drain terminal, and the current control terminal corresponds to the gate terminal. The source terminal of the FET 17 is connected to the output terminal of the error amplifier circuit 8, the gate terminal is connected to the cathode terminal of the Zener diode 15, and the drain terminal is connected to the current input terminal of the photodiode 6b. Moreover, the resistor 16 can be omitted in this power supply circuit. The other circuits are the same as the power supply circuit of the embodiment shown in FIG.

In this power supply circuit, the reference value Vb is the Zener voltage Vz generated by the Zener diode 15 and the FET 17
Is set to be equal to the sum of the threshold voltage Vgt of the gate. When the error voltage Ve rises above the reference value Vb, the drain / source of the FET 17 becomes conductive, the current that bypasses the resistor 12 and flows into the photodiode 6a from the source terminal (drain terminal) of the FET 17 is also added as the diode current Id. . Therefore, the operation of this power supply circuit has the same relationship as that shown in FIG.

[0035]

As described above, according to the present invention, the current input terminal of the three-terminal amplifying element is connected to the output terminal of the error amplifying circuit, and the current output terminal is connected to the current input terminal of the light emitting portion of the photocoupler. Since a predetermined bias voltage is applied to the current control terminal by the Zener diode, a control signal for controlling the control circuit for DC voltage conversion can be supplied from the light receiving portion of the photocoupler with less restriction of the drive voltage from the error amplification circuit, This has the effect of improving the stability of the DC output voltage.

Further, according to the present invention, with the above structure, a control signal of a sufficient magnitude can be supplied to the control circuit even if the current transfer rate Ctr of the photocoupler is lowered, and the DC output voltage can be stabilized in the same manner as described above. There is an effect that can improve the degree.

[Brief description of 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 diagram showing a relationship between an error voltage Ve and a diode current Id in this embodiment.

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

[Explanation of symbols]

 1 Input Terminal 2, 4 Ground Terminal 3 Output Terminal 5 Control Circuit 6 Photocoupler 6a Phototransistor 6b Photodiode 8 Error Amplifier 9 Reference Voltage Source 10-12, 14, 16 Resistor 13 Transistor 15 Zener Diode 17 Field Effect Transistor (FET) )

Claims (5)

[Claims] 1. A control circuit for converting a direct-current input voltage supplied to an input terminal into a direct-current output voltage at an output terminal by converting the direct-current voltage by controlling a control signal, an output-voltage detection circuit for detecting the direct-current output voltage, and a reference voltage. Through a first resistor, an error amplifier circuit that amplifies the difference voltage between the detected DC output voltage and the reference voltage to generate an error voltage at the output end, and the error voltage through a first resistor. A photocoupler for receiving the control signal from the light receiving section and receiving the control signal from the light receiving section, and connecting the current input terminal to the output terminal of the error amplification circuit and the current output terminal to the current input terminal of the light emitting section of the photocoupler A power supply circuit comprising: a three-terminal amplifying element connected to the above; and a Zener diode that applies a predetermined bias voltage to a current control terminal of the three-terminal amplifying element. 2. The three-terminal amplifying element, wherein the current input terminal is an emitter terminal, the current output terminal is a collector terminal,
The power supply circuit according to claim 1, wherein the current control terminal is a bipolar transistor having a base terminal. 3. The three-terminal amplifying element is a field effect transistor in which the current input terminal is a source terminal, the current output terminal is a drain terminal, and the current control terminal is a gate terminal. The power supply circuit described. 4. The power supply circuit according to claim 1, wherein the error amplification circuit is an operational amplifier which uses the DC output voltage generated at the output end of the control circuit as a power supply voltage. 5. A control circuit for converting a DC input voltage supplied to an input terminal into a DC output voltage at an output terminal by converting the voltage by controlling a control signal, an output voltage detection circuit for detecting the DC output voltage, and a reference voltage. Through a first resistor, an error amplifier circuit that amplifies the difference voltage between the detected DC output voltage and the reference voltage to generate an error voltage at the output end, and the error voltage through a first resistor. In a power supply circuit including a photocoupler for receiving the control signal from the light receiving portion while receiving the control signal from the light receiving portion at the input terminal, The power supply circuit further comprising a bypass circuit that bypasses the resistor 1 and supplies a current to the light receiving portion of the photocoupler.