JP2001161063A - Variable output voltage power supply - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To stabilize output voltage and balance current in a variable output voltage power supply device capable of changing output voltage. SOLUTION: When a switching transistor Q1 is turned on,
A pulse width control circuit 1 for controlling turning-off, and an output voltage Vou
The voltage detector 2 for detecting t, the current detector 3 for detecting current, and the difference between the current detected by the current detector 3 and the current detected by another power supply from the current balance terminal CB are output. An operational amplifier 5, which superimposes an output signal of the operational amplifier 5 on a reference value via a first diode D 1, compares the superposed signal with a voltage detection value of a voltage detector 3, and inputs the signal to a pulse width control circuit 1. And a reference voltage circuit including a series regulator SRG and the like, and a potential at a connection point of the first and second resistors R4 and R5 connected to the output terminal of the operational amplifier 5 is clamped to a part of the potential of the reference voltage circuit. And a second diode D2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output voltage variable power supply device for controlling an output voltage so as to stabilize an output voltage by switching control and to balance current during parallel operation.

[0002]

2. Description of the Related Art FIG. 2 is an explanatory view of a conventional example, in which T1 is a transformer, Q1 is a switching transistor, 1 is a pulse width control circuit (PWM), 2 is a voltage detector, 3 is a current detector, 4 to 7 Is an operational amplifier, D1, D11 and D12 are diodes, C1 is a capacitor, L1 is a choke coil, C
T is a current transformer, R1 to R4, R8 to R12 are resistors, Vr1 and Vr2 are reference voltages, 10 is an output voltage variable power supply having the same configuration, CB is a current balance terminal, Vcc is a power supply voltage, and Vin is a DC input voltage. , Vout indicate a DC output voltage.

A switching transistor Q1 is connected to a primary winding of a transformer T1, and the switching transistor Q1 is turned on and off by a pulse width control circuit 1, and rectification including diodes D11 and D12, a choke coil L1, and a capacitor C1. The smoothing circuit rectifies and smoothes the induced voltage of the secondary winding of the transformer T1 and applies it to the load as the output voltage Vout. When the output voltage Vout is applied to the load by operating the other output voltage variable power supplies 10 in parallel, the current balance terminals CB are connected to each other.

A voltage detector 3 detects an output voltage Vout and inputs the output voltage Vout to an operational amplifier 4, and outputs a reference voltage Vr1 to a resistor R
An output signal corresponding to the difference is input to the pulse width control circuit 1. The pulse width control circuit 1 controls the ON period of the switching transistor Q1 so that the difference becomes zero, thereby stabilizing the output voltage Vout. Also, by adjusting the reference voltage Vr1, the output voltage Vout can be set to a desired value.

The operational amplifier 6 compares the output voltage Vout with the reference voltage Vr2, and outputs an overvoltage alarm signal OVA when the output voltage Vout exceeds the reference voltage Vr2. The operational amplifier 7 compares the output voltage Vout with a value obtained by dividing the reference voltage Vr2 by the resistors R11 and R12, and outputs a voltage drop alarm signal UVA when the output voltage Vout falls below the divided value. For the overvoltage alarm signal OVA, for example, the pulse width control circuit 1
To control so that the ON period of the switching transistor Q1 is minimized.

Further, a current supplied to the load is detected by the current transformer CT and input to the current detection unit 2, and a current detection value from the current detection unit 2 is input to the operational amplifier 5. The current detection unit 2 has a configuration in which, for example, a current flowing through the secondary winding of the current transformer CT is converted into a voltage by a resistor, and the voltage is output as a DC detection value by peak rectification or the like. Also, a resistor R connected to the operational amplifier 5
Assuming that the current detection value from the current detection unit 2 and the current detection value from the current balance terminal CB of the other output voltage variable power supply device 10 are the same, if R 8 and R 9 have the same resistance value, the operational amplifier 5 The output signal becomes 0.

When the current detection value of the other output voltage variable power supply 10 is large, the output signal of the operational amplifier 5 has a positive value, and the resistance of the resistor R4 and the diode D1.
2 is applied to the connection point a of R3. As a result, the divided voltage at the connection point b between the resistors R1 and R2 of the operational amplifier 4 increases, and the pulse width control circuit 1 lengthens the ON period of the switching transistor Q1 in the direction to increase the output voltage Vout. Thus, since the load current can be increased, the current balance with another output voltage variable power supply device 10 can be balanced.

[0008]

In the above-described conventional example, the output signal of the operational amplifier 5 changes in the range of 0 to Vcc in accordance with the difference between the input current detection values. As a result, the potential of the connection point a of the resistors R2 and R3 also changes correspondingly, and the potential of the connection point b of the resistors R1 and R2 as the reference voltage for the operational amplifier 4 is increased, so that the pulse width control circuit 1 In some cases, the on-period of the switching transistor Q1 is made unnecessarily long, and the output voltage Vout is increased, resulting in an overvoltage state. That is, there is a problem in stability during the parallel operation.

SUMMARY OF THE INVENTION It is an object of the present invention to stabilize an output voltage and balance current by controlling a reference voltage to be compared with an output voltage not to rise more than necessary in an output voltage variable power supply device. .

[0010]

The variable output voltage power supply of the present invention comprises: (1) a voltage detector 3 for detecting an output voltage;
An operational amplifier 4 for controlling an output voltage for comparing a voltage detected by the voltage detector 2 with a reference value;
And a pulse width control circuit 1 that performs switching control in accordance with the output signal of
A switching transistor Q1 that is turned on and off by the pulse width control circuit 1, a rectifying / smoothing circuit connected to the secondary winding of the transformer T1, and a current detection unit 2 that detects a current flowing through the secondary winding of the transformer T1. , This current detection unit 2
And a current-balanced operational amplifier 5 that compares the current detection value of the other output voltage with the current detection value of another output voltage variable power supply and superimposes the comparison output signal on the reference value of the operational amplifier 4. A reference voltage circuit for setting a reference value of the operational amplifier 4 for output voltage control and an output signal of the operational amplifier 5 for current balance are superimposed on the reference value of the operational amplifier 4 for output voltage control. The first resistor R4 and the second diode R1 connected to the first resistor R4 and the first diode D1, the predetermined potential point of the reference voltage circuit, and the output terminal of the operational amplifier 5 for current balance. And a second diode D2 connected so as to clamp the potential of the connection point.

(2) The reference voltage circuit applies a series circuit using the potential at the connection point between the resistor R6 and the series regulator SRG as a reference voltage, a variable resistor VR controlling the series regulator SRG, and a reference voltage. A plurality of resistors R1,
A series circuit of R2 and R3 and a resistance voltage dividing point b of this series circuit
Is used as the reference value of the operational amplifier 4 for controlling the output voltage, and the output signal of the operational amplifier 5 for balancing the current is supplied to the first and second resistors R4 and R5 and the first diode D at another resistance voltage dividing point a.
1 and a circuit for applying the voltage via the control circuit 1.

(3) An operational amplifier 6 for outputting a reference voltage of a reference voltage circuit to output an overvoltage alarm signal OVA when the output voltage rises, and an operational amplifier 7 for outputting a voltage drop alarm signal UVA when the output voltage drops. And a reference voltage.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an embodiment of the present invention, wherein T1 is a transformer, Q1 is a switching transistor, 1 is a pulse width control circuit (PWM), 2 is a voltage detector, and 3 is a current detector. The detecting sections 4 to 7 are operational amplifiers. The operational amplifier 4 is for output voltage control, the operational amplifier 5 is for current balance, the operational amplifier 6 is for an overvoltage alarm, and the operational amplifier 7 is for a voltage drop alarm. D1, D2, D1
1, D12 is a diode, C1 is a capacitor, L1 is a choke coil, CT is a current transformer, R1 to R12.
Is a resistor, VR is a variable resistor, SRG is a series regulator, CB is a current balance terminal, V and Vcc are power supply voltages,
Vin indicates a DC input voltage, and Vout indicates a DC output voltage.

This embodiment employs resistors R1 to R3, R
6, R7, variable resistor VR, and series regulator S
A reference voltage circuit is formed by RG, and a stabilized potential at a connection point c between the resistors R6 and R7 is set as a reference voltage. This reference voltage is controlled by a series regulator S using a variable resistor VR.
It can be set arbitrarily by controlling the RG. This reference voltage is applied to a series circuit of the resistors R1 to R3, and a connection point b between the resistors R1 and R2 is set as a reference value to be input to the operational amplifier 4. Further, a reference voltage is applied to the resistors R11 and R12, and is used as a reference value for the operational amplifier 6 for an overvoltage alarm and the operational amplifier 7 for a voltage drop alarm.

The first and second resistors R4 and R5 and the first diode D are connected to the output terminals of the operational amplifier 5 for current balance.
1 and this first diode D1 is connected to a resistor R
2, R3, and a first and second resistor R4,
The second diode D2 is connected between the connection point of R5 and the connection point c of the resistors R6 and R7. The second diode D2 is connected so that the potential at the connection point between the first and second resistors R4 and R5 can be clamped to the potential at the connection point c.

Accordingly, when a current detection value from another output voltage variable power supply is input to the current balance terminal CB, and this current detection value is larger than the current detection value from the current detection unit 2, the current balance The output signal of the operational amplifier 5 becomes large, for example, when it becomes the power supply voltage Vcc or a value close thereto, a forward voltage is applied to the second diode D2. Resistance R
The potential at the connection point between the terminals 4 and R5 is clamped to the potential at the connection point c. As a result, a rise in the potential of the connection point a is suppressed, and accordingly, a rise in the potential of the connection point b, that is, a reference value of the operational amplifier 4 for controlling the output voltage is suppressed. Can be avoided.

The reference voltage circuit can arbitrarily set a reference voltage using a variable resistor VR. By setting this reference voltage as the reference voltage of the operational amplifiers 6 and 7, the output voltage V
Since the detection reference value of the overvoltage alarm and the detection reference value of the voltage drop alarm are automatically changed with the change of the setting of out, the configuration of the reference voltage source is simplified, and the setting of the output voltage Vout can be easily changed. There are advantages.

The present invention is not limited to the above-described embodiment, but can be variously added and changed. For example, the above-described embodiment shows a forward converter type, but a flyback converter type. And other types of converters. The reference power supply circuit is a series regulator SRG
Is shown, but it is also possible to use a circuit having another voltage stabilizing means such as a Zener diode.
It is also possible to provide a configuration for performing overcurrent protection using the current detection value of the current detection unit 2.

[0019]

As described above, the present invention relates to a series regulator S for setting a reference value of an operational amplifier 4 for controlling an output voltage in a power supply device for switching control.
A first resistor R4 connected to a reference voltage circuit including RG and the like and an output signal of the operational amplifier 5 for current balance superimposed on a reference value of the operational amplifier 4 for output voltage control;
, A point of a predetermined potential of the reference voltage circuit (connection point c), and a connection point between the first resistor R4 and the second resistor R5 connected to the output terminal of the operational amplifier 5 for current balance. And a second diode D2 connected so as to clamp the potential at this connection point. When the difference between the current detection values during parallel operation is large, the output signal of the operational amplifier 5 for current balance is provided. Can be increased to near the power supply voltage Vcc, and by clamping the potential at the connection point of the resistors R4 and R5 via the second diode D2, it is possible to avoid an extreme increase in the output voltage Vout, There is an advantage that the operation can be stabilized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 pulse width control circuit (PWM) 2 current detector 3 voltage detector 4 operational amplifier for output voltage control 5 operational amplifier for current balance 6 operational amplifier for overvoltage alarm 7 operational amplifier for low voltage alarm T1 transformer Q1 switching Transistor SRG Series regulator R1, R2 First and second resistors D1, D2 First and second diodes CB Current balance terminal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazutoshi Fuchigami 1-17-3 Sakado, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Inside Fuji Denso Co., Ltd. (72) Inventor Hiroshi Shimamori 4-chome, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture No. 1 No. 1 Fujitsu Limited F term (reference) 5H730 AA20 BB23 DD02 EE08 EE59 FD01 FD31 FG05 FV07 XX03 XX12 XX13 XX23 XX32 XX33 XX50

Claims (3)

[Claims] 1. A voltage detecting section for detecting an output voltage, an operational amplifier for controlling an output voltage for comparing a voltage detected by the voltage detecting section with a reference value, and switching corresponding to an output signal of the operational amplifier. A pulse width control circuit that performs control, a switching transistor that is connected to the primary winding of the transformer and that is turned on and off by the pulse width control circuit,
A rectifying / smoothing circuit connected to the secondary winding of the transformer, a current detection unit for detecting a current flowing in the secondary winding of the transformer, and a current detection value obtained by the current detection unit and another output voltage variable power supply device. A current-balanced operational amplifier for comparing a detected current value and superimposing a comparison output signal on the reference value of the operational amplifier. A reference voltage circuit for setting a reference value; a first resistor and a first diode connected to superimpose an output signal of the operational amplifier for current balance on the reference value of the operational amplifier for output voltage control A potential of the connection point between a point of a predetermined potential of the reference voltage circuit and a connection point of the first and second resistors connected to an output terminal of the operational amplifier for current balancing. Clamp Variable output voltage power supply apparatus characterized by comprising a second diode connected to. 2. A reference voltage circuit, comprising: a series circuit using a potential at a connection point between a resistor and a series regulator as a reference voltage; a variable resistor controlling the series regulator;
A series circuit of a plurality of resistors for applying the reference voltage, and a resistance voltage dividing point of the series circuit is used as a reference value of the operational amplifier for controlling the output voltage. 2. The output voltage variable power supply device according to claim 1, further comprising a circuit for applying an output signal of the amplifier via first and second resistors and a first diode. 3. An operational amplifier that outputs an overvoltage alarm signal when the output voltage rises, and an operational amplifier that outputs a voltage drop alarm signal when the output voltage drops. 3. The output voltage variable power supply device according to claim 1, wherein the output voltage variable power supply device has a voltage configuration.