JPH0222724Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a series control power supply device that prevents output voltage overshoot when power is disconnected and protects a load.

FIG. 1 is a circuit diagram showing an example of a conventional device of this type.
The negative electrode of the power source 1 is connected to the negative output terminal 4. In addition, the second circuit outputs the reference voltage Vref.
Connect the negative pole of the power supply 5 to the positive output terminal 3,
The positive terminal of the power supply 5 is connected to the negative output terminal 4 via voltage dividing resistors 6 and 7 in series, and this divided voltage is applied to the non-inverting input of a differential amplifier 8. Further, the inverting input of this differential amplifier 8 is connected to the positive output terminal 3, and the output is applied to the base of the transistor 2 via the resistor 9 to control the output voltage V ₀ between the output terminals 3 and 4 to a predetermined voltage. I have to. Further, reference numerals 10 and 11 are third and fourth power supplies having positive and negative poles for driving the differential amplifier 8, and have their negative and positive poles connected to the positive output terminal 3, respectively. The first to fourth power supplies 1, 5, 10, and 11 are obtained by, for example, lowering the voltage of a commercial power source using a circuit not shown, rectifying it, and smoothing it.

However, with something like this, output terminals 3 and 4
Loads such as semiconductor circuits with strict operating voltage tolerance 1
If 2 is connected, if the output voltage overshoots when the power supply is disconnected, there is a risk that the load will fail or be damaged. Such an overshoot in the output voltage occurs especially when the power supply is disconnected, due to irregularities in the rising and falling edges of the first, third, and fourth power supplies 1, 10, and 11. This occurs when the series control transistor 2 is biased in the conduction direction when the voltage rises or when a charge remains in the smoothing capacitor. Specifically, in the circuit diagram shown in FIG. 1, the third power supply 10, which is a positive power supply, starts up earlier when the power is turned on than the fourth power supply 11, which is a negative power supply for the operational amplifier 8, or the power supply is delayed. If the voltage falls late during the disconnection, the output of the differential amplifier 8 swings to the positive polarity side. When voltage is being output from the first power supply 1, an overvoltage occurs due to overshoot.

The present invention has been developed in view of the above circumstances, and an object of the present invention is to provide a series control power supply device that has a simple configuration and can reliably prevent overshoot when the power supply is disconnected.

Hereinafter, one embodiment of the present invention will be described in detail with reference to a circuit diagram shown in FIG. 2, in which the same parts as in FIG. 1 are given the same reference numerals. In the figure, 13 is a switching transistor whose collector and emitter are connected between the base and emitter of the series control transistor 2, and a resistor 14 is connected to this base in series between the third and fourth positive and negative power supplies 10 and 11. A divided voltage of 15 is given. The bias voltage divided by the resistors 14 and 15 and applied to the base of the switching transistor 13 cuts off the transistor 13 if the output voltages of the third and fourth power supplies 10 and 11 are at normal values. Further, when the positive output of the third power supply 10 rises earlier or falls later than the negative output of the fourth power supply 11, the output of the differential amplifier 8 swings toward the positive polarity side in an uncontrolled state. In this case, the positive output of the differential amplifier 8 attempts to make the series control transistor 2 conductive, but the switching transistor 13 to which the divided voltages of the third and fourth power supplies 10 and 11 are supplied is rendered conductive. death,
A bias is applied to the base of the series control transistor 2 to cut off the transistor 2.
Therefore, the first power supply 1 is cut off by the series control transistor 2, and the power supply to the load 12 can be stopped. Therefore, it is possible to reliably prevent an overshoot of the output voltage when the power is turned on or off, thereby preventing overvoltage from being applied to the load. Further, when an uncontrolled bias voltage is applied to the series control transistor 2 in the conduction direction, the switching transistor 13 is used to conduct the series control transistor 2 by the bias voltage and cut off the series control transistor 2. Therefore, the overall configuration is extremely simple and the cost is low.

Note that the present invention is not limited to the above-mentioned embodiment, and for example, as the series control transistor 2.
A PNP type transistor may be used and inserted between the negative electrode of the first power supply 1 and the negative output terminal 4.

Further, in the above embodiment, a switching transistor 13 is inserted between the base of the series control transistor 2 and the positive output terminal 3, so that the series control transistor 2 is cut off when the switching transistor 13 is conductive. However, the switching transistor 13 is connected in series with the base of the control transistor 2 and the fourth power supply 1 of negative polarity.
1, or a Zener diode may be inserted in series with this switching transistor or in the base voltage dividing circuit.

As detailed above, in the present invention, a series control transistor is inserted between the power supply and the load, and the difference between the reference voltage and the output voltage is obtained by a differential amplifier, and the series control transistor performs constant voltage control. In the above device, when a bias in the conduction direction is applied to the series control transistor due to an unbalance of the driving voltage of the differential amplifier when the power supply is disconnected or disconnected, the transistor controlled by the divided voltage of the power supply is made conductive. A bias is applied to cut off the series control transistor. Therefore, it is possible to provide a series control power supply device that can reliably prevent output voltage overshoot when the power is disconnected with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional power supply device,
FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1, 5, 10, 11...power supply, 2...series control transistor, 3, 4...output terminal, 8...differential amplifier, 12...load, 13...switching transistor.

Claims (1)

[Scope of utility model registration request] In a series control power supply device, when the voltage of the two positive and negative power supplies that drive the differential amplifier that obtains the error of the output voltage with respect to the reference voltage deviates from the normal value and outputs a voltage that makes the series control transistor conductive, the above positive - A series control power supply device characterized in that a semiconductor switch operated by a divided voltage of a voltage divider circuit connected between two negative power supplies is made conductive, and a voltage is applied to the base of a control transistor to cut off the transistor.