JPS63236111A - Breaking circuit for power unit - Google Patents

Abstract

PURPOSE:To avoid the generation of heat of a power supply by connecting a 3rd transistor which is started by a charging current of a capacitor and cut off with drop of the output voltage between the 1st and 2nd transistors. CONSTITUTION:In an overcurrent state a transistor (TR) 4 is driven by the voltage drop of an overcurrent detecting resistance 2 and a TR 5 on a line is insufficiently driven to cause the drop of the output voltage. When the output voltage drops lower than the voltage level of a constant voltage diode 18, a TR 16 is not driven any more and cut off. Accordingly, the TR 5 is also cut off so that the generation of heat can be avoided in an abnormal state (overcurrent, short circuit, etc.). The similar actions and voltage drop to those said above are produced also in case where a control circuit 8 drives a TR 7 at a starting time point by an ON/OFF signal (signal input terminal 11).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a cutoff circuit for a power supply device that detects a drop in output voltage and cuts off input and output.

In conventional technology power supply networks, when the output experiences an overcurrent or short circuit,
The load on the input side and power supply circuit increases.

FIG. 2 shows a typical power supply circuit that controls output. An output terminal 12 controlled by a transistor 5 (first transistor) is provided for the input power source 1. The transistor 5 is controlled through the transistor 7 (second transistor) and the limiting resistor 6 by a control circuit 8 which turns the output on and off in response to a certain signal from a terminal 11 and controls the output to a desired constant voltage. Furthermore, when an overcurrent flows through the overcurrent detection resistor 2, the overcurrent protection transistor 4 is driven and the bias of the transistor 5 is lowered to suppress the overcurrent.

Problems to be Solved by the Invention However, such conventional power supply circuits result in large power loss when the output is overcurrent or short-circuited. For example, the sum of the power losses of the transistor 5 and the resistor 2 at the time of a short circuit is W=vi×■c Where, W;) The sum of the power losses of the transistor 5 and the resistor 2 vi: Input voltage ■c: The resistor 2 and the transistor 4 The cholera current of transistor 5 is limited by .

As described above, the conventional power supply circuit has a problem in that if the output continues to be in an overcurrent or short-circuited state, the power loss of the transistor 5 becomes large, and the heat generated becomes large, leading to damage.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a power supply circuit that controls the output regardless of whether the power source is a positive or negative output. A transistor that detects a drop in the output voltage and shuts it off is provided in series with the output terminal, and a circuit section that shuts off input and output in the event of an overcurrent or short circuit at the output terminal is connected.

When there is an abnormality on the output side such as overcurrent or short circuit, the base circuit of the first transistor is interrupted by cutting off the base current of the third transistor connected between the first transistor and the second transistor. Shut off, input side device,
Protect output devices and power supplies.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG.

Note that the same parts as in FIG. 2 are given the same reference numerals. 3
．． 6 is a resistor for biasing the transistor 5, 9.10 is a resistor for output voltage detection, 11 is an input terminal for an output on/off signal, 13 is a load resistor, and 15.17 is a transistor 16.
This is the bias resistor.

When the input power supply 1 is applied to the input terminal (input terminal 20), the transistor 5 (
A voltage is applied to the emitter of the first transistor.

At the same time, when an on signal is input to the on/off signal terminal 11 of the control circuit 8, the transistor 7 (second transistor) is driven.

When transistor 7 is driven, transistor 16 (third
The potential at the emitter of transistor 16 decreases, the base of transistor 16 is biased through capacitor 14 and resistor 17, and transistor 16 is turned on. Before the charging current of the capacitor 14 finishes flowing, the transistor 5 is driven and a voltage is outputted to the output terminal, and the transistor 16 is continuously activated by the voltage through the constant voltage diode 18, the reverse current prevention diode 19, and the resistor 17. It turns on.

Next, when an overcurrent state occurs, the transistor 4 is driven by the voltage drop across the overcurrent detection resistor 2, and the line transistor 5 is underdriven, causing the output voltage to drop. When the output voltage falls below the voltage of the constant voltage diode 18, the drive of the transistor 16 is lost and the transistor 16 is cut off. Accordingly, the transistor 5 is also cut off to prevent heat generation in the event of an abnormality (overcurrent or short circuit).

Furthermore, even when the control circuit 8 drives the transistor 7 using an on/off signal (signal input terminal 11) after startup, the same operation and drop as described above occur.

Effects As described above, the cut-off circuit of the power supply device of the present invention is activated by the charging current of the capacitor, and after activation is equipped with a transistor that is driven by the output voltage, so that it can be shut down in the event of an abnormality (overcurrent or short circuit). In addition, protection and safety of the input and output side devices of the power source can be ensured, and heat generation of the power source can also be prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit explanatory diagram of one embodiment of the cutoff circuit of the power supply device of the present invention, and FIG. 2 is a circuit explanatory diagram of a conventional power supply device. 1: Input power supply 2: Overcurrent detection resistor 3.6: Bias resistor for transistor 5 4: Overcurrent protection transistor 5: Transistor that controls output (first transistor) 7: Transistor that controls transistor 5 (
8: Control circuit 9.10: Output voltage detection resistor 11: Output on/off signal input terminal 12: Output terminal 13: Load resistor 14: Capacitor for starting transistor 16 15.17
: Bias resistor for transistor 16 16: Transistor that cuts off transistor 5 (third transistor) 18: Constant voltage diode for output voltage detection 19: Backflow prevention diode 20: Input terminal

Claims (1)

[Claims] It has a 4-terminal circuit network with 2 input terminals and 2 output terminals, an overcurrent detection resistor and a first transistor for output control are connected to the input/output line, and the base circuit of the transistor is driven by a signal from the control circuit. In a power supply device in which a second transistor is connected, a third transistor is connected between the first transistor and the second transistor, and is activated by the charging current of the capacitor and is shut off when the output voltage decreases.
A cut-off circuit for a power supply device, characterized in that a transistor is connected thereto.