JPH03240112A - Overcurrent protecting circuit - Google Patents

Abstract

PURPOSE:To prevent an output circuit from being destroyed by providing a 2nd breaking circuit which controls the input of an error amplifier, a 3rd breaking circuit which breaks the output circuit and a drive circuit, and an overcurrent detecting circuit. CONSTITUTION:A start circuit consists of transistors TR Q1 - Q4 and a resis tance R1. A 1st breaking circuit consists of the resistances R2 and R3, a 3rd breaking circuit consists of a TR Q5 and a resistance R4, and a 2nd breaking circuit consists of a TR Q6 and a resistance R5. Then an output circuit consists of the TR Q8 and Q9, a resistance R7, and a current source IS, and an overcurrent detecting circuit consists of the TR Q10 and Q11. The 2nd breaking circuit controls the input of an error amplifier GA so as to break the output circuit and the amplifier GA when an overcurrent flows to the output circuit. Then the 3rd breaking circuit breaks the output circuit and the start circuit. These 2nd and 3rd breaking circuits are simultaneously actuated. Thus it is possible to prevent the output circuit from being destroyed by the overcurrent.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to an overcurrent protection circuit that prevents the output circuit from being destroyed by overcurrent when an overcurrent flows through the output circuit of a regulator circuit. It is something.

(b) Conventional technology In the case of a regulator circuit that obtains a constant output by using a PNP type output transistor, since the drive capacity of the PNP type output transistor is small, the output transistor is prevented from being destroyed by overcurrent. They generally do not have an overcurrent protection circuit.

(c) Problems to be Solved by the Invention However, in the conventional regulator circuit, when the output of the output transistor is short-circuited to earth for measurement, maintenance, etc., an overcurrent flows through the output transistor. There was a risk that the output transistor would be destroyed by overcurrent. In particular, in a regulator circuit implemented as an IC, there is a problem that the IC itself may be destroyed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an overcurrent protection circuit that can prevent an output transistor from being destroyed by overcurrent by adding only a few elements.

(d) Means for Solving the Problems The present invention has been made to solve the above problems, and includes a starting circuit for operating an output circuit, and a starting circuit for operating the output circuit based on the output of the output circuit. a first cutoff circuit that cuts off the output circuit and the starting circuit when the output is greater than a predetermined value; a detection circuit that detects output fluctuations of the output circuit; and a detection circuit that detects an error between the output of the detection circuit and a reference value. In a regulator circuit that includes an error amplifier for detecting and a drive circuit to which the error output of the error amplifier is negatively fed back and operates the output circuit, the regulator circuit controls the output of the output circuit to a constant value. a second cutoff circuit that controls the input of the error amplifier to cut off the output circuit and the error amplifier when an overcurrent flows into the output circuit; a third cutoff circuit that cuts off the circuit, and an overcurrent detection circuit that detects that an overcurrent flows into the output circuit and simultaneously operates the second cutoff circuit and the third cutoff circuit; An overcurrent protection circuit comprising: an overcurrent protection circuit that prevents the output circuit from being destroyed by overcurrent.

(e) Effect According to the present invention, in the overcurrent protection circuit described in item (d) above, when the output circuit is short-circuited for measurement, maintenance, etc., and an overcurrent flows through the output circuit, the output circuit Is it applicable so that the error amplifier is cut off? a second cutoff circuit that controls the A-difference amplifier; and a third cutoff circuit that cuts off the output circuit and the startup circuit.
The cutoff circuit operates simultaneously, thereby preventing the output circuit from being destroyed by overcurrent.

(f) Example The details of the present invention will be specifically explained with reference to the drawings.

The drawing is a circuit diagram showing a low saturation regulator circuit using the overcurrent protection circuit of the present invention.

In the drawings, transistors Q , Q , Q , Q ,
and resistor R4 constitute a starting circuit, resistors Rt and Rr constitute a first cutoff circuit, transistor Q and resistor R
A constitutes a third cutoff circuit, transistor Q6 and resistor R6 constitute a second cutoff circuit, transistor Q constitutes a drive circuit, PNP type transistors Q, Q, .
Resistor R2 and current source Is constitute an output circuit, and resistor R2
,R, is the detection circuit I! In addition, the transistor Q1.
Q and l constitute an overcurrent detection circuit. Furthermore, the reference voltage V
The reference voltage generating circuit RV that generates IIEF is set to operate when the power supply voltage V reaches the rated value, and the resistor Rt Rx is set to operate when the power supply voltage ~'8 reaches the rated value. is set to a value that turns on. Furthermore, in the error amplifier GA, the inverting (-) input terminal is connected to the output of the reference voltage generation circuit RV, the non-inverting (+) input terminal is connected to the voltage dividing point of the resistors R, R, and the output terminal is connected to the output of the reference voltage generating circuit RV. It is connected to the base of Q.

First, when the power supply voltage VIN rises to the base-emitter voltage of the transistor Q1, the current mirror-connected transistors Q, Q, and transistor Q4 are turned on. It is pulled to ground potential through the collector-emitter paths of transistors Q and Q, and is turned on. Furthermore, the power supply voltage V(
When H rises to its rated value, the resistance R! increases in proportion to the collector voltage of transistor Q! Since the divided voltage value of Rs increases, the transistor Q is turned on, and the base of the transistor Q is pulled to the ground potential through the collector-emitter path of the transistor Q, and the transistor Q is turned off. That is, the output circuit and the starting circuit are cut off, and the output circuit operates without being affected by the starting circuit. And resistance R
, R, increases in proportion to the collector voltage of transistor Q, so the error amplifier GA uses the reference voltage VREF.
An error voltage corresponding to the difference between the resistors R and the divided voltage values of the resistors R and R is output, and the error voltage is negatively fed back to the base of the transistor Q.

Therefore, transistor Q8 is the emitter of transistor Q.
Therefore, the collector voltage of the transistor Q (ie, the output voltage V.UT) is controlled to a constant value.

Next, in the regulator circuit that operates as described above,
If the collector of transistor Q is short-circuited to earth for the purpose of measurement, maintenance, etc., an overcurrent will flow into the collector-emitter path of transistor Q. Here, transistors Q, Q,. Q
11 is connected as a current mirror. Therefore, when the base current of the transistor Q increases due to the overcurrent, the base current of the transistor Q11 also increases, so that the transistor Q6 is turned on. Therefore, the inverting input terminal of the error amplifier 5GA is grounded via the collector-emitter path of the transistor Q6, and the error voltage corresponding to both input voltages, that is, the error voltage for operating the transistor Q in a saturated state, is applied to the error amplifier. Output from GA. Therefore, transistors Q and Q are turned off as the base of transistor Q is pulled up to the power supply potential via the collector-emitter path of transistor Q7. At the same time, transistor Q,
When the base current of transistor Q1G increases due to the overcurrent, the base current of transistor Q1G also increases, so that transistor Q is turned on. Therefore, even if transistor Q is turned off as transistor Q is turned off, transistor Q4 remains off because transistor Q is turned on. Therefore, the starting circuit and the output circuit remain cut off, and transistors Q, Q, are not turned on. From the above, it can be seen that the overcurrent is at the collector of transistor Q.
Even if the current flows to the emitter path, the transistor Q is reliably turned off, so that the transistor Q can be prevented from being destroyed by overcurrent. In particular, when the circuit shown in FIG. 1 is integrated into an IC, the IC itself can be protected.

(G) Effects of the Invention According to the present invention, it is possible to prevent the output transistor from being destroyed by overcurrent by adding only a few elements, and the reliability of the regulator circuit is improved. Furthermore, the regulator circuit using the circuit of the present invention has advantages such as being suitable for IC implementation.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing is a circuit diagram showing an overcurrent protection circuit of the present invention. Q1-Q11・Transistor, R1-R1...
Resistor, RV, base $, pressure generating circuit, GA, error amplifier, Is... current source.

Claims (2)

[Claims] (1) a starting circuit that operates an output circuit; a first cutoff circuit that cuts off the output circuit and the starting circuit when the output of the output circuit is equal to or higher than a predetermined value based on the output of the output circuit; a detection circuit that detects output fluctuations of the output circuit; an error amplifier that detects an error between the output of the detection circuit and a reference value; and an error output of the error amplifier that is negatively fed back;
A regulator circuit that has a drive circuit that operates the output circuit and controls the output of the output circuit to a constant value, wherein when an overcurrent flows to the output circuit, the regulator circuit shuts off the output circuit and the error amplifier. a second cutoff circuit that controls the input of the error amplifier to ensure that the input of the error amplifier is controlled, and a third cutoff circuit that cuts off the output circuit and the starting circuit when an overcurrent flows to the output circuit; an overcurrent detection circuit that simultaneously operates the second cutoff circuit and the third cutoff circuit by detecting that the current has flowed, and the output circuit is prevented from being destroyed by the overcurrent. Features an overcurrent protection circuit. (2) The second cutoff circuit controls the reference value input to the error amplifier in order to prevent destruction of the output circuit when an overcurrent flows into the output circuit. 1
) Overcurrent protection circuit described.