JPS62178120A - Overcurrent protective circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] When an overcurrent occurs due to a load failure or other condition in a power supply device, a drop in load voltage is detected and the power output is transferred from a normal path to a protection path with current limits. This switch protects the power supply and load.

[Industrial application field]

The present invention relates to an improvement in an overcurrent protection circuit in a power supply device.

If a current exceeding the permissible current flows from the power supply due to a failure in various component circuits of the device, not only the power supply is destroyed, but the load side also suffers damage such as burnout. Therefore, if an overcurrent flows, it is necessary to limit or cut off the supplied current.

Fuses are used in small-capacity power supplies, but the fusing current value varies, the fusing time is long, and parts need to be replaced each time. Therefore, overcurrent protection allows instantaneous current limiting and eliminates the need to replace parts. It is requested that the circuit be provided.

[Conventional technology]

There are fuses, circuit breakers, etc. for overcurrent protection, but there are no circuit breakers that are small enough to be mounted on a printed board, and fuses are used exclusively in the field of several amps or less.

[Problem that the invention seeks to solve]

Conventionally used fuses are simple, but the blowing current value is larger than the displayed current value, the current value varies, and the blowing time is long, so there are cases where it is unsafe for both the load side and the power source side. In addition, there are problems in terms of economy and man-hours because parts must be replaced during restoration.

[Means for solving problems]

FIG. 1 is a principle diagram of the overcurrent protection circuit of the present invention. Reference numeral 1 indicates a supply section that supplies the load current under normal conditions, 2 indicates a protection section that supplies limited current to the load, and 3 detects a drop in load voltage when an overcurrent flows and controls supply section 1 and protection section 2. This is a detection unit that performs

[Effect]

The detection section 3 detects a voltage drop due to overcurrent, controls the supply section 1 to cut off the power output, and also controls the protection section 2 to supply the limited current to the load.

In this way, an overcurrent protection circuit is obtained in which the load current is instantaneously limited to a safe current value, the power source and the load are safely protected, and no part replacement is required for restoration.

〔Example〕

The present invention will be specifically explained below with reference to illustrated examples.

FIG. 2 is a diagram of an overcurrent protection circuit according to an embodiment of the present invention.

In the figure, the supply section 1 consists of a transistor Ql and a resistor R5, and the protection section 2 consists of transistors Q2. Q3, resistance R
2 to R4, the detection section 3 is a transistor QO, a diode D
, resistors RO and R1.

Normally, transistor Q1 is turned on and load current flows through the transistor, but when an overcurrent flows,
The voltage drop across the resistor RO increases, the base voltage of the transistor QO goes high, and the transistor QO is turned on, so the base voltage of the transistor Q1 goes low, the transistor RO1 is turned off, and the power output is cut off.

Furthermore, when transistor QO is turned on, the base voltage of transistor Q3 becomes low level, turning on transistor Q3. Therefore, the base voltage of transistor Q2 becomes high level and turns on, so the load current is limited by resistor R4, and the load and power supply is protected.

When the fault disappears and the current returns to normal, the voltage drop across resistor RO returns to its normal value, so transistor QO turns off.
Thereafter, the applied transistors are sequentially returned to their original states, and the circuit is automatically restored and the load current is again supplied via the transistor Q1.

〔Effect of the invention〕

As explained above, the overcurrent protection circuit of the present invention detects overcurrent, instantly limits the power output to a current value that is safe for the load and power supply, and protects the power supply and load circuit. There is. In addition, there is no need to replace parts and therefore no man-hours, so there is an economical effect.

[Brief explanation of drawings]

FIG. 1 is a principle diagram of the overcurrent protection circuit of the present invention, and FIG. 2 is a diagram of the overcurrent protection circuit of the present invention. In the figure, 1 is a supply section, 2 is a protection section, 3 is a detection section, QO-03 is a transistor, D is a diode, and RO-R5 is a resistor.・-;: ・r.・Interest

Claims (1)

[Claims] A power supply device includes: a supply unit (1) that allows a load current to flow during normal conditions; a protection unit (2) that causes a limited current to flow through the load during abnormal conditions; and a protection unit (2) that monitors the load current to detect an abnormality. A detection section (3) is provided, and when the detection section (3) detects an abnormality, the supply of load current is switched from the supply section (1) to the protection section (2) and supplied to the load. Current protection circuit.