JPH0630523A - Overcurrent preventive circuit - Google Patents

Abstract

PURPOSE:To provide a high response, highly reliable overcurrent preventive circuit at low cost by simplifying the circuitry. CONSTITUTION:The overcurrent preventive circuit comprises a switch 4 for interrupting power supply 1 to a motor drive system 2, and a transistor 5 for detecting potential difference between the source and drain of the switch 4 and interrupting the switch 4. When current supply from the power supply 1 to the motor drive system 2 exceeds a predetermined level because of the deterioration or short circuit of the motor drive system 2, the transistor 5 detects potential difference from voltage drop caused by overcurrent and interrupts the switch 4 thus interrupting current supply to the motor drive system 2 and stopping operation thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent prevention circuit for preventing overcurrent due to deterioration or short circuit of a motor drive circuit or the like.

[0002]

2. Description of the Related Art Conventionally, a switch inserted between a power supply and a load is constantly monitored by a microcomputer or the like when an abnormality such as an overcurrent due to deterioration or a short circuit occurs between the power supply and the load. Was shut down to deal with the load abnormality. For example, in a drive circuit of a power supply and a motor, a voltage drop of a resistor inserted serially or in parallel between the power supply and the motor (load) is monitored by a microcomputer using an A / D converter or the like, and abnormal due to overcurrent or the like. When such a voltage drop occurs, the microcomputer shuts off the switch inserted between the power supply and the load.

However, when a microcomputer shared with other operating circuits is used, there is a large delay from the detection of an abnormality to the handling thereof, which may prevent the occurrence of an accident. In addition, abnormal loads may affect the operation of the microcomputer itself and prevent corrective actions. Therefore, if a dedicated microcomputer is provided to deal with this, the cost will increase. It was

[0004]

As described above, when an abnormality such as an overcurrent occurs between the power supply and the load, a microcomputer or the like which has always been conventionally monitored is inserted between the power supply and the load. The switch was shut down to deal with the load abnormality.

However, when a microcomputer shared with other operating circuits is used, a large delay occurs from the detection of an abnormality to the countermeasure, an accident cannot be prevented, and an abnormal load causes an operation of the microcomputer. There is also a problem in that the device itself may be affected and normal coping operation may not be possible, and if a dedicated microcomputer is provided to deal with this, the cost becomes high. Therefore, an object of the present invention is to provide an overcurrent prevention circuit that is low in cost and has high-speed response and high reliability.

[0006]

An overcurrent prevention circuit according to the present invention is a circuit for supplying a current from a power source according to the impedance of a load, and a field effect transistor connected between the power source and the load. A detecting means for detecting a potential difference between a power supply side terminal and a load side terminal of the field effect transistor; and a transistor for controlling conduction of the field effect transistor according to the potential difference detected by the detecting means, When the current supplied from the power source to the load exceeds a predetermined value, the transistor detects the potential difference generated between the power source side and the load side of the field effect transistor and shuts off the field effect transistor. Is configured.

[0007]

According to the present invention, when the current supplied from the power supply to the load via the field effect transistor exceeds the predetermined value due to overcurrent due to deterioration of the load, short circuit, etc. A transistor detects the potential difference caused by this overcurrent between the power supply side and the load side,
The field effect transistor is cut off to stop the operation of the load.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an overcurrent prevention circuit according to the present invention. That is, a power supply 1 that supplies 24 V, a motor drive system 2 that is a circuit as a load, a capacitor (47 μF / 3) for stabilizing the current supplied to the load.
5V) 3, a P-channel MOS field effect transistor (hereinafter referred to as switch 4, for example, 2SJ183) used as a switch for shutting off an overcurrent, a potential difference between the source and the drain of the switch 4, and the source of the switch 4; A transistor (for example, 2SA1015) 5 for controlling the potential between the gates, a resistor (4.7 kΩ) 6 for limiting a base current when the transistor 5 is in conduction, and a switch 4 when the motor drive system 2 is operating normally. Source that keeps ON state, resistance (10 kΩ) 7 and resistor (12 kΩ) 9 for dividing voltage to obtain potential difference between gates, source of switch 4 so that switch 4 is quickly turned on when power supply 1 is turned on. , The voltage dividing resistance (22kΩ) 8 and the resistance (22kΩ) 10 for obtaining the potential difference between the gates, and the current at the start-up of the power supply 1 are reduced. A capacitor (2.
2 μF / 35 V) 11. The operation in such a configuration will be described.

First, in the switch 4, when the potential difference between the source and the gate is about 10 V, the source and the drain are turned on (ON resistance is about 0.3Ω). That is, when the power supply 1 is turned on, the source is divided by the resistors 7 and 9,
The potential difference between the gates becomes about 10 V, and the source and gate of the switch 4 are turned on.

However, since the load generally has a capacity, the current to the load when the power source 1 is started may be an overcurrent for a moment and the transistor 5 may be turned on to cause a cutoff operation. Resistor 10 to prevent it
With the capacitor 11 and the capacitor 11, a time constant sufficient to avoid an overcurrent at the time of starting the power source 1 is provided to suppress an increase in the gate potential of the switch 4 to stabilize the startup (at this time, the transistor 5). Is on).

Even when the transistor 5 is on, current flows into the capacitor 11 through the resistors 8 and 10, so that the gate potential does not rise rapidly and the potential difference of about 10 V is maintained between the source and gate of the switch 4, The source and drain of the switch 4 are turned on, and current is supplied to the circuit of the motor drive system 2.

When a steady current is supplied to the circuit of the motor drive system 2, the potentials of the source and drain of the switch 4 become almost equal, and the transistor 5 is turned off.
After that, the potential difference between the source and gate of the switch 4 is
The voltage divided by the resistors 7 and 9 changes at about 10 V, and the ON state between the source and the drain of the switch 4 is maintained.

When an abnormality or a short circuit occurs in the circuit of the motor drive system 2 and an overcurrent starts to flow, the potential difference between the source and the drain of the switch 4 begins to widen,
When the potential difference becomes about 0.6 V, the transistor 5 is turned on.

When the transistor 5 is turned on, the gate potential of the switch 4 rapidly rises from the potential held at a certain value by the capacitor 11 until it becomes equal to the source potential. Therefore, the rise time of the gate potential until it becomes equal to the source potential by the holding potential of the capacitor 11 is shortened.

The switch 4 is activated by the rapid rise of the gate potential.
The potential between the source and the gate of the switch 4 becomes equal, the source and the drain of the switch 4 are turned off, and the motor drive system 2
The supply of current to is quickly stopped.

As described above, according to the above embodiment,
By handling the overcurrent at the time of load abnormality by using the field effect transistor instead of the microcomputer, the circuit is directly cut off, high-speed response and high reliability are possible, and further, the cost is reduced by simplifying the circuit scale. Can be realized.

[0018]

As described above in detail, according to the present invention,
It is possible to provide a low-cost, high-speed response and highly reliable overcurrent prevention circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram schematically showing an overcurrent prevention circuit according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Power supply, 2 ... Motor drive system, 3, 11 ... Capacitor,
4 ... Switch, 5 ... Transistor, 6, 7, 8, 9, 1
0 ... resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuyoshi Tagami 70 Yanagicho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Yanagimachi Factory

Claims (1)

[Claims] 1. A circuit for supplying a current from a power source according to the impedance of a load, comprising: a field effect transistor connected between the power source and the load; and a power source side terminal and a load side terminal of the field effect transistor. A detection means for detecting a potential difference between the two and a transistor for controlling conduction of the field effect transistor according to the potential difference detected by the detection means are provided, and a current supplied from the power source to the load has a predetermined value. An overcurrent prevention circuit, characterized in that when the value exceeds a value, a potential difference generated between the power source side and the load side of the field effect transistor is detected by the transistor and the field effect transistor is cut off.