JPS6037018A - Current limiter - Google Patents

Abstract

PURPOSE:To attain an effective protecting action for a power transistor of a power supply circuit without flowing a large current, by dividing the limiter value into two steps in order to reduce the amount of the current flowed when a load is short-circuited. CONSTITUTION:In a steady mode a switch 19 is closed and a current of (I1+I2) flows to a resistance 15 of an operational amplifier 16. At the same time, the voltage corresponding to said current value is applied to the amplifier 16 in the form of the reference value. As a result, a limiter works at a level shown by A. Then the switch 19 is opened by the output of a comparator 26 when the output voltage is lowered down to a level shown by B. Thus the limiter current flowing to the resistance 15 is cut down to half, for example, as shown at a point C. Therefore the current value is reduced to half in case a load has a short circuit (the output voltage set at zero). This can protect effectively a power transistor, etc. of a power supply circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current limiter device that protects an output terminal of a circuit using an IC or the like from overcurrent caused by a short circuit accident.

For example, from an electronic control unit composed of a circuit including an IC, etc., to an external device to be controlled,
When power is supplied, a drive signal for an external device is output from an output terminal provided for the unit. In this case, for example, the conductive wire used in this output circuit may become jammed, and if a fault such as a short circuit occurs, an accident may occur that destroys the power transistor in the unit. Therefore, in order to protect this knocker transistor, the current flowing through this transistor is detected and a limiter is applied.

Conventionally, the following types of current limiter devices have been considered, for example. That is, the current value flowing through the circuit is compared with a specified reference current value, and when a short circuit current is flowing, this is detected and the circuit is controlled to be opened. However, since devices with this type of configuration are designed to perform effective protection only in the event of a short circuit, a very large current will flow even transiently in the event of a short circuit. . Also,
If the reference current value is limited in order to avoid such a problem, the load circuit will not be able to take out the sufficient current required, resulting in a current shortage, and the load control by the electronic control unit will be difficult. This makes it difficult to implement over a wide range of areas.

This invention was made in view of the above points. For example, it is possible to sufficiently suppress heat generation when the output of a power transistor that draws output current from an electronic control unit is short-circuited. The present invention aims to provide a current limiter device that can maintain sufficient tolerance.

That is, in the current limiter device according to the present invention, by dividing the limit value into two stages, for example, the amount of current can be reliably reduced in the event of a load short-circuit without reducing the current tolerance. It is meant to be.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows its configuration. The output current from a DC power supply 11 is supplied to an output terminal 14 via a resistor 12 and a transistor 13 that controls opening and closing of this current circuit. Although not shown in the figure, a load circuit is connected to. One end of the resistor 12 on the power supply 1 side is further connected via a resistor 15 to the positive terminal of an operational amplifier 16 (hereinafter referred to as an operational amplifier) that operates to compare voltages, and the other end of the resistor 12 is connected to the positive terminal of an operational amplifier 16 (hereinafter referred to as an operational amplifier). Connect to the reverse side terminal of 16. This resistor 12.15 is used to detect the voltage corresponding to the current, and the resistor 15 is connected to the first and second constant current circuits 17.
．． The constant current defined by 18 is set to flow.

In this case, the first and second constant current circuits 17 and 18
are provided in parallel, and the first constant current circuit 17 is selectively cut off by a switch 19.

That is, when the switch 19 is closed, r is applied to the resistor 15.
The currents I, +I, J flow, and when the switch 19 is open, the currents "■," flow. Therefore, the potential of the positive terminal of the operational amplifier 16 is determined by the amount of current flowing through the resistor 15.

The pace of the transistor 13 is controlled by a control transistor 20.
0 pace, a signal obtained by inverting the output signal from the fourth amplifier 16 using the inverter 21 and an operational amplifier 22.
synthesizes and supplies the output signals from the A constant voltage is created by the non-inverting amplification amount of this operational amplifier.

Further, the reference potential and the output potential are compared by a comparison circuit 26, and the switch 19 is controlled to be opened when the output potential drops to B shown in FIG.

The current limiter device configured in this manner detects the voltages of the resistors 12 and 15 and applies a limiter. That is, a constant current is drawn from the resistor 15 to maintain a constant voltage, and the operational amplifier 16 compares the voltage corresponding to the voltage drop caused by the current flowing through the resistor 12 with the above-mentioned constant voltage.

In other words, when a limiter current higher than the current flowing through the resistor 15 flows through the resistor 12, the output of the operational amplifier 16 becomes a low (H) level, and therefore the output from the inverter 2 becomes a low (L) level. ) level, turning off the emitter and collector of the transistor 20. Therefore, the transistor 13 is also turned off, and the output current is cut off. For example, if there is a short circuit on the load side, the transistor 13 cuts off the power output and protects the power supply circuit.

Here, in the steady state, the switch 19 is closed and a current of r11+I2J flows through the resistor 15 of the operational amplifier 16, and the electrical ratio corresponding to this current value is given to the operational amplifier 16 as a reference value. . Therefore, in the first stage, the limiter operates at the level indicated by A in FIG.

When the output voltage drops to the voltage shown in FIG. 2B, the switch 19 is opened by the output of the comparator circuit 26, and the limiter current flowing through the resistor 15 is changed to, for example, as shown by the zero point in the figure. Make it half. Therefore, for example, when the load is short-circuited (output voltage is zero)
The current is halved, which can effectively protect power circuits such as power transistors.

Note that in a conventional device that does not limit the limiter current, the current when the load is short-circuited is at point D.

Incidentally, in the above embodiment, the operational amplifier 16°22 may be constructed as a voltage comparator circuit.
Further, it goes without saying that the switch 19 may be constructed of a semiconductor switch or the like. Further, the limiter current switching is not limited to two stages, but may be configured in a larger number of stages, and may be configured to be continuously variable controlled as necessary.

As described above, according to the present invention, even if a short circuit or the like occurs in a load circuit, for example, it is possible to perform an effective protective operation without unnecessarily flowing a large current to a noyawer transistor that constitutes a power supply circuit. At the same time, it is possible to maintain sufficient current tolerance for the load.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating a limiter device according to an embodiment of the present invention, and FIG. 2 is an operating characteristic diagram illustrating the operation of the device. 11... DC power supply, 12.15... Resistor (for current detection), 13... Transistor, 16.22... Operational amplifier, 17.18... Constant current circuit, 19
...Switch, 26...Voltage comparison circuit.

Claims (1)

[Claims] A voltage signal is supplied from one end of a first resistor circuit connected in series with the power supply circuit via a second resistor circuit, and the voltage signal from the other end of the first resistor circuit is supplied as a comparison voltage. a comparison circuit, a constant current circuit that controls the amount of current flowing through the second resistance circuit in at least two stages, a variable control element that is provided in series with the power supply circuit and controls the amount of current that flows, and a variable control element that controls the amount of current flowing through the second resistance circuit; means for controlling the variable control element in accordance with the output of the circuit to be compared; and means for controlling the constant current circuit by switching the constant current circuit in a state where the output current increases by comparing the output current with a set reference value; A current limiter device comprising means for reducing the amount of current flowing through a resistor circuit.