JPS6281923A - Overcurrent detector 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 (Field of the Invention) The present invention relates to an overcurrent @λ[1 circuit suitable for driving a load with one to transistors.

(Summary of the Invention) In this invention, an overcurrent is detected and overridden by comparing the saturation voltage between the main terminals of the load IW and the transistor with a reference voltage, and the output residual voltage and heat generation amount are reduced. This will have the effect of minimizing

(Prior art and its problems) Conventionally, when driving a load with a transistor, in order to detect an overcurrent in the load, as shown in FIG.
It is customary to connect a current detection resistor 2 in series with the load driving transistor, and to discriminate the level of the voltage across the terminals of the resistor 2 using a comparator 3.

Note that 4 and 5 are photocouplers for insulating and separating the control circuit and the main circuit, respectively.

However, in such an overcurrent detection circuit,
Since a voltage drop occurs due to the current detection resistor 2, the residual voltage from the output side becomes high, and the heat generated by the resistor 2 is large, resulting in many problems such as restrictions on thermal design and mounting design. Ta.

(Objective of the Invention) An object of the invention is to provide an overcurrent detection circuit which has a low residual voltage from the output side and generates little heat.

(Structures and Effects of the Invention) In order to achieve the above object, the present invention is characterized in that overcurrent is detected by comparing the saturation voltage between the main terminals of the load driving transistor with a reference voltage. .

According to such a configuration, the saturation residual voltage does not become high, the amount of heat generated can be suppressed to a minimum, and restrictions on thermal design and packaging design can be reduced.

Furthermore, since the voltage at the output terminal is monitored when the transistor is off, it is also possible to detect load disconnection.

(Description of Embodiments) FIG. 1 is a circuit diagram showing an example of an overcurrent detection circuit according to the present invention.

As shown in the figure, in this circuit, an overcurrent in the load circuit is detected by level-discriminating the voltage between the emitter and collector (between the main terminals) of the load driving transistor 1 using a comparator 6.

Note that 7 and 8 are photocouplers for insulating and separating the main circuit and the control circuit, respectively.

Next, the load on/off operation is performed as follows. If the output 0N10FF signal is “BI”, photocoupler 7
is turned on, and load drive transistor 1 is turned on. On the other hand,
If the output ON/OFF signal is "T1", the photocoupler 7 is turned off and the transistor 1 is turned off.

Next, the overcurrent detection operation is performed as follows.

The relationship between the current IC flowing through the collector of transistor 1 and the collector-emitter saturation voltage vcε(sat) is as follows:
As shown in Figure 2, as Ic increases, Vcg (Sar
) has the characteristic of increasing the rate of increase.

When this V e r = (sat) is compared with the preset reference voltage ref by the comparator 6, when an overcurrent flows through the transistor 1, the output of the comparator 6 becomes "'", and the detection signal becomes " It becomes 'bi'.

Next, the load disconnection detection operation is performed as follows. When the transistor is off and the load and load power supply are connected properly, a voltage above a certain level is applied to the collector of the transistor. Therefore, the output of the comparator 6 and the detection signal are both "the same".If
When the load is disconnected or the load power supply is turned off, the collector of the transistor 1 becomes non-voltage, the comparator 6 becomes ``H'', and both detection signals become ``H''.

With the above-described operation, overcurrent detection and load disconnection detection can be performed simultaneously by the method shown in the flowchart of FIG.

Note that although the above embodiments have been explained using bipolar transistors, it goes without saying that the same explanation can be made with power MOS transistors and the like.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of an overcurrent detection circuit according to the present invention, and Fig. 2 shows IC-VcE (sat) of a transistor.
FIG. 3 is a graph showing a characteristic curve, FIG. 3 is a flowchart explaining the operation of the device of the present invention, and FIG. 4 is a circuit diagram showing a conventional example. 1...Load driving transistor 6...Comparator 1m

Claims (1)

[Claims] (1) An overcurrent detection circuit that detects overcurrent by comparing the saturation voltage between the main terminals of a load driving transistor with a reference voltage.