JPS5888908A - Protective device for transistor - Google Patents

Abstract

PURPOSE:To realize the protection simply and inexpensively, by short-circuiting the base and emitter of a transistor (TR), when a voltage between the collector and emitter reaches a prescribed value or over. CONSTITUTION:If a load 11 is short-circuited and an overcurrent flows to a TR1, the collector current of the TR1 is increased and a collector-to-emitter voltage is increased at the same time. Thus, the base current of a TR2 is increased and the TR2 is turned on. After a specified delay time with a saturable reactor 3, a collector current flows to the TR2, a current from an emitter of a TR7 becomes the collector current of the TR2 to protect the TR1 by interrupting the base current of the TR1 and turning off the TR1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device that protects a transistor from overcurrent.

Conventionally, an overcurrent detection device used in this type of protection device is connected in series to the collector or emitter of a transistor to be protected. When an overcurrent is detected, the pace control circuit cuts off the pace current of the relevant transistor, thereby cutting off the collector current.

However, when a current transformer is used as a current detection device in such a conventional device, the current transformer is large and expensive.
When using a voltage drop caused by a resistor, there are drawbacks such as large power loss in the resistor, complicated circuit configuration, and high cost.

The present invention has been made to eliminate the above-mentioned drawbacks of conventional devices, and an object of the present invention is to provide a small and inexpensive transistor protection device.

The present invention will be described in detail below with reference to the drawings.

Figure 1 is a connection diagram showing one embodiment of the present invention, in which (1) is the transistor to be protected, +2
1t! The switch transistor, (3) is a saturable reactor, (4) e (5) e te+ are each a resistor, (71II2 control transistor, +81 Fi control device, 19+ and fil are each a power supply, and αυ is a load.

In addition, Fig. 2 is a waveform diagram showing the waveforms of each part in Fig. 1, the horizontal axis indicates time, and Fig. 2 (a) Fi) transistor (7).
(b) is the base current of transistor (1), (C) is the collector current of transistor (1), (d) is the collector-to-emitter voltage of transistor (1), FIG. 5(e) shows the base current of transistor (2), and FIG. 2(f) shows the collector current of transistor 12+.

Next, the operation of the circuit shown in FIG. 1 will be explained using FIG. 2. Before time t1 in FIG. 2, the transistor (7) is in the off state, so the base current of the transistor (11) does not flow and the transistor (1) is in the off state. At that time, the voltage between the collector and emitter of the transistor (11) is It is equal to the voltage of a[, and this voltage is equal to the voltage of resistor 1
The voltage is divided by 41 and 151 and applied to the base of transistor (2), and the base current of transistor (2) is as shown in FIG. 2(e). However, since the transistor (7) is in the off state, the collector current of the transistor (2) (FIG. 2(f)) does not flow.

Next, at the point in time in FIG. 2, a base current is supplied from the control device (81) to the transistor (7). Therefore, the transistor TRI i'i is turned on and the collector current shown in FIG. 2(a) flows. All of the collector current becomes the base current of the transistor (1) (Fig. 2 (b)) and does not branch to the saturable reactor (3). This is due to the current delay effect of the saturable reactor (3). Therefore, transistor (1) turns on and the second
The collector current shown in Figure (e) is from the power source → load αυ → collector of transistor (1). Because of the voltage drop due to the emitter of transistor (1) and current load αυ, the voltage between the collector and emitter of transistor (1) becomes almost O. (FIG. 2(d))) The transistor 12) is cut off (see FIG. 2(e) and (f)). In this way, when the transistor (1) is in a steady on state, the series circuit of the saturable reactor (3) and the switching transistor (2) does not have any influence 411 on the base current control of the transistor (1). .

Next, suppose that an overcurrent flows through the transistor +11 because the load αυ is short-circuited at time t3. Transistor (1
1's collector current (FIG. 2(C)) increases, and at the same time, its collector-emitter voltage (FIG. 2(d)) increases. Therefore, the base current of transistor (2) (second
(e)) increases and transistor (2) turns on. At time t1 after a predetermined delay time due to the saturable reactor (31), the collector current of the transistor (21 (
Figure 2 (f)) flows, and the current from the emitter of transistor (7) becomes the collector current of transistor (2), cuts off the base current of transistor (1), turns off transistor (11), and maintains transistor (11). do.

FIG. 3 is a connection diagram showing another embodiment of the present invention. The same reference numerals as in FIG. 1 indicate the same or corresponding parts. In the embodiment shown in FIG. ) by shorting the base and emitter of transistor (7).
The base current is cut off, but the other operations are the same as in the case of FIG. 1, so redundant explanation will be omitted.

In addition, in the above embodiment, the switching transistor (21) is not limited to a transistor, but may be a thyristor,
G T O (gate turn-off zl*yr
istor), FET (field effect)
It is clear that a general switching device such as a ttransistor may be used, and the use of a saturable reactor (31) is not limited to a saturable reactor, but a general current delay device such as an ordinary glue reactor may be used.

As described above, according to the present invention, it is possible to obtain a transistor storage device that has a simple circuit configuration, is small in size, and can be manufactured at low cost.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing one embodiment of this invention, Fig. 2 is a waveform diagram showing waveforms of each part of the circuit in Fig. 5, and Fig. 3 is a connection diagram showing another embodiment of this invention. . ill...Transistor to be protected, +21.
...Switch transistor, (3)...Saturable reactor. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Shin Kuzuno - Figure 2 (a) Figure 3

Claims (1)

[Claims] A means for measuring the voltage between the collector and emitter of the transistor to be protected, a switch device that turns on when the voltage between the collector and emitter reaches a predetermined value or more, and a current delay device connected in series with the switch device. The pace of the transistor that is subject to the above protection depending on the connected circuit,
A protection device for a transistor, comprising: means for short-circuiting a voltage between emitters only during a period when the switch device is in an on state.