JPS59163616A - Protecting circuit of transistor - Google Patents

Abstract

PURPOSE:To protect a transistor TR from its breakdown by connecting the TR in parallel to a large current TR and setting the collector-emitter voltage of the TR at a level lower than the prescribed value. CONSTITUTION:A DC power supply 100 is connected in parallel to a load 104, and a TR101 for large current is connected in series between the supply 100 and the load 104. A diode 102 is connected in parallel to the TR101, and the collector-emitter voltage of the TR101 is set at a level lower than the protectable value. An overcurrent passes not through the TR101 but through the diode 102 when the power supply is started or in an overcurrent mode. Thus the TR101 can be protected from its breakdown.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for transistors connected in series to a power supply circuit.

The present invention connects a diode with a large current capacity between the collector and emitter of the transistor, and bypasses the current exceeding the allowable collector current of the transistor through the diode that is resistant to surge currents. The purpose is to protect the transistor from destruction in the event of overcurrent.

SUMMARY OF THE INVENTION The present invention provides a circuit in which a gold transistor is inserted in series with a power source, in which at least one diode or a series of elements that produce a constant voltage potential drop are connected between the collector and emitter of the transistor. and a transistor collector current detection circuit and a transistor drive circuit, and when the collector current detection circuit detects a current equal to or higher than a predetermined current value, the transistor drive circuit detects the operation of the transistor. The transistor protection circuit is characterized in that the condition is shifted to the cutoff direction, thereby causing at least a part of the collector current to be detoured through the element array.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the invention will now be described with reference to the electronic schematic diagram of FIG. 1 and the graphical representation of FIG.

Reference numeral (100) in FIG. 1 is a power source, for example a DC power source. (104) is a load, which is connected in parallel to the power supply (Zoo). (101) is a transistor, which is expensive and high quality.
For example, if the transistor is for large current (10
1) is connected in series between a power source (100) and a load (104).

The transistor (101) normally operates with a small collector-emitter potential difference (voB, see FIG. 2). (201) in Fig. 2 indicates the safe operating area of the transistor (101), and s (IOMAX) indicates the maximum collector current (Io) passing through the transistor (101). (ioi
) is the maximum collector current passing through.

A diode (102) is a diode string that can tolerate a large surge current, or a diode with a large current capacity, and is connected in parallel to the transistor (101).

The diode (102) has a forward dropout voltage (Vn) that does not affect the normal operation of the transistor (101). That is, as shown in FIG. 2, the collector-emitter voltage (VoB) of the transistor (101) is set below a voltage that can be protected. In other words, when (203) current flows, (2
As the voltage shown in 02), the transistor (101)
is the driving condition within the safe operating area (201),
The forward dropout voltage of the diode (102) (
VD), the transistor (101) will not be destroyed.

(108) and (109) are resistors, which are connected in series and connected in parallel to the power supply (100).

(113) and (114) are also resistors, and are connected in series and in parallel to the load (104).

(111) is a differential amplifier, and resistors (108, 109)
The input voltage obtained from the connection point of and the resistor (113, 1
14) and the output voltage obtained from the connection point is amplified and output. Note that (110) is a capacitor, which is connected in parallel with the resistor (109).

(103) is a resistor for current detection, and resistor (109)
and (114), the resistor (103)
A minute voltage, that is, a voltage corresponding to the collector current (Io) flowing through the transistor (101) is generated at both ends of the transistor (101).

(105) is the second differential amplifier, and the detection resistor (10
3) Amplify by inputting a minute voltage from both ends. (107
) is a reference voltage, and the comparator (106) is connected to the reference voltage (10
7) and the output of the differential amplifier (105), and when the output of the differential amplifier (105) exceeds the reference voltage (107), a cutoff signal (Sl) is output.

(112) is an addition and driving circuit that adds the output of the first differential amplifier (111) and the cutoff signal (Sl) that is the output of the comparator (106), and sends the signal to the transistor (101). A driving signal (S2) is given. In other words, if there is a cutoff signal (Sl) from the comparator (106), the operation of the transistor (101) is cut off and the cutoff signal (Sl
), the transistor (101) would operate and absorb the ripple voltage contained in the output of the power supply (100).

In the above-described embodiment, when the power supply is turned on or when there is an overcurrent, an excessive current flows through the diode 102'i instead of the transistor 101. This protects the transistor 101. Note that generally the diode 102
Before the overcurrent passing through exceeds the allowable current value of the diode itself, a fuse or breaker included in the power supply 100 or an overcurrent protection circuit is activated. As described above, the expensive large current transistor 101 can be easily protected.

Note that the diode 102 only needs to have a forward voltage of a predetermined value, and it goes without saying that not only a normal diode but also a Zener diode or the like can be used.

Further, 103 and 10 forming the current detection circuit (103a)
hFB of transistor 101 even without 5°106 etc.
Using the property that the forward current increase rate depends on the collector current, the base current value of the transistor is limited to a certain value or less in advance, and when the collector current exceeding the certain value flows, the collector current increases. The collector current bypassing the diode due to the large potential difference between the emitters is also considered to be a collector current protection circuit in a broad sense. Further, in the embodiment, the transistor 101 is cut off, but it is of course easy to limit the current passing through the transistor 101 and route the remaining current through the transistor 102.

As explained above, the present invention can reliably protect expensive, high-quality, high-current transistors.
It is extremely effective in practice.

[Brief explanation of the drawing]

FIG. 1 is an electronic circuit diagram showing one embodiment of the present invention, and FIG. 2 is a graph diagram explaining operating conditions of a transistor. 100: power supply, 101:) transistor, 102
: Diode (moving side bypass means, 103a: Current detection circuit, 111: First differential amplifier, 112: Addition and driving circuit. Agent: Patent attorney

Claims (1)

[Claims] In a circuit having a transistor connected in series with a power supply, when a certain voltage corresponding to a desired allowable current of the transistor is exceeded, bypass means is connected to the transistor to bypass the current flowing through the transistor. A protection circuit for a transistor, characterized in that it protects the transistor.