JPS60255055A - Drive circuit for semiconductor switch - Google Patents

Abstract

PURPOSE:To erroneously operator for an incoming surge voltage by connecting a capacitor with the base of a buffer transistor inserted between a thyristor and a constant-current circuit. CONSTITUTION:A drive circuit of a thyristor 23 has a buffer transistor 21, a capacitor 22 for grounding its base, a base potential generation source 24 for securing the base potential of the transistor 21, and a drive constant-current source 26 connected with the emitter of the transistor 21. When a surge voltage which falls in negative direction is applied to the case of the thyristor 23, a displacing current flowed to a capacity between the base and the collector of the transistor 21 mainly flows to the capacitor 22 by sufficiently increasing the capacity of the capacitor 22. Thus, mirror effect does not occur in the base current of the transistor 21.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a semiconductor switch drive circuit, and particularly relates to a semiconductor switch drive circuit consisting of a semiconductor switch using a thyristor and a constant current circuit. For example, the drive circuit is based on Japanese Patent Application Laid-Open No. 5
3-4458, etc. FIG. 1 is a circuit diagram showing an example of a conventional semiconductor switch drive circuit. In the figure, an on-drive circuit 14 drives a semiconductor switch using a thyristor 11. When a switch 15 is turned on, the collector current of the transistor 12 is transferred to the thyristor 11.
The current flows into the P gate of No. 1 and turns the thyristor 11t on. On the other hand, when the switch 15 is off, the P gate current does not flow and the thyristor 11 remains off.
Considering the case where a surge voltage 16 falling in the negative direction is applied to the cathode of the thyristor 110 in this state, the base-collector capacitance of the transistor 12 (hereinafter referred to as CJo) 1
3t - a displacement current flows through the transistor 12
Since it becomes 0 pace current, CJO13 due to the Miller effect
appears to be larger than the h parameter hFE of the transistor 12, and the h parameter hFB s CJ
Depending on the size of O, sufficient current may flow from the P gate to turn on the thyristor 11, causing a malfunction? (Objective of the Invention) The object of the present invention is to eliminate all of the above drawbacks by reducing the gate current due to the equivalent capacitance of the drive circuit, and to provide a stable semiconductor switch drive circuit free from malfunctions. It's about doing.

(Structure of the Invention) According to the present invention, in a semiconductor switch drive circuit including a semiconductor switch using a thyristor and a constant current circuit, a buffer transistor inserted between the thyristor and the constant current circuit, and a base of the buffer transistor are provided. A semiconductor switch drive circuit is obtained which is characterized by a capacitor connected to the capacitor.

(Example) Next, the present invention will be described with reference to all of FIGS. 2 to 5.

2, 3, 4 and 5 respectively show the first, second and second stages of the semiconductor switch drive circuit according to the present invention. Third and Fourth Embodiments In FIG. 2, the first embodiment includes a buffer transistor 21, a capacitor 22 whose base is grounded, a thyristor 23, and a base potential of the buffer transistor 9, the base potential generation source 24 actually has a finite internal resistance r'2. However, the buffer transistor 21 has a CJO25t-. When a surge voltage (not shown) falling in the negative direction is applied to the cathode of the thyristor 23, the CJO 25' of the buffer transistor 21 (
By making the capacitor 22 sufficiently large, the displacement current that flows mainly flows through the entire capacitor 22, so that it does not become the base current of the buffer transistor 21 and the Miller effect does not occur.

Therefore, the equivalent capacitance of this circuit is the buffer transistor 21
The CJO is about 25, which is E compared to the capacitance when transistors of the same size as the on-drive circuit are provided all around.

Next, in FIG. 3, the second embodiment has an N gate and a P gate.
A thyristor 33 having both gates, two buffer transistors 31.35 having a common base, driving constant current sources 34.36 connected to the emitters of the buffer transistors 31.35, and buffer transistors 31.35. A capacitor 32 and a base potential generation source 37'vl- are commonly connected to the base of the . It is clear that in the second embodiment, the total equivalent capacity of the drive circuit can be reduced not only for the negative surge voltage applied to the cathode of the thyristor 33, but also for the positive surge voltage applied to the anode. Next, in FIG. 4, the third embodiment includes two thyristors 43, 45,
It includes a capacitor 42 and a pace potential generation source 48 which are commonly connected to the bases of buffer transistors 41 and 440, and the thyristors 43 and 45 each have a constant current source 47 and 4 for driving through the buffer transistors 41 and 44, respectively.
6 is connected. According to the third embodiment, two or more semiconductor switches are also capacitors.

The same effect as the first embodiment can be obtained without increasing the pace potential generation source. Next, in FIG.
, a buffer transistor 51 inserted only on the ON drive circuit 54 side, and a capacitor 5 connected to its base.
According to a fourth embodiment comprising two thyristors 5
When a negative surge voltage is applied to the cathode of transistor 5, the displacement current becomes large on the off drive circuit 55 side, and
6 is turned on, it is possible to prevent the thyristor 53 from transitioning to the on state.O (Effects of the Invention) As explained above, the semiconductor switch drive circuit of the present invention is a buffer transistor in which the entire capacitance is inserted in the base. By inserting the thyristor between the thyristor gate and the f drive circuit, there is the effect of providing stability that prevents malfunctions against external surge voltages.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional semiconductor switch drive circuit, and FIGS. Second.
FIG. 6 is a circuit diagram showing third and fourth embodiments. In the figure, 11. 23. 33. 43. 45゜53...Thyristor, 14,5.4...On drive circuit, 21.31,35,41,44.51...Buffer transistor, 22,32,42.52...Capacitor, 24 ．． 37. 48...Base potential generation source,
25... Inter-pace collector capacity, 26. 34. 3
6,46°47... Constant current source for drive, 55... Off drive circuit, 56... Transistor for off drive. Line 2, line 3, foil illustration

Claims (1)

[Claims] In a semiconductor switch drive circuit including a semiconductor switch using a thyristor and a constant current circuit, a buffer transistor inserted between the thyristor and the constant current circuit;
A semiconductor switch drive circuit 0 characterized in that it comprises a capacitor connected to the base of the buffer transistor.