JPS6130957A - Drive device of semiconductor switch - Google Patents

Abstract

PURPOSE:To reduce power consumption of a reverse bias power source by containing a time limiting timer for reverse bias, and connecting a reverse bias voltage applying circuit in parallel with a switching element for a reverse bias current, thereby preventing a shortcircuit defect. CONSTITUTION:A forward bias unit 20 for driving a semiconductor switch 40 is formed of a forward bias power source 21, a forward bias transistor (Tr)22, and a resistor 23, and a reverse bias unit 70 is formed of a reverse bias power source 71, a reverse bias FET72, an inverter 73, a time limiting timer 47, an auxiliary reverse bias FET75, and a resistor 76. The forward and reverse bias currents from the units 20, 70 are flowed to the base of the switch 40 to turn ON and OFF the collector current Ic. Thus, when an OFF command signal is inputted to a signal input terminal 10, the Tr22 is immediately turned OFF, reverse bias FETs 72, 75 are further turned ON through the inverter 73 and the timer 74 to reversely bias the setting time T74 of the timer 74.

Description

[Detailed Description of the Invention] [Technical field to which the invention pertains] The invention of r is a half-1-off switch. The present invention relates to a drive device for a control electrode that performs continuous operation.

[Prior art and its problems]

The prior art and its problems will be explained below, taking as an example a case where a transistor is used as a semiconductor switch.

FIG. 3 is a circuit diagram showing a conventional example of a transistor base driving device. In this FIG. 3, symbol input terminal 10
A signal with a waveform A in which ON commands and OFF commands are alternately received is input to . The forward bias device is composed of a forward bias power supply 21, a forward bias transistor n, and a resistor, and the reverse bias device is composed of a reverse bias power supply 31 and a reverse bias field effect transistor (hereinafter, a reverse bias F).
(abbreviated as ET) 32 and an inverting element 33, and when an on command signal is input to the signal input terminal IO, the forward bias transistor n is turned on via the resistor n, so that the forward bias voltage from the forward bias power supply 21 is turned on via the resistor n. A forward bias current flows between the base and emitter of the main transistor 40 as a semiconductor switch, turning the main transistor 40 on. When the main transistor turns on for the first time, a current Ic flows from the main power supply ω to the load 50.

Next, when the signal input to the signal input terminal 10 changes from the on command to the off command, the forward bias transistor n turns off, and at the same time, the off command signal turns on the reverse bias FET 32 via the inverting element a, so the main transistor 40 A reverse bias current supplied from the reverse bias power supply 31 flows in the direction from the emitter to the base, and this main transistor 40
Turn off immediately. Note that 41 is an internal resistance between the base and emitter of the main transistor 40, and 1
B is the base current of the main transistor 40, Ic is the collector current of the main transistor, and VBE is the main transistor 4
This is the voltage that appears between the base and emitter of 0.

FIG. 4 is an operational waveform diagram of each part of the conventional circuit shown in FIG. 3, and FIG. 4 (a) shows the waveform of the on/off command signal A;
FIG. 4(b) shows the collector current Ic of the main transistor 40.
FIG. 4(c) is the waveform of the base voltage iIa of the main transistor 40, and FIG. As can be seen from the figure, when turning the main transistor 40 from on to off, a large reverse bias current must be applied to the base I, and the turn-off time is indicated by TI.

The conventional circuit shown in FIG. 3 has the following drawbacks. In other words, the entire time during which a large reverse bias current flows through the reverse bias FET 32i (the ratio of
z, 5% assuming a turn-off time of 5 microseconds). On the other hand, the reverse bias FET 32 is capable of passing a large peak N current for a short time, but cannot be passed continuously, so if damage occurs such as a short circuit between the base and emitter of the main transistor 40, In this case, a large reverse bias current continues to flow through the reverse bias FET 32, which may not only burn out the reverse bias FET 32 but also damage the reverse/XI bias power supply 31.

Furthermore, if the reverse bias current is limited by a current limiting resistor or the like to prevent burnout even if the reverse noisy current is continuously applied to the reverse bias FET 32, the loss in the current limiting resistor will not only increase, but the main transistor 40 will Since the turn-off time T1 becomes longer, high-speed switching operation cannot be performed. Furthermore, there is an internal resistor 41 between the base and emitter of the main transistor 40 to improve breakdown voltage and prevent erroneous turn-on, and for this reason, when the main transistor 40 is turned off and is reverse biased, power from the reverse bias power supply 31 is removed. occupies a large proportion of the power consumption when turning off the main transistor 40.

[Purpose of the invention]

This invention prevents the reverse bias device from being damaged even if the control electrode of the semiconductor switch is damaged such as short-circuiting, and reduces the power consumption of the reverse bias power supply in the off state after the semiconductor switch is turned off. An object of the present invention is to provide a driving device for a semiconductor switch.

[Key points of the invention]

This invention operates a switching element so that a large reverse bias current flows for a time sufficient to turn off the reverse bias device of a semiconductor switch, and also prevents erroneous on operation when the semiconductor switch is in the off state. By connecting a circuit that applies a moderately small reverse bias pressure in parallel to the switching element, the time required for a large reverse bias current to flow in the event of damage such as a short circuit of the semiconductor switch control electrode can be reduced. This aims to significantly reduce the power consumption of the reverse irradiation source in the OFF state.

(Embodiment of the Invention) FIG. 1 is a circuit diagram showing an embodiment of the present invention, and shows the case of a semiconductor switch crab transistor, similar to the conventional example shown in FIG.

In FIG. 1, reference numeral 10 denotes a signal input terminal, into which a signal waveform A in which ON commands and OFF commands are alternately received is input. The sign addition is a forward/< ias device, which is composed of a forward bias power supply 21, a forward bias transistor n, and a resistor n, and the reverse/XI ias mounting 70 is a reverse bias power supply 71 and a reverse bias FET as a switching element.
72, inverting element 73, time limit timer 74, auxiliary reverse bias FET 75 as an auxiliary switching element, and resistor 76
It is made up of. The forward bias current from these forward bias devices or the reverse bias current from the reverse bias device 70 is applied to the main transistor 40 as a semiconductor switch.
By flowing into the base of the main transistor 40 as a base current IB, the collector current IC of the main transistor 40 is turned on and off. Note that 41 is the internal resistance between the base and Q-emitter of the main transistor 40, VBE is the voltage that appears between this base and E-emitter, and 50 is the load, and ω
is the main power supply.

When the ON command signal is input to the signal input terminal 10, the forward bias device operates and causes a forward bias current to flow through the main transistor 40 to turn on the main transistor 40, so that the load 50 receives power from the main power source ω. Electric power is supplied in the same manner as in the conventional example shown in FIG.

When the off command signal is input to the signal input terminal 10, the forward bias transistor η is immediately turned off, and the forward bias current flowing to the base of the main transistor 40 is cut off. The reverse bias FET is inverted by the inverting element 73 and the reverse bias FET is
72 is turned on, but one auxiliary reverse bias FET is turned on at the same time.
Turn on 75 as well. Therefore, the main transistor 40 has a first route of reverse bias power supply 71 → emitter of the main transistor → base of the main transistor → reverse bias FET 72 → reverse bias power supply 71 → emitter of the main transistor → main transistor Reverse bias 1! by the second route: base → resistor 76 → auxiliary reverse/sl Ias FET 75 → reverse bias power supply 71! Current flows and turns off the main transistor 40, but since the resistor 76 is inserted in the second route, the current flowing through this second route is small, and the turn-off operation of the main transistor 40 is mainly caused by the This is due to the effect of the reverse bias current flowing through the first route. But lever 0)
The energization time of the reverse bias current flowing through the first route is limited to only the time T74 set by the J time limit timer 74.

Since the turn-off time T1 of the main transistor 40 varies depending on the junction temperature of the main transistor 40 and the collector current Ic immediately before turn-off, the current limit timer 74
The set time T74 is set to be sufficiently longer than the expected maximum turn-off time to ensure that the main transistor 40 is turned off, and to prevent an accident such as a short circuit between the base and emitter of the main transistor 40. Even if this occurs, the reverse bias FET 72 is automatically turned off after the set time T74 has elapsed, and only a small amount of reverse bias current flows through the aforementioned second route, thereby preventing the reverse bias device 70 from burning out.

Even if the main transistor 40 is turned off by the off command signal and the reverse bias FET 72 is turned off after a time period of Tta has elapsed, the series connection circuit of the auxiliary reverse bias FET 75 and the resistor 76 that is in the on state remains the aforementioned reverse bias FET 7.
2, a slight reverse bias voltage is applied between the base and emitter of the main transistor 40 to prevent the main transistor 40 from turning on accidentally. Since the resistance value of the resistor 76 may be about 10 times the resistance value of the internal resistor 41 of the main transistor 40,
This means that the power consumption G of the reverse bias power supply 71 when the main transistor 40 is in the OFF state is very small.

FIG. 2 is an operational waveform diagram of the circuit of the embodiment shown in FIG. 1, and FIG.
Figure to) is the waveform of the collector current 1c of the main transistor 40, and Figure 2 (c) is the waveform of the base current I of the main transistor 40.
The waveform B (in FIG. 2) is the waveform of the voltage VBH that is applied between the main I and the base ψ emitter of the transistor 40, and FIG. . Further, T1 is the main transistor. [Effect of the Invention] According to the present invention, a time limit timer is provided in the reverse bias device for turning off the semiconductor switch to cause the IA current to flow in reverse for a sufficient time to turn off the semiconductor switch. By incorporating a circuit that applies a low reverse bias voltage that can prevent the semiconductor switch from turning on accidentally and connecting it in parallel to the reverse bias current switching element, accidents such as short-circuiting of the control electrode of the semiconductor switch can be avoided. Even if the reverse bias device is turned off, there is no risk of burning out the reverse bias device, and furthermore, this semiconductor switch will not be accidentally turned on, and the power consumption of the reverse bias power supply when turned off can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is an operational waveform diagram in the circuit of the embodiment shown in FIG. FIG. 3 is a circuit diagram showing a conventional example of a transistor base driving device, and FIG. 4 is an operating waveform diagram in the conventional example circuit shown in FIG. 10...Signal input terminal, addition...1 bias device, addition...reverse bias device, 31...reverse bias power supply, 32
... Reverse bias FET%... Inversion element, 40...
Main transistor as a semiconductor switch, 41... Internal resistance between base and emitter of main transistor, 50...
・Load, ω...Main power supply, 70...Reverse bias device,
71... Reverse bias power supply, 72... Reverse bias FET as a switching element. 73... Inversion element, 74... Time limit timer, 75...
Auxiliary reverse bias FET as an auxiliary switching element,
76...Resident Patent Attorney Yamaguchi Ishi Figure 1 Figure 2

Claims (1)

[Claims] In a semiconductor switch driving device that turns off a semiconductor switch by flowing a reverse bias current in response to an off command given to a conductive semiconductor switch, the semiconductor switch is reverse biased for a period sufficient to turn off the semiconductor switch along with the off command. a reverse bias circuit composed of a switching element that allows current to flow and a timer that controls the operating time of the switching element; and a reverse bias circuit that is connected in parallel to the reverse bias circuit to prevent the semiconductor switch from being turned on by mistake while an off command is being issued. 1. A driving device for a semiconductor switch, comprising: an auxiliary reverse bias circuit comprising an auxiliary switching element that applies a relatively low reverse bias voltage and a limiting resistor.