JPS60141013A - Base drive system of switching transistor - Google Patents

Abstract

PURPOSE:To decrease loss by connecting a semiconductor switching element between the collector and base of a switching transistor (Tr) so as to decrease the transient loss at turn-on period thereby constituting single Tr at the normal on-period. CONSTITUTION:A TrT1 is used as a switching element. In flowing a base drive current iB1 of the TrT1 at a point (a) in Fig., the T1 is conducted, its collector current ic1 flows and a drive current iB1 so that the ic1 is several times the iB2 in this case, the turn-on loss is decreased. Then a reverse base current flows to the TrT1 at a point of time (b) when a voltage VCE of the TrT2 goes to a steady-state value. The base current of the TrT2 at this point of time is expressed as iB3=iB2, the TrT1 is turned off, the TrT2 is constituted singly, the VCE of the T2 is smaller sufficiently in comparison with the Darlington connection and the loss at the steady-state on-state is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to a base drive system for a single power transistor that performs a switching operation.

[Prior art and its problems]

Single power transistors have a smaller LIFE (large signal current transmission rate with common emitter) than Darlington-connected transistors, and as shown in Figure 11, especially when turned on, the base current IB necessary for the normal on state is supplied. Immediately after turn-on, however, a transiently large collector-emitter voltage VCE is generated, resulting in a large turn-off loss P. - In order to solve this drawback, the following two methods have been conventionally used.

One of them is to apply an overdrive current to the base of the transistor. Figure 2 shows the waveforms of each part when overdrive current is applied in this way.
Transient collector emitter voltage VC immediately after turn-on
It can be seen that E is smaller than in FIG. 1, and therefore the error generated by the collector is also smaller.

However, this method has the disadvantage that when the switching transistor is a single transistor, hrE is small, the necessary overdrive current is sometimes comparable to the collector current, and the base drive circuit becomes very large.

Another method is to connect another transistor T, Darlington to the switching transistor T2, as shown in FIG. With such a configuration, as is well known, the normally used base drive current lB1 is 11 FE of transistors T1 and T2, hFE, ,
If it is hFc2, then c B1- hFE, -1 heat IF E2 + h FE, ・hFE2
As IB, only a small current is required.

Also, considering the turn-on transient state, transistor T1 is turned on first, and then transistor T2 is turned on.
turns on, sufficient current flows through IB2 until T2 turns on. This is equivalent to flowing an overdrive current, and similarly to the case of flowing an overdrive current described above, turn-on can be achieved quickly and turn-on loss can be reduced.

However, as is well known, the collector-emitter voltage VCE2 of the switching transistor T2 when connected to Darlington is VCE2 = VBE + VCE, and the on-voltage VCE is higher than when it is normally used as a single. Therefore, there is a drawback that the collector loss in the steady on state becomes large.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned disadvantages, and to provide a base drive method for a switching transistor that has a simple configuration that efficiently reduces turn-on loss without using a large base drive circuit, and does not increase on-loss in a steady state. Our goal is to provide the following.

[Key points of the invention]

According to the present invention, this purpose is to connect a semiconductor switching element between the collector base of a switching transistor, turn on the switching element during the turn-on period of the transistor, reduce transient loss, and reduce transient loss during the steady-state/on period after turn-on. This is achieved by turning off the switching element and using a single transistor to reduce the loss during the steady on period.

[Embodiments of the invention]

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

FIG. 4 shows the principle of the method of the present invention, in which a switching element S is connected between the collector and base of the main transistor T2, which is a driven transistor, and the switching element S1 is turned on only when the main transistor T2 is turned on. In the subsequent steady-on period, the switching element S,
I turned it on. In the figure, BD is a base drive circuit connected between the base and emitter of the main transistor T2.

FIGS. 5 and 5 are circuit diagrams showing the first embodiment of the present invention;
A transistor T is used as a switching element S1.

was used. This front stage transistor T1 is turned on only when the main transistor T2 is turned on, and is driven by the base drive circuit BD.

Next, FIG. 6 shows the current and voltage waveforms of each part. When the base driving current 1131 of the transistor T is passed at the 0 point,
T, becomes conductive and current lC1 flows through its collector. At this time, at the same time, a current lB2 necessary for the normally on state of the main transistor T2 is caused to flow from the base drive circuit BD. The base of the main transistor T2 has i B3=ic, +i
A current of B, , flows, but if IB is selected so that the value of lC4 is several times the value of IB2, a base drive current several times the normal value will flow through T2, Turn-on loss can be reduced.

Next, the collector-emitter voltage yc of the main transistor T2
At the point (2) when g almost reaches a steady value, a reverse pace current is applied to the main transistor T1, and the transistor T is turned off. At this point, the base current of the main transistor T2 is iBs = i B2.Since the transistor T is off, the main transistor T2 has a single configuration.The VCE of T2 is VC when connected to Darlington.
As a result, the loss in the steady on state is extremely small compared to the case of Darlington connection.

Note that 1B2 may be made to flow independently at the 0 point instead of flowing at the 0 point at the same time as in.

FIG. 7 is a circuit diagram showing a second embodiment of the present invention, in which an FET (field effect transistor) is used as the switching element S in place of the bipolar transistor T1.

If a normal bipolar transistor is used in the front stage of the Darlington, it takes time to turn off and the overdrive period becomes longer, resulting in increased base loss when operating at high frequencies. - If you try to flow a large reverse bias current to the front transistor in order to shorten the turn-off time, the base drive device BD of the front transistor
becomes larger.

In such a case, a field effect transistor FETI can be used to quickly turn off the previous switch as shown in FIG. Furthermore, as another example, as shown in FIG.
The field effect transistor FET and the bipolar transistor T1 may be connected in U columns.

In general, field-effect transistors (FETs) do not have high voltage and large current compared to bipolar transistors, so it may not be possible to directly configure them with only FETs. Can be configured as a front-stage switch for switching (quick turn-off).

That is, when transistor T2 is off, F is always
ET] is turned on so that the full voltage is applied to 1-transistor T.

At the time of turn-off, the FET is turned off in a very short turn-off time, and at this time no collector current flows through T1, so the FETs can be turned off almost simultaneously.

As shown in FIG. 9, a gate turn-off thyristor GTO1 may be used as the switching element S1, and SL, T (static induction type zyristor or static induction type transistor) may be used for the part 9 of this GTOI. It is also possible to do so. In any case of these figures 7 to 9,
A gate drive circuit GD is provided, and the gate drive circuit GD and the base drive circuit BD may have any configuration.

〔Effect of the invention〕

As described above, the base drive method of the switching transistor of the present invention turns on the previous switch only during turn-on to create a Darlington configuration, and turns off the switch during the steady on period to create a single configuration, thereby driving a large base. The loss during the turn-on period can be efficiently reduced with a simple circuit configuration without using any circuit, and the loss during the steady-on period does not need to be increased.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram of each part of the transistor when base 1 of the switching transistor is driven and the base current is not overdriven. Figure 2 is a waveform diagram of each part of the transistor when the base current is not overdriven. Figure 3 is a circuit diagram showing a conventional base drive circuit;
The figures are explanatory diagrams showing the principle of the method of the present invention, Fig. 5, Fig. 7,
8 and 9 are circuit diagrams showing embodiments of the present invention, respectively, and FIG. 6 is a waveform diagram showing the operation of each part of the circuit of FIG. 5. T4, T2 ・Transistor, SL ・・Switching element, FET] ・・Field effect transistor, GTOl −
Gate turn-off circuit, BD: base drive circuit, GD: gate drive circuit. Applicant: Fuji Electric Manufacturing Co., Ltd. Figure 1 A'-Jindenshin is □ Figure 2 CE Collector visit 1 day (□ Figure 5 Figure 4 Figure 6! B1: b Figure 7 Figure 8

Claims (1)

[Claims] A semiconductor switching element is connected between the collector base of the switching transistor, the switching element is turned on during the turn-on period of the transistor to reduce transient loss, and the switching element is turned off during the steady-on period after turn-on to turn off the transistor. A base drive method for a switching transistor characterized by having a single configuration and being able to reduce 1μ loss during a steady on period.