JPS6130916A - transistor circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention particularly relates to a short-circuit protection device for a transistor circuit using a transistor as a main switching element.

[Background of the invention]

FIG. 1 shows a known inverter using transistors as main switching elements. Considering the case where one of the transistors T, -T6 constituting the inverter 4 in this circuit, for example T, has a short-circuit failure, the following will occur.

As shown in Figure 2, the current in the transistor T increases to the level that indicates a short-circuit failure, and continues to flow. If the detection means 8 and the control means 7 are set to 0, the cutoff starts after the operation delay ta of the detection means 8 and the control means 7, that is, at time T, and then at time T.

Shutdown ends.

However, the switching element T was cut off at this time.

will consume the following energy A.

A=VceXIcXTw (J) Vce: Voltage between collector and emitter (here, Vce〒
Inverter 40 input voltage Vc) Tw: Short circuit time 70~T.

The energy A in the above equation is the amount of heat that increases the temperature of the transistor, for example, a silicon chip, and if it exceeds the withstand capacity of the transistor, it will be destroyed.

In other words, if one transistor fails due to a short circuit, the paired element will be destroyed secondary to the ON signal. In this case, even if an abnormal current is detected during a short circuit, it cannot be safely cut off and the equipment cannot be stopped.

The following measures can be taken in order to avoid this kind of busyness, but this will cause additional problems.Vce should be used within a certain value.

Problems: (a) The device cannot be used for receiving high voltages.

(b) During regenerative braking, it is necessary to clamp the smoothing capacitor 30 so that the voltage and voltage across it do not increase too much. 02. Use the IC within a certain value. (Supply the base current within a certain value. Or use one within a certain value of Hfθ.) Problem: During overload operation, the base current is insufficient and Vce cannot be used in the saturation region, resulting in ON loss. There is a risk of increase and destruction.

3. Use Tw within a very short period of time.

Problem: (a) Below about 50 μθ, there is almost no increase in withstand capacity even within this range. Considering the prevention of malfunction of the current detection means 8 and control means 7, it is desirable that the operation delay time be longer.

etc.

Note that an overcurrent protection circuit for a circuit using a transistor as a main switching element is disclosed in Japanese Patent Application Laid-Open No. 49-51529.
is publicly known.

Further, as shown in FIG. 3, gates and turn-off thyristors G, to G are used as main switching elements.

, a parallel circuit of the current limiting reactor 12 and the flywheel rectifying element 15 is connected in series with the main switching element, and a series circuit of the parallel circuit and the gate turn-off thyristors 01 to G6 is connected. is connected in parallel to the smoothing capacitor 5.For example, the force ζ is ``
Hitachi Review” v0163, Muro “Application of GTO Cyrisk to PWM inverter for AC motor 1” is introduced in Figure 9.

According to this K, as shown in FIG. 4, when a short circuit occurs at time T0, the short final current 1c gradually increases.

Then, if the overcurrent detection level is set to t, the operation delay of the detection means 8 and the control means 7 is delayed T (after 1, that is, at time T
1, and then ends at time T1.

However, in the case of a gate turn-off thyristor, the maximum value dm of the interrupting current must be less than the controllable current, so if the short circuit current IC exceeds the maximum value dm, the current limiting reactor 1
Even if 2 is provided, it cannot be interrupted and the overcurrent will cause damage.

In other words, when using a gate turn-off thyristor as the main switching element, providing a parallel circuit of the current-limiting reactor and the flywheel rectifying element has the effect of suppressing the rapid rise of short-circuit current. It does not work to increase the control current value.

[Purpose of the invention]

An object of the present invention is to provide a transistor circuit in which the controllable current of the transistor can be increased in a circuit using a transistor as a main switching element.

[Summary of the invention]

In the present invention, in a device using a transistor as a main switching element, a parallel circuit of a current limiting reactor and a flywheel rectifying element is connected in series with the main switching circuit, and the parallel circuit and the main switching circuit are connected in series. Connect the series circuit with the smoothing capacitor in parallel.

By configuring as described above, the short-circuit tolerance of the transistor as a main switching element is increased.

[Embodiments of the invention]

FIG. 5 shows an example in which the present invention is implemented in an inverter for controlling an AC motor.

This example will be explained below.

The alternating current voltage of the power supply 1 is converted into direct current by a rectifier 2 and smoothed by a smoothing capacitor 3.

The DC voltage smoothed by the smoothing capacitor 3 is passed through the transistors T, ~T6 as main switching elements, and the flywheel diode d connected in antiparallel to the transistors T6.
The AC power is inversely converted into AC power by an inverter 4 configured as 1 to d6 and supplied to the Marugame motive 5.

This AC power is controlled by the control means described below.

That is, when a command is given by the speed command signal generating means 6, the control means 7 gives a corresponding pace signal to the transistors T1 to T6, and drives each transistor.

While the apparatus is in operation, the input current to the reverse side is constantly detected by the DC current transformer 8 as a detection means. This detection signal is used by the control means 7 as a feedback signal, and when the detected current value exceeds a certain value, the control means 7 is operated to eliminate the pace signal to the transistors T, -T0.

A parallel circuit of a current limiting reactor 12 and a flywheel rectifying element 13 is connected in series to the inverter 4,
Further, a series circuit consisting of this parallel circuit and an inverse conversion circuit is connected in parallel to the smoothing capacitor 3.

The short-circuit current cutoff when the switching element T1 causes a short-circuit failure will be explained using the above circuit.

As shown in FIG. 6, the short-circuit current IC begins to flow and increase at time T(1).The input voltage Vc of the inverter is short-circuited by the switching elements T, and T, so that Vco.

becomes. On the contrary, the voltage 8 across the actuator 120 becomes e : V da (V (voltage across the 1 cm smoothing capacitor 3)) due to the voltage drop. After that, the short circuit current If increases at an increasing rate of 111c Vda dt IL . If the overcurrent detection level at this time is set to tK, the cutoff starts after an operation delay Td of the detection means 8 and the control means 7, that is, at time T1, and ends at time T.

Note that from time point T, the input voltage Vc of the inverter starts to gradually increase. This is because the pace current jb becomes insufficient as the short circuit current IC increases, and the collector of the switching element T,
This is because the emitter voltage Vcθ has increased. Also, the rate of increase in short circuit current IC is gradually decreasing. The above operation reveals the following.

1, T, -T, the reactor 12 bears most of the short-circuit energy. In other words, the energy A borne by the current limiting reactor 12
12 is A, ,=i:VceXICXTw (Vce-FVdc
), and on the other hand, the energy A, borne by the transistor T, is A, =i=VceXICxTw (Vcei, 0)
It is.

・°・A,,)A.

2, T, -T, the share of the short-circuit energy is being transferred from the current limiting reactor 12 to the switching element T, but the energy consumption of the switching element T during this period is small compared to that in FIG.

Assuming that the energy consumption when a switching element is short-circuited is limited to a certain value from the above, the formula 仝 vo vo. =-people-CXTw. Here, Tw= is assumed to be a fixed constant of 1. (Since it is a very short time, it does not directly affect the withstand capability.) Also, if Td is considered to be fixed, Vce can be increased by making the IC smaller. In other words, even if the DC circuit voltage Vdc is considerably high, the transistors T1 to T6 will not be destroyed, so the short-circuit resistance can be increased.

In the above embodiments, a case has been described in which an inverter is used as the main switching circuit, but it is also possible to use a chopper composed of transistors instead of the inverter.

〔Effect of the invention〕

According to the great invention, the rate of increase in short-circuit current or abnormal current can be determined by the reactor, resulting in the following effects.

1. The short-circuit resistance of the transistor can be increased.

2. It is not necessary to reduce the base current in order to increase the short-circuit resistance compared to the base current required during operation such as 2."-11i14-1.

3. The rate of increase in short circuit or abnormal current can be determined by the accelerator and is not affected by the base current.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional transistor inverter.
Figure 2- is a time chart for short circuit in Figure 1, Figure 3 is a block diagram of an inverter using a conventional gate turn-off thyristor, Figure 4 is a time chart for short circuit in Figure 3, and Figure 5 is a time chart for short circuit in Figure 1. FIG. 6 is a block diagram showing an embodiment of the transistor circuit of the present invention, and is a time chart when the circuit shown in FIG. 5 is short-circuited. 3 is a smoothing capacitor, T, ~T6 are transistors, d,
-d are flywheel elements, 4 is a reverse converter, 7 is a control means, 8 is a detection means, 12 is a current limiting reactor, and 13 is a rectifier for the flywheel. $10 20 Figure 3 Figure 4

Claims (1)

[Claims] 1. A main switching circuit having a flywheel element whose main switching element is a transistor, a smoothing capacitor connected to the input side of the main switching circuit, and detecting the input current of the main switching circuit. and a control means that receives a signal from the detection means and eliminates the base signal to the transistor when the signal indicates that the input current is greater than or equal to a predetermined value. A parallel circuit of a current limiting reactor and a flywheel rectifying element is connected in series with the main switching circuit, and a series circuit of the parallel circuit and the main switching circuit is connected in parallel with the smoothing capacitor. A transistor circuit characterized by being connected. 2. The transistor circuit according to claim 1, wherein the main switching circuit is an inverter. 3. The transistor circuit according to claim 1, wherein the main switching circuit is a chopper.