JPS63316919A - Snubber circuit for switching semiconductor device - Google Patents

Abstract

PURPOSE:To lower the price of a snubber circuit by reducing the reverse bias safety operation area of a main transistor, by providing a parallel circuit with a first diode, and providing a second diode at least with the same polarity as that of the first diode and whose recovery time in a forward direction is smaller than that of the first diode. CONSTITUTION:A snubber diode equivalence circuit DSI is constituted of the parallel circuit of a fast switching diode D2 whose recovery time in the forward direction is slow and whose recovery time in a backward direction is fast used in an on-going device, and an ordinary diode D1 whose recovery time in the forward direction is fast and whose recovery time in the backward direction is slow. As the ordinary diode D1, a diode smaller in capacity than that of the fast switching diode D2 is selected. In such a way, when the main transistor Q1 starts to be turned off, a collector current Ic starts shunt to a snubber capacity Cs side at a fast rise speed via the D1 in the snubber diode equivalence circuit DSI. Thereby, a first spike voltage VP1: is decreased. Since the ordinary diode D1 is the one small in capacity and whose voltage drop VF in the forward direction is large, most of a shunt current flows on the fast switching diode D2.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a snubber circuit (surge breaker) for absorbing a spike voltage applied to a high-speed switching semiconductor device for power use, and in particular, the present invention relates to a snubber circuit (surge breaker) for absorbing a spike voltage applied to a high-speed switching semiconductor device for power, and in particular to a first spike voltage due to the slow forward recovery time of a high-speed snubber diode. This invention relates to a snubber circuit for easy reduction. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

[Conventional technology]

FIG. 4 is a circuit diagram showing an example of the main part configuration of this type of switching semiconductor device. In the figure, ■d is a DC power supply and its voltage, Ql is the main transistor for switching,
L is the load, DO is the commutation diode connected to both ends of the load, IS is the stray inductance generated in the main circuit wiring of the main transistor Q1, and Cs, Rs, and Ds are the snubber capacitors and snubber resistors that are the main components of the snubber circuit. , which is a snubber diode. The snubber diode Ds is for directing the main circuit current (collector current in this example) Ic, which is to be maintained by the floating inductance IS, to the snubber capacitor Cs when the main transistor Ql is turned off. The purpose is to suppress the application of overvoltage between the collector and emitter of the device. FIG. 5 is a waveform diagram showing changes in the collector-emitter voltage VCt of Ql and the collector current 1c of this transistor Ql when the main transistor Q1 is turned off. Two spike voltages appear in this voltage VCE, namely a first spike voltage vpl and a second spike voltage p2. Here, the second spike voltage Vp2 is V I)z = V d + I c 1 s /
Since it is shown as Cs −・−=−−−・(1), Vp
In order to lower z, the value of the snubber capacitor CsO may be increased, but the first spike voltage Vpl is a voltage generated at the beginning of the turn-off of the main transistor Q1, that is, at the time of the rise of the current in the snubber diode Ds, and It is determined by ls and the forward recovery time of the snubber diode Ds. For example, assume two diodes DI and D2 having forward characteristics shown in FIG. Note that here, V) is a forward voltage drop, and IF is a forward current. I) Assuming that l is a normal diode and D2 is a lifetime-controlled high-speed diode, the high-speed diode D2 has a reverse recovery current IR2 shown by the solid line in the diode current commutation characteristics in Figure 7. The reverse recovery time is short, and the normal diode DI has a long reverse recovery time as indicated by the broken line reverse recovery current TRI. Now, if the ordinary diode DI is applied to the circuit shown in Fig. 4, because of the long reverse recovery time, after the second spike voltage Vp2 appears as shown in Fig. 8, the collector-emitter voltage VCE will fall and oscillate. A waveform appears, which is likely to cause malfunction of the drive circuit of the main transistor Q1. Therefore, a high speed diode D2 has conventionally been used as the snubber diode Ds.

[Problems to be solved by the invention]

Figure 9 is a waveform diagram similar to Figure 5, and Figure 10 is the collector current 1 when Ql cuts off the inductive load by reverse biasing the base, emitter, and ivy of the main transistor Q1.
The changes in c and collector-emitter voltage VCEX are expressed as Ic and V
FIG. 6 is a diagram showing characteristics in which cEx is plotted on the vertical and horizontal axes, respectively, and a reverse bias safe operating area RBSOA as a safe operating area under such operating conditions. By the way, when a high-speed diode D2 with a fast reverse recovery characteristic is used as the snubber diode Ds, due to the slow forward recovery characteristic of this D2 (in general, a high-speed diode with a fast reverse recovery has a slow forward recovery, and a normal diode with a slow reverse recovery (forward recovery is fast), a high first spike voltage Vp+ as shown in Figure 9 is generated, the transistor operating point goes outside the reverse bias safe operating area RBSOA as shown in Figure 1O, and the device is destroyed. Cheap. For this reason, it has conventionally been necessary to select a device with a large reverse bias safe operating area RBSOA of the main transistor Ql, which poses a problem in that the cost of the transistor device is high. An object of the present invention is to provide a normal diode Di having the same polarity as the diode D2 in a parallel circuit of a snubber diode Ds using a high-speed diode D2, so that the first spike voltage V'l) I is low and It is an object of the present invention to provide a snubber circuit which can prevent the voltage oscillation falling phenomenon after the second spike voltage p2 appears and can reduce the reverse bias safe operation area of the main transistor.

[Means to solve the problem]

In order to achieve the above object, the snubber circuit of the present invention has the following features:
Switching semiconductor devices (main transistor Ql, etc.)
A snubber circuit for absorbing overvoltage applied to the switching semiconductor device, which is based on at least a capacitor (such as a snubber capacitor Cs) and a current flowing through the switching semiconductor device (such as a collector current 1c) when the device is turned off. A snubber circuit comprising a first diode (such as a high-speed diode D2) that guides the energy of floating interlock (ls, etc.) in series with the semiconductor device to the capacitor, and a parallel circuit is provided to the first diode,
It is assumed that this parallel circuit is provided with at least a second diode (such as a normal diode DI) which has the same polarity as the first diode and has a shorter forward recovery time than the first diode.

[For use]

The first diode is for high speed and has a short reverse recovery time, so no voltage oscillations occur after the second spike voltage Vpt, whereas the first diode has a long forward recovery time and the first spike voltage Vial
becomes large, which tends to cause voltage breakdown of the switching semiconductor device. The second diode is a normal diode with a short forward recovery time, and operates only at the initial stage when the current of the first diode rises to reduce the first spike voltage pl.

【Example】

1 to 3 are principal circuit diagrams showing different embodiments of the present invention, and correspond to FIG. 4. In FIGS. 1 to 3, DS1 is a circuit corresponding to the snubber diode D3 in FIG. 4 (referred to as a snubber diode equivalent circuit). It is meant to lead you to the side. In Figures 1 and 2, this snubber diode equivalent circuit DSL is used as a conventional high-speed diode D2 with a slow forward recovery time and a fast reverse recovery time, and a normal diode DI with a fast forward recovery time and a slow reverse recovery time. It consists of a parallel circuit with This first figure. In FIG. 2, the capacity of the ordinary diode Di is selected to be smaller than that of the high-speed diode D2. As a result, when the main transistor Ql starts to turn off, the collector current 1c changes to the snubber diode equivalent circuit DSI.
snubber capacitor C via the common diode DI in
Shunting to the s side is immediately started at a fast rising speed, thereby reducing the first spike voltage Vp+. Here, as time passes, the high-speed diode D2 becomes fully conductive, while the ordinary diode Di has a small capacity and its forward voltage drop V becomes large, so most of the shunt current flows to the high-speed diode D2. will begin to migrate. In addition, in order to do this, if necessary, for example, a general diode D
A non-inductive resistor (not shown) may be inserted in series with I. By adding a new small-capacity ordinary-like diode Di in this way, the accumulated carriers in this diode DI are small, and as a result, the reverse recovery current of Di, and therefore the reverse recovery time, is not relatively large, and the second spike voltage V9
Hereafter, the collector-emitter voltage of the main transistor Q1 is ■. vibration can be prevented from occurring. In addition, in Fig. 3, a snubber diode equivalent circuit Dsl
, a new capacitor C1 is provided in series with the normal diode D1, and a new resistor R1 is provided in parallel with the diode D1. In this figure 3, the ordinary diode D
There are no capacity constraints for 1. The capacitor C1 is used to energize the ordinary diode DI from the start of turn-off of the main transistor Q1 until the high-speed diode D2 becomes fully conductive, and thereafter cut off the energization of D1. R1 is a resistor for discharging the capacitor CI. In this circuit, at the end of turn-off of the main transistor Ql, the current flowing through the normal diode D1 has disappeared, so there is no reverse recovery current of Dl, and therefore the second spike voltage ■vC! after ρ2! No vibration occurs. In the above embodiments, Ql was explained as a transistor, but devices corresponding to this switching semiconductor element Q1 include a PNP) transistor, FET, IGBT, S
Other semiconductor elements such as CR and GTO may also be used. Further, the newly added diode DI may have a faster reverse recovery time than the conventionally used diode D2. In short, it is important that the forward recovery characteristic of the newly installed diode DI is faster than that of the conventionally used diode D2.

【Effect of the invention】

According to the present invention, a parallel circuit is provided in the snubber diode of the switching semiconductor device, and in this parallel circuit, at least the same polarity as the conventional snubber diode DS (=D2),
In addition, since the ordinary diode D1, which has a faster forward recovery characteristic than the snubber diode D2, is provided, the following effects can be obtained. ■The second spike voltage in the voltage across the switching semiconductor element at the time of turn-off ■The first spike voltage Vp without causing any voltage oscillation after pt. Therefore, the withstand voltage of this element is reduced, and this element can be made inexpensive. can be taken as a thing. (2) Since the diode D1 only needs to work during the forward recovery time of the diode D2, it can be smaller and cheaper than the diode D2, and the snubber circuit itself newly provided with the diode D1 can be constructed at a lower cost. - When designing the snubber circuit, it is only necessary to select the snubber diode D2 by paying attention to its reverse recovery characteristics, which expands the scope of selection and ultimately shortens the design time.

[Brief explanation of drawings]

1 to 3 are main part circuit diagrams as different embodiments of the present invention, FIG. 4 is a conventional main part circuit diagram corresponding to FIGS. 1 to 3, and FIGS. 5 to 10. is a characteristic diagram or a waveform diagram for explaining the operation of FIG. 4; vd: Main DC power supply, Ql: Main transistor, lS: Floating inductance, L: Load, Do: Free-wheeling diode, D
SI: snubber diode equivalent circuit, D2: high speed diode, D1 = 9-purpose diode, C3: snubber capacitor, R8: snubber resistor, C1: capacitor, R1: resistor. Method 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1) A snubber circuit for absorbing overvoltage applied to a switching semiconductor device, the snubber circuit comprising: at least a capacitor; and a snubber circuit based on the current flowing through the switching semiconductor device when the device is turned off. a first diode that guides the energy of a stray inductance in series with the semiconductor device to the capacitor, a snubber circuit comprising a parallel circuit for the first diode, and a parallel circuit that includes at least the first diode and the first diode. 1. A snubber circuit for a switching semiconductor device, comprising a second diode having the same polarity and a shorter forward recovery time than the first diode.