JPS6013329B2 - High power switching transistor drive device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving device for a high-power switching transistor, and in particular, in a DC-DC converter or the like, a current exceeding the maximum current or a set current may flow through the collector of the high-power switching transistor depending on the load condition. The present invention relates to a driving device for a high-power switching transistor that promptly turns off and protects the transistor when the transistor is in use.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit connection diagram showing an embodiment of the present invention.
indicates a high power switching transistor.

The collector of this transistor TR is the output transformer T,
is connected to a power source E through a primary winding F, and its emitter is grounded through a resistor R2. Further, the base is connected to one end of the secondary winding S2 of the drive transformer T2 via a parallel circuit of a resistor R3 and a capacitor C, and the other end of this secondary winding S2 is grounded. A series circuit of a resistor R7 and a capacitor C2 is connected to the primary winding F of the output transformer T, and the secondary winding S is connected to the load L. One end of the primary winding F2 of the drive transformer T2 is connected to one end of the power supply E2 via a resistor R, and the other end of the primary winding F2 is connected to the high power switching transformer TR.
, the collector of the base drive transistor TR2,
The anode of the SCR, the Zener diode, the varistor, etc. are each connected to an element A whose resistance value against voltage rapidly decreases. Base drive transistor T
The base of R2 is connected to one end of the drive source PR via a resistor R4, and is connected to the drive source DR via a resistor R5.
connected to the other end. The other end of power supply E2 and drive source DR
The other end is connected in common, and the emitter of the transistor TR2 and the cathode of the SCR are also connected to the other end of the drive source DR, and the element A is further connected to the other end of the drive source DR via a resistor R6. . A series circuit of a resistor R8 and a capacitor C3 is connected to the primary winding F2 of the drive transformer T2. As shown in the figure, the connection polarity of the drive transformer L is an on-off type (when the primary side transistor TR2 is on, the secondary output is off). Next, the operation will be explained.

First, the operation when the emitter resistance R2 of the high-power switching transistor TR is O, that is, the emitter of the transistor TR is directly grounded will be described.

When the drive output shown in FIG. 2A is generated from the drive source DR of the transistor TR2, the collector voltage waveform of the transistor TR2 (waveform at point a in FIG. 1) becomes as shown in FIG. 2B. Now, assuming that the transistor TR2 is on at Cape Tokiya and off at time t2, the primary current i of the drive transformer T2 becomes as shown in Figure 2C at time t, ~. At time t2, the transistor TR2 turns off, so the primary current i, of the transformer T2 also turns off, and therefore, due to the magnetic flux stored in the transformer T2, N.j,2
At time t2, current t22 flows through the secondary side of transformer T2 so as to satisfy =N2·j22. The secondary current i2 of the transformer T2 is as shown in FIG. 2D. Note that N and N2 are the primary winding and secondary winding F2 of the transformer T2.
and the number of turns of S2. Thus, at a certain time, the transformer T2 becomes a constant current source, and as a result, the transistor T2 becomes a constant current source.
The voltage at the collector of R2 (voltage at point a) is expressed by the following equation. VaiE2 10 mothers (〉Spot・10V・〉 ......'1
) Here, E2 is the drive power supply voltage, and (V8E, 10V
, ) is the potential drop on the secondary side due to the flow of i2.

Next, when an emitter resistor R2 is inserted into the high power switching transistor TR as shown in the figure, a current equal to the sum of the collector current IC of the transistor TR and the base drive current i2 flows through the resistor R2.

However, in this case as well, since the primary side current j, reaches 1.2 at time t2, N.・i,
The current i22 that satisfies 2=N2・i22 is the transformer T2.
flows to the secondary side of As a result, the m formula becomes as follows. V
a′=E20 mother {V. 10VBE1R2kui20iC)}
‐‐‐‐‐・‐・‐'2}Now, i
Ignoring VB8 due to the variation of c, va' = {E2 ten mother (v, ten v BE + R2 i2)} Juo book・iC=K・ten K2・iC ……I3'K here,;E2 ten mother W.
10VBE+R2-i2)K2=Nze.

That is, by inserting the emitter resistor R2, the voltage at point a (collector voltage of transistor TR2) becomes a linear function of IC. This relationship is shown in FIG. 3. This means that the collector current ic of the transistor TR appears as a voltage on the primary side of the drive transformer T2. The present invention focuses on this point, and in the embodiment shown in FIG. 1, a resistor R6 is connected in series between the collector of the drive transistor TR2 and the emitter to provide a voltage resistance of a Zener diode, a varistor, etc. An element A that rapidly decreases at a point is inserted, and this element A detects that the collector current IC of the switching transistor TR has flowed beyond a preset value, and equivalently turns on the drive transistor TR2. As a result, the switching transistor TR is turned off to protect the switching transistor TR.

In the embodiment of FIG. 1, the high power switching transistor T
When the collector current IC of R, exceeds a predetermined setting value, the element A suddenly decreases its resistance value at the collector voltage Va' of the drive transistor TR2, that is, becomes conductive. Since it has been selected,
Due to the conduction of element A, a voltage is generated across the resistor R6,
This voltage turns on the SCR.

Turning on the SCR means that the drive transistor TR2
This is equivalent to turning on the drive transformer T2.
The polarity of the secondary output voltage of is reversed, and the high power switching transistor TR is turned off. The switching transistor TR is thus protected. Drive transistor TR with the next drive pulse from drive source DR
When 2 is turned on, the SCR is turned off and automatically returns to its original state. Note that the resistance R, is the transformer primary current i,
is the current limiting resistor. FIG. 4 shows an example in which the present invention is applied to a switching regulator, and a portion B surrounded by a dotted line in the figure is an error intensifier and a pulse width conversion circuit.

Since the operation of this circuit portion B is well known, its explanation will be omitted. In this embodiment, when the collector current IC of the switching transistor (not shown) flows beyond a set value,
Since element A is conductive, transistor TR5 is turned on. Since the capacitor C is short-circuited when the transistor TRs is turned on, the transistor TR3 is turned off and the drive transistor TR2 is turned on. As a result, as described above, the polarity of the secondary output voltage of the drive transformer T2 is reversed, and the switching transistor is turned off and protected. As described above, according to the present invention, by focusing on the fact that a change in the collector current of a high-power switching transistor appears as a change in the collector voltage of a drive transistor, a Zener diode whose resistance value with respect to voltage rapidly decreases is developed. , this voltage change is detected by a device such as a varistor,
Since it equivalently turns on the drive transistor and turns off the high power switching transistor,
It is possible to reliably protect large-scale switching transistors.

In addition, since it simply uses an element whose resistance value changes rapidly with respect to voltage, there are many notable advantages such as no manufacturing problems, low cost, and ease of application to off-the-shelf devices. There is.

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing an embodiment of a driving device for a high-power switching transistor according to the present invention. FIG. 2 is a various waveform diagram for explaining the operation of the circuit shown in FIG. 1, and FIG. 3 is a diagram similar to that shown in FIG. FIG. 4 is a characteristic diagram showing the relationship between the collector current of the high-power switching transistor and the collector voltage of the drive transistor in FIG. 4, and FIG. 4 is a circuit connection diagram showing another embodiment of the present invention. TR in the figure is a high power switching transistor, TR
2 is a drive transistor, T is an output transformer, L
is a drive transformer, L is a load, A is an element whose resistance value drops rapidly with respect to voltage, DR is a drive source, and R2 is an emitter resistance of a high power switching transistor. Figure 1 Figure 3 Figure 2 Figure 4

Claims (1)

[Claims] 1 A drive transistor, a high power switching transistor that operates on or off according to a signal input to its base, and a high power switching transistor in which the drive transistor is connected to the primary side and the high power switching transistor is connected to the secondary side voltage. and a drive transformer whose polarity is selected so that the high power switching transistor is turned off when the drive transistor is on, and a collector voltage of the drive transistor is 1. A driving device for a high-power switching transistor, comprising an element circuit that suddenly turns on and lowers the collector voltage when a voltage corresponding to a collector current value exceeding a predetermined set value is reached.