JPH05145387A - Base drive circuit - Google Patents

Abstract

PURPOSE:To drive a high hFE power transistor(TR) with a very high output even when the maximum output current of a base drive IC is not sufficient. CONSTITUTION:This circuit is provided with a bypass TR 26 to bypass n part of the reverse base current 43 of a high hFE power TR 22. The emitter is connected to the base of the high hFE power TR 22 via a base current limit resistor 24, the base is connected to a base drive IC2 and the collector is connected to the negative pole 13 of a reverse bias power supply 25 respectively. Moreover, a bias resistor 27 is connected between the emitter and the collector of the TR 26 to supply a base current 45 to the TR 26 when an output current 44 flows to the TR 32 of the base drive IC 21. The base current 45 is amplified by the TR 26 to generate a reverse base current 43 resulting from adding the amplified current 46 to an output current 44.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base drive circuit applied to drive a high hFE power transistor.

[0002]

2. Description of the Related Art Conventionally, this type of base drive circuit has been constructed as shown in FIG. In FIG. 2, reference numeral 21 is a base drive IC incorporating a pair of transistors 31 and 32, and 22 is a high hFE power transistor driven by the base drive IC 21. Transistor 3
The emitter (E) of 1 and the collector (C) of the transistor 32 are commonly connected.

The base drive IC 21 has input terminals 1 and 2 to which an input signal 41 for determining the operating state of the IC 21 is input, a terminal 3 connected to the collector (C) of the transistor 31, and a transistor 31. A terminal 4 connected to the common connection point of the emitter (E) and the collector (C) of the transistor 32, a terminal 5 connected to the emitter (E) of the transistor 32, and a terminal 6 connected to the positive electrode 8 of the power supply. , And a terminal 7 connected to the negative electrode 9 of the power supply.

A base current limiting resistor 23 for limiting the forward base current is connected between the terminal 3 of the base drive IC 21 and the power supply positive electrode 8, and the terminal 4 of the IC 21 is connected.
A base current limiting resistor 24 is connected between the base and the base (B) 10 of the high hFE power transistor 22. The negative electrode 13 of the reverse bias power supply 25 is connected to the terminal 5 and the power supply negative electrode 9 of the base drive IC 21, and the positive electrode 14 of the reverse bias power supply 25 is connected to the emitter (E) 11 of the high hFE power transistor 22. There is.

Now, in the conventional base drive circuit shown in FIG. 2, when the input signal 41 input to the input terminals 1 and 2 of the base drive IC 21 is turned on, the pair of transistors in the base drive IC 21 are turned on. 31, 3
The transistor 31 of 2 turns on, and the base current limiting resistor 23 in the forward direction from the power supply positive electrode 8 and the base drive IC
21 terminal 3, collector (C) to emitter (E) of transistor 31, terminal 4 of base drive IC 21, base current limiting resistor 24, high hFE power transistor 22.
A forward base current 42 flows in the power supply negative electrode 9 through the base (B) 10 through the emitter (E) 11 and the reverse bias power supply 25 in order.

On the contrary, the input signal 41 input to the input terminals 1 and 2 of the base drive IC 21 is turned off (OF
In the F) state, the transistor 32 is turned on,
From the positive electrode 14 of the reverse bias power supply 25 to the emitter (E) 11 of the high hFE power transistor 22 and the same transistor 2
2 through the base (B) 10, the base current limiting resistor 24, the terminal 4 of the base drive IC 21, the collector (C) to the emitter (E) of the transistor 32, and the terminal 5 of the base drive IC 21 in this order, and the reverse bias power supply. 25
The reverse base current 43 flows through the negative electrode 13 of the.

[0007]

In the conventional base drive circuit shown in FIG. 2 described above, the forward base current 4
2 and the maximum value of the reverse direction base current 43 are determined by the maximum output current of the base drive IC 21. However, with the maximum output current of the base drive IC 21 currently available, if an attempt is made to drive a high hFE power transistor of 50 A to 150 A class with the base drive IC 21,
The forward base current 42 has a sufficient current value and there is no problem, but the reverse base current 43 has a problem that the current value is insufficient and cannot be applied.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a base drive circuit capable of driving an extremely high output high hFE power transistor even if the maximum output current of the base drive IC is not sufficient. Especially.

[0009]

The present invention, as shown in FIG. 1, is a base drive IC for driving a high hFE power transistor 22 according to ON / OFF of an input signal 41.
21, a base current limiting resistor 24 having one end connected to the base 10 of the power transistor 22, and a reverse bias power supply 25 for reverse biasing between the base 10 and the emitter 11 of the power transistor 22. In addition, a bypass transistor 26 for bypassing a part of the reverse direction base current 43 flowing through the base current limiting resistor 24, and a bias resistor 27 connected between the emitter and the base of the bypass transistor 26 are newly provided. , The other end of the base current limiting resistor 24 is the emitter of the bypass transistor 26, the base drive IC 21 is the base, and the reverse bias power supply 25 is the collector.
The feature is that they are connected to each other.

[0010]

In the above configuration, in the mode in which the reverse direction base current 43 is taken out from the base 10 of the high hFE power transistor 22 to the base current limiting resistor 24 according to the state of the input signal 41, the output current 44 of the base drive IC 21
As a result, a potential difference is generated across the bias resistor 27, and the emitter and base of the bypass transistor 26 are biased. As a result, a part of the output current of the base drive IC 21 becomes part of the base current 45 of the bypass transistor 26.
As it flows from its emitter to its base. The base current 45 is amplified by the transistor 26. As a result, an amplified current 46 flows from the emitter of the transistor 26 to the collector, and a current obtained by superposing the current 46 and the output current 44 of the base drive IC 21 flows as a reverse base current 43 through the base current limiting resistor.

[0011]

1 is a diagram showing the configuration of a base drive circuit for a high hFE power transistor according to an embodiment of the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted.

In FIG. 1, 26 is the reverse base current 4
3 is a bypass transistor that bypasses a part of 3.
The transistor 26 is provided in order to generate a sufficiently large reverse base current 43 by amplifying the base current 45 which is a part of the current 44 flowing through the transistor 32 of the base drive IC 21.

Base (B) of bypass transistor 26
Is connected to the terminal 4 of the base drive IC 21, and the collector (C) is commonly connected to the terminal 5 of the base drive IC 21, the power supply negative electrode 9 and the negative electrode 13 of the reverse bias power supply 25. The emitter (E) of the transistor 26 is
One end is the base (B) 1 of the high hFE power transistor 22.
It is connected to the other end of the base current limiting resistor 24 connected to 0. Furthermore, the base (B) of the transistor 26
A bias resistor (bias resistor) 27 is connected between the emitter and the emitter (E).

Reference numeral 44 is a current (output current of the base drive IC 21) flowing through the transistor 32 (from the collector to the emitter) of the base drive IC 21 when the input signal 41 is on, and 45 is a base current of the bypass transistor 26. Reference numeral 46 indicates the bypass transistor 26 (from the emitter to the collector) when the input signal 41 is on.
It is a flowing current (a bypass current of the reverse direction base current 43).

Next, the operation of the configuration shown in FIG. 1 will be described. First, when the input signal 41 input to the input terminals 1 and 2 of the base drive IC 21 is turned on (ON),
A pair of transistors 31 in the base drive IC 21,
The transistor 31 out of 32 is turned on, and the base current limiting resistor 23 in the forward direction from the power supply positive electrode 8 and the base drive I
Terminal 3 of C21, collector (C) to emitter (E) of transistor 31, terminal 4 of base drive IC21,
Bias resistor 27 and base current limiting resistor 24, high hFE
A forward base current 42 flows in the power supply negative electrode 9 through the base (B) 10 of the power transistor 22, the emitter (E) 11, and the reverse bias power supply 25 in order. The operation when the input signal 41 is on is the same as in the conventional example of FIG.

Next, the operation when the input signal 41 input to the input terminals 1 and 2 of the base drive IC 21 is turned off will be described. When the input signal 41 is off, the transistor 32 of the pair of transistors 31 and 32 in the base drive IC 21 is turned on. Then, from the positive electrode 14 of the reverse bias power supply 25, through the emitter (E) 11 of the high hFE power transistor 22, to the base (B) 10 of the transistor 22, the base current limiting resistor 24, the bias resistor 27, the base drive IC 21.
A current (output current of the base drive IC 21) 44 flows to the negative electrode 13 of the reverse bias power supply 25 through the terminal 4, the collector (C) of the transistor 32, the emitter (E), and the terminal 5 of the base drive IC 21.

When the input signal 41 is turned off and the output current 44 of the base drive IC 21 flows as described above, a potential difference (having a positive potential at the connection point with the emitter of the transistor 26) is applied across the resistor 27. Occurs. As a result, the emitter (E) and the base (B) of the bypass transistor 26 are biased, and the base current 45 flows from the emitter (E) of the transistor 26 to the base (B). The base current 45 is amplified by the transistor 26, and the amplified current 46 flows from the emitter (E) of the transistor 26 through the collector (C) to the negative electrode 13 of the reverse bias power supply 25.

As a result, the base current limiting resistor 24 has
Output current of the base drive IC 21 (transistor 32
Current flowing through the transistor 26) 4
The reverse base current 43 with 6 superposed flows.

As described above, according to this embodiment, the input signal 4
When 1 is off, the output current 44 of the base drive IC 21 is a current 4 obtained by amplifying the base current 45 forming a part of the current 44 by the transistor 26.
A sufficiently large reverse base current 43 to which 6 is added passes from the positive electrode 14 of the reverse bias power supply 25 through the emitter (E) 11 of the high hFE power transistor 22 and further to the base (B) 10 and base current of the transistor 22. Limiting resistor 2
4 to the negative electrode 13 of the reverse bias power supply 25.

[0020]

As described in detail above, according to the present invention, a bypass transistor for bypassing a part of the reverse base current of the high hFE power transistor driven by the base drive IC is provided, and the base drive I
Since a part of the output current of C is amplified as the base current of the bypass transistor, the current obtained by adding the amplified current to the output current of the base drive IC can be used as the reverse base current of the high hFE power transistor. it can.

Therefore, even if the maximum output current of the base drive IC is not sufficient, it is possible to drive an extremely high output high hFE power transistor of 50 A to 150 A class, which has been difficult to apply conventionally.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a base drive circuit of a high hFE power transistor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional base drive circuit.

[Explanation of symbols]

21 ... Base drive IC, 22 ... High hFE power transistor, 23 ... Forward base current limiting resistor, 24 ... Base current limiting resistor, 25 ... Reverse bias power supply, 26 ... Bypass transistor, 27 ... Bias resistor, 42 ... Forward base current, 43 ... Reverse base current, 44 ... Current (output current of base drive IC 21), 45 ... Base current, 46 ... Current (current flowing through transistor 26, bypass base current 43 bypass current).

Claims (1)

[Claims] 1. A base drive IC for driving a high hFE power transistor according to on / off of an input signal.
A base current limiting resistor whose one end is connected to the base of the power transistor, and a reverse bias power supply for reverse biasing between the base and emitter of the power transistor, depending on whether the input signal is turned on or off. A base drive circuit for supplying a forward base current to the base of the power transistor or for extracting a reverse base current from the base of the power transistor, an emitter connected to the other end of the base current limiting resistor,
A bypass transistor having a base connected to the base drive IC and a collector connected to the reverse bias power supply, for bypassing a part of a reverse direction base current flowing through the base current limiting resistor; And a bias resistor connected between the emitter and the base of, and amplifying a part of the output current of the base drive IC as the base current of the bypass transistor,
A base drive circuit, wherein the amplified current is made a part of the reverse base current.