JPH01218123A - Driving circuit for semiconductor switch - Google Patents

Abstract

PURPOSE:To reduce the voltage capacity of a current transformer by inserting a feedback circuit use semiconductor switch subject to on/off control in response to the operation of the semiconductor switch of a main circuit depending on a voltage across a resistor connected with a control power supply for charging the capacitor to a feedback circuit supplying a base current to a transistor(TR) of the semiconductor switch. CONSTITUTION:The secondary winding 3b of the current transformer 3 is connected between the base and emitter E of the TR 1 of the semiconductor switch to supply a base current to the TR 1 by a feedback circuit, to which the feedback circuit use semiconductor switch 11 operated with the voltage across the resistor 12 connected with the control power supply 16 for charging the capacitor 4 as the control voltage is inserted newly. Then the feedback circuit use semiconductor switch 11 is turned on when the semiconductor switch 2 of the main circuit is turned on, the capacitor 4 is discharged, the voltage is dropped and the voltage across the resistor is increased conversely and when the semiconductor switch 2 of the main circuit is turned off, the switch 11 is turned off. Thus, the drive circuit for the semiconductor switch to reduce the capacity of the feedback current transformer is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor switch formed by connecting a bipolar transistor and a MOSFET in series, and particularly to a drive circuit for a current transformer feedback system.

[Prior art] FIG. 4 shows, for example, an INTERNATIONAL RECT
This is a basic circuit diagram of this type of semiconductor switch shown in Page (published in 1982).

In the figure, a bipolar transistor (hereinafter simply referred to as a transistor) (1) and a MOSFET+21 constitute a semiconductor switch by connecting the emitter E of the transistor (1) and the drain D of the MOSFET (2).

(3) is a current transformer whose primary winding (3a) is connected between the collector of the transistor (1) and the terminal P.
One end of the next winding (3b) is connected to the source S of the MOSFET (2), and the other end is connected to the base B of the transistor (1) via the diode (6). The source S of 2) is connected to the terminal N. (4) and (5) are transistors (
1) A capacitor and a Zener diode connected between the base B and the terminal N, +71 +81 a diode and a resistor respectively connected between the collector C and the base B of the transistor (1), +9111 the terminal PN A DC power supply and a load are respectively connected between them.

Next, the operation will be explained with reference to FIG. First, before time t1, the gate voltage Vos of MOSFET (21) is zero, the transistor (1) and MOSFET (21 are in the off state, and the current transformer (3)
primary winding (3a), diode (7) and resistor (8
), and the voltage Vc across it is clamped to about 15V by the Zener diode (5). Next, at time t1, M OS F
When the gate voltage Vos of E T +21 is raised from zero to a certain positive value and the MOSFET (21 is turned on,
Capacitor (4) to transistor (1) and M O
Since the discharge current, that is, the base current In flows through S F E T +21, the transistor (1) is also turned on immediately. As a result, the collector current Ic of the transistor (1) begins to flow from the DC power supply (9) through the load QG. At this time, if the turns ratio of the current transformer (3) is n, a current of IcTz = Ic /n flows through its secondary winding (3b), and this current flows through the diode (61,) transistor (
1) and MOSFET+21. Therefore, the base current In is supplied to the transistor (1) by the positive feedback action of the current transformer (3), and the transistor (1)
remains on.

Next, at time t2, the gate voltage V of MOSFET f21
When G8 is returned from positive to zero, M OS F E T 121
turns off immediately. As a result, the transistor (1
) is substantially open, so the collector current Ic passes from the collector C to the base B and flows into the capacitor (4) and Zener diode (5).

At this time, the - capacitor (4) acts as a means for suppressing the switching surge voltage between the drain D and source S of MOSFET+21. Then, at time t3 when the blocking ability between the collector C and the base 8 of the transistor (1) is restored, the collector current Ic is cut off, and the transistor (1)
M OS F E T (21b Yohi current transformer f31
(D The voltage Vpy across the series body rises to the level of the DC power supply voltage ME and returns off.

[Problem to be solved by the invention]

In the conventional semiconductor switch drive circuit, as described above, both ends of the secondary winding (3b) of the current transformer (3) are connected to the transistor (1).
) base B, l! : Since it is connected between the source s of MO8FET (2), the iron core used for the current transformer (3) is the base B and emitter 8 of the transistor (1).
It is necessary to make the voltage-time integral value not saturated by adding the voltage drop between the drain D and the source S of MOSFET+21 to the voltage drop between them.

By the way, the MOSFET (drain D and source S of 21)
Since the load current itself flows between them, the voltage drop that occurs in this part reaches a considerable value, and the current transformer (3) needs to be correspondingly large, which is disadvantageous in terms of economy and efficiency. there were.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a drive circuit for a semiconductor switch that can reduce the capacity of a current transformer for feedback.

[Means and effects for solving the problems] A semiconductor switch drive circuit according to the present invention.

A feedback circuit connects the secondary winding of the current transformer between the base and emitter of the transistor of the semiconductor switch to supply base current to the transistor, and a resistor connected between the control power supply and the control power supply for charging the capacitor. A semiconductor switch for the feedback circuit that operates using the voltage as the control voltage is newly inserted. - When the semiconductor switch in the main circuit is turned on, the semiconductor switch for the feedback circuit is turned on because the capacitor discharges and its voltage drops, and conversely the voltage applied to the resistor increases, and the semiconductor switch in the main circuit turns off. Then, the capacitor is charged and its voltage increases, and the voltage applied to the resistor decreases, turning it off.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In Figure 1, (1) to 6) and (91(1)
Since 0 is the same as the conventional one, the explanation will be omitted. However, the lower end of the secondary winding (3b) of the current transformer (3) is connected to the transistor (1
) is connected to the emitter E of The circle is MO for the feedback circuit
5FET, its drain is connected to the cathode of the diode (6), and its source is connected to the base of the transistor (1). fLl 13 is M OS F E T
A resistor and a diode are connected in parallel between the gate and source of +Ill, respectively (141 is a MOSFE
The capacitor connected between the gate of T (Ill and the source of MOSFET (21) is connected in parallel with the control power supply (161) and the capacitor (1), and its signal output is the drive signal generation circuit. FET (2
It is input to gate G of 1.

Next, the operation will be explained with reference to FIG.

When the transistor (1) and MOSFET (21) are off, the capacitor (4) is charged by the control power supply 0e or the capacitor (14) via the resistor 0X5, and the voltage Vc across it is approximately 1
It is clamped to about 5V. Next, at time t1, the MOS
When the gate voltage vGS of the FET (2) is raised from zero to a certain positive value and the MOSFET +2+ is turned on, a discharge current from the capacitor (4) to the transistor (1) and the MOSFET [21, that is, the base current IB
flows, so the transistor turns on immediately. Capacitor (4) is discharged and MOSFET
(t) The source potential of J is the voltage between base B and emitter E of transistor (1) and M OS F E T +21
The sum of the voltages between the drain D and the source 28 drops to a value of about several volts. As a result, if the voltage of the control power supply α0 is 15V, the gate of MO5FETIII has a voltage of more than 10 V.
Since a positive voltage has been applied to the device, it immediately turns on. At the same time, the collector current Ic of the transistor (1) starts flowing from the DC power supply (9) through the load 0α.

If the turns ratio of the current transformer (3) is n, its secondary winding (3b) is ICT! A current of = Ic /n flows through the diode (6) and the MOS FET (
111O, J: Freewheeling the human 57 transistor (1) and supplying the base current IB to the transistor (1) by positive feedback action to maintain the on state of the transistor (1). Particularly in this case, a large load current (collector current Ic) flows through the secondary winding (3b) of the current transformer (3).
The voltage drop at E T +21 is not added, and the newly added voltage drop at MO8FET αD is small because its current 1cTt is 1/n times the load current Ic.
As a result, the voltage rating of the secondary winding (3b) of the current transformer (3) can be significantly reduced compared to the conventional one.

Next, at time t2, MOSFET (2)
When the gate voltage Vas of MO3F E is returned from positive to zero, MO3F E
T+21 turns off immediately. As a result, the circuit of the emitter E of the transistor (1) becomes substantially open, and the collector current Ic flows from the collector C to the base B, passing through the capacitor (4) and the Zener diode (5).
). This is the same as the conventional case, but MOSFET
For ET (Ill), the voltage of the Zener diode (5) is clamped to 15V, which is equivalent to the voltage of 15V of the control power supply (161), so the voltage between the gate and source of the resistor (12) is approximately becomes zero, MOSFETd
ll is turned off, and the secondary circuit, ie, the feedback circuit, of the current transformer (3) becomes open. The subsequent operation is the same as the conventional one, and will therefore be omitted.

In addition, FIG. 3 shows the MOS FET in FIG. 1.
(11) is replaced by a transistor αη, and the same operation and effect as in FIG. 1 is achieved.

〔Effect of the invention〕

As described above, according to the present invention, the voltage applied to the resistor connected between the feedback circuit that supplies the base current to the transistor of the semiconductor switch and the control power supply for charging the capacitor causes the semiconductor switch of the main circuit to be activated. By inserting a semiconductor switch for the feedback circuit that is controlled on and off according to the operation, the MOSFET in the main circuit through which a large load current flows
This has the effect that the voltage drop in the current transformer is not applied to the secondary winding of the current transformer, and the voltage capacity of the current transformer can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a semiconductor switch driving circuit according to an embodiment of the present invention. FIG. 2 is a time chart explaining the operation of the circuit of FIG. 1. FIG. FIG. 4 is a circuit diagram showing a drive circuit for a semiconductor switch, FIG. 4 is a circuit diagram showing a conventional semiconductor drive circuit, and FIG. 5 is a time chart illustrating the operation of the circuit shown in FIG. 4. In the figure, (1) is a transistor, (2) is a MOSF
E.T. (a) (3a) and (3b) are a current transformer, its primary winding and its secondary winding, respectively, (4) is a capacitor, (
6) is a diode, (2) is a feedback MO5FET, (L
3 is a resistor, and αQ is a control power source. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Masu Oiwa, Patent Attorney 1 diagram for female! , transistor δ tie wire Jb
Henkabo L Iwama02nKatsusen4, )/Den V Fig. 2 11 τ2τ374 Fig. 3 ρ

Claims (1)

[Claims] A semiconductor switch configured by connecting a transistor and a MOSFET in series by connecting their emitters and drains to the main current path, and a primary winding connected in series with the semiconductor switch. A current transformer in which one end of a secondary winding is connected to the base of the transistor via a diode, and the other end of the secondary winding is connected to the emitter of the transistor, forming a feedback circuit that supplies base current to the transistor. , the base of the transistor and the MO
In a semiconductor switch drive circuit comprising a capacitor connected between the source of the SFET and a control power supply connected to the capacitor via a resistor, the voltage applied to the resistor is inserted into the feedback circuit as a control voltage, When the semiconductor switch is turned on, the voltage applied to the resistor increases due to the discharge of the capacitor, and the semiconductor switch turns on.
A drive circuit for a semiconductor switch, comprising a feedback circuit semiconductor switch that turns off due to a voltage drop across the resistor based on charging of the capacitor when the semiconductor switch is turned off.