JPS6258875A - Driving circuit for switching transistor - Google Patents

Abstract

PURPOSE:To actuate a switching transistor at a small loss and at a high speed by utilizing the corrector current as the base current of an NPN transistor flowing only during the carrier storage time when a switching transistor is turned off. CONSTITUTION:When the output of an oscillation circuit 21 becomes low, an NPN transistor 22 turns off and no base current is supplied to a switching transistor 29 while the corrector current keeps flowing only during the carrier storage time of the switching transistor 29. During this time the current induced to a current transformer 30 is charged into a condenser 25 through a diode 27. By this charged current the voltage is produced at the both ends of a resistance 26 and the base of an NPN transistor 23 is made a positive bias turning it ON. Thus with such a simplified constitution, the switching transistor can be turned off efficiently and at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a driving circuit for switching transistors.

BACKGROUND ART As a conventional technique, for example, as shown in the circuit diagram of FIG. 2, an NPN transistor 2 and a PNP transistor 3 are alternately turned on and off by an output signal from an oscillation circuit 1.
When NPN transistor 2 is on, current transformer 1
o supplies a base current proportional to the collector current to turn on the switching transistor 9, and when the PNP transistor 3 is on, the switching transistor 9
A method of pulling the pace to a negative potential is used.

The operation of the circuit shown in FIG. 2 will be explained below. The oscillation circuit 1 is a rectangular wave oscillation circuit. When the output of the oscillation circuit 1 becomes high, the NPN transistor 2 is turned on and current flows through the resistor 4 to the switching transistor 9. Then, the switching transistor 9 operates, and a current proportional to its collector current is obtained from the current transformer 1o, flows through the diode 7 and the NPN transistor 2 to the pace of the switching transistor 9, and generates the current necessary for the operation of the switching transistor 9. This provides a pace current. Next, when the output of the oscillation circuit 1 becomes low, the NPN transistor 2 is turned off, and the PNP transistor 3 whose base is driven to a negative potential via the resistor 16 is turned on, and the carrier accumulation time until all switching transistors are turned off is Collector current continues to flow. Therefore, a current proportional to this is induced in the current transformer 10. This current is charged to the capacitor 6 via the diode 7, and then discharged as the switching transistor 90 pace current when the output of the oscillation circuit 1 becomes high and the NPN transistor 2 is turned on.

Note that resistor 8 is a discharge resistance for the secondary side flyback voltage of current transformer 1o, 6 is a resistor, 11 is a load, 12 is an input terminal for power supply to the load, 13 is a bias power supply terminal including an oscillation circuit, and 14 is a ground. Terminal 15 is a reverse bias terminal.

Problems to be Solved by the Invention In the conventional circuit as described above, in order to turn off the switching transistor 9 more quickly, the PNP transistor 3 is
needs to be turned on quickly, and for this purpose a negative potential 16 is required, while the value of the resistor 17 must be made small, resulting in a large number of parts and a large loss in the drive circuit.

The present invention has been made in view of the above, and an object of the present invention is to provide a low-loss, high-speed switching transistor drive circuit with a simple circuit configuration and without using a negative potential.

Means for solving the problem of intermittent cough In order to solve the above-mentioned problem, the present invention solves the above-mentioned problem by
Instead of the NP transistor, connect the collector terminal of a second NPN transistor to the base terminal of the switching transistor, connect the emitter terminal of the second NPN transistor to the emitter terminal of the switching transistor, and connect the midpoint between the capacitor and the resistor. It is connected to the base terminal of the second NPN transistor to form a circuit that eliminates negative potential.

According to the circuit configuration of the present invention, when the switching transistor is turned off, a current proportional to the collector current flowing for the carrier accumulation time is obtained from the current transformer, and this current is used as the base current of the second NPN transistor. can be used. That is, the resistance and negative potential in the conventional circuit can be omitted, and a circuit configuration using a second NPN transistor instead of the PNP transistor can realize a low-loss, high-speed switching transistor drive circuit.

Embodiment FIG. 1 shows an embodiment of the circuit of the present invention. In FIG. 1, 21 is a square wave oscillation circuit, 22 and 23 are NPN transistors, 24 is a resistor, 25 is a capacitor, 2e is a resistor,
2γ is a diode, 28 is a resistor, 29 is a switching transistor, 30 is a current transformer, 31 is a load, 3
2 is an input terminal for power supply to the load 31, and 33 is an oscillation circuit 2.
Bias power supply terminals of this drive circuit including 1 and 34 are ground terminals.

The operation will be explained below. switching transistor 2
9 is on, that is, when the output of the oscillation circuit 21 is high, the operation is the same as that of the conventional circuit example described above. When the output of the oscillation circuit 21 becomes low, the NPN transistor 22 is turned off, the base current is no longer supplied to the switching transistor 29, and the switching transistor 2
The collector current continues to flow for the carrier accumulation time of 9.

During this time, the current induced in the current transformer 3o charges the capacitor 26 via the diode 27. This charging current generates a voltage across the resistor 26, and N
The base of the PN transistor 23 is positively biased, and the NPN
Transistor 23 turns on. That is, during the carrier accumulation time until the switching transistor 29 is completely turned off, the NPN transistor 23 continues to be on and draws a reverse base current from the switching transistor 29.
The switching transistor 29 is quickly turned off.

Effects of the Invention As described above, according to the present invention, a switching transistor can be turned off efficiently and at high speed with a simple circuit configuration, which is extremely useful.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of a switching transistor drive circuit according to an embodiment of the present invention, and FIG. 2 is an electrical circuit diagram showing an example of a conventional circuit. 21...Oscillation circuit, 22...NPN
Transistor, 23...Transistor, 24.
...Resistor, 25...Capacitor, 26.
Old...Resistance, 27...Diode, 28...
...Resistor, 29...Switching transistor, 3o...Current transformer, 31 Old...
Load, 32... Power supply terminal, 33 Old... Bias terminal, 34... Earth terminal.

Claims (1)

[Claims] In a drive circuit that uses a current transformer to detect a collector current of a switching transistor, extracts a current proportional to the collector current, and drives the switching transistor in synchronization with an output signal of an oscillation circuit, the output of the oscillation circuit is a terminal connected to a base terminal of a first NPN transistor, an emitter terminal of the first NPN transistor connected to a base terminal of the switching transistor, and a collector terminal of a second NPN transistor; The emitter terminal of the transistor is connected to the emitter terminal of the switching transistor, the series circuit of a capacitor and a resistor is connected to the collector terminal of the first NPN transistor, and the second NPN transistor is connected to the middle point of the connection between the capacitor and the resistor. The base terminal of the transistor is connected, and the other end of the resistor is connected to a second N
1 of the current transformer is connected to the emitter of the PN transistor, and the collector terminal of the switching transistor is connected to the emitter of the PN transistor.
The end point of the next winding is connected, the start point of the primary winding of the current transformer is connected to the load, and the start point of the secondary winding of the current transformer is connected to the collector terminal of the first NPN transistor. and a switching transistor drive circuit, wherein a winding end point of a secondary winding of the current transformer is connected to an emitter terminal of the switching transistor.