JPH01122368A - Driving circuit for switching transistor - Google Patents

Abstract

PURPOSE:To improve the efficiency of a power source by applying a reset signal having the same pulse width as that of a pulse width modulation signal for exciting a pulse transformer to the transformer in synchronization with the fall of the modulation signal. CONSTITUTION:A driving circuit for a switching transistor(Tr) has first-second sawtooth wave oscillators 1-2, first second comparators 3-4, first-second pulse transformer exciting Trs 5-6, a pulse transformer 7, a Tr driving power source 8, a synchronizing signal generator 9, and a switching Tr 10. The Tr 5 outputs a reset pulse signal for turning OFF the Tr 10 to the transformer 7, and the Tr 6 outputs an exciting pulse signal to turn ON the Tr 10. An output voltage control signal (a) becomes a signal (c) pulse-width-modulated through the comparator 3, and the transformer 7 is reset by the reset signal having the same pulse width as that of the signal (c).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a switching transistor drive circuit,
In particular, the present invention is suitable for switching transistor drive circuits suitable for use in power supply circuits such as switching power supplies.

[Prior Art] Conventionally, when it is necessary to isolate a power supply control circuit and a switching transistor in a power supply circuit, etc., a switching transistor drive circuit using a pulse transformer has been used.

FIG. 3 is a block diagram of a conventional switching transistor drive circuit, and FIG. 4 is a timing chart showing signals of various parts in the switching transistor drive circuit of FIG.

In FIG. 3, 11 is a sawtooth wave oscillator, 12 is a comparator, 13 is a pulse transformer excitation (excitation) transistor, 14 is a pulse transformer reset diode, 15 is a pulse transformer that isolates the power supply control circuit and the main circuit, 16 is a switching transistor, and 17 is a power supply for driving the switching transistor.

In the above configuration, the sawtooth oscillator 11 and the comparator 12
performs pulse width modulation according to the output voltage control voltage,
The temporary side winding of the pulse transformer 15 is excited by the pulse width modulation signal. On the other hand, a pulse transformer reset diode 14 connected to the reset winding of the pulse transformer 15 applies a reset. Then, the switching transistor 16 is driven by the voltage appearing on the secondary side of the pulse transformer 15 in this manner.

The conventional switching transistor drive circuit drives the switching transistor as described above.

[Problems to be solved] The conventional switching transistor drive circuit described above is
Since the energy stored in the pulse transformer was reset by the pulse transformer reset diode, if the pulse width of the signal transmitted through the pulse transformer is narrow, the fall time of the voltage appearing on the secondary side of the pulse transformer is slow, resulting in a negative voltage. Since the voltage is not drawn sufficiently to the side, there is a problem that the turn-off time of the switching transistor becomes longer and the power supply efficiency deteriorates.

The present invention has been made in view of the above-mentioned problems, and is a switching transistor that shortens the turn-off time of a switching transistor and does not cause deterioration in power supply efficiency even when the pulse width of a signal transmitted through a pulse transformer is narrow. The purpose is to provide drive circuits.

[Means for Solving Problems] In order to achieve the above object, a switching transistor drive circuit of the present invention performs pulse width modulation according to a pulse transformer and a control input, outputs an excitation pulse signal to the pulse transformer, and , and pulse width modulation means for outputting a reset pulse signal immediately after the excitation pulse signal falls.

[Example] Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a block diagram of a switching transistor drive circuit according to an embodiment of the present invention.

In the figure, 1. 2 are first and second sawtooth wave oscillators, 3 and 4 are first and second comparators, 5.6 are first and second pulse transformer excitation transistors, and 7
8 is a pulse transformer, 8 is a power supply for driving a switching transistor, 9 is a synchronizing signal generation circuit, and 10 is a switching transistor in the switching power supply.

Here, the first pulse transformer excitation transistor 5 outputs a reset pulse signal to the pulse transformer 7 to turn off the switching transistor 10, and the second pulse transformer excitation transistor 6 outputs a reset pulse signal to the pulse transformer 7 to turn off the switching transistor 10. An excitation pulse signal is output to the pulse transformer 7 to turn on the switching transistor 10.

In the above configuration, the output voltage control signal (control input) a is compared with the sawtooth wave generated by the first sawtooth wave oscillator 1 in the first comparator 3, and the output voltage control signal a is pulse width modulated. A signal C is generated.

Further, the synchronization signal generation circuit 9 generates a synchronization signal d synchronized with the rise of the signal C, and sends it to the second sawtooth wave oscillator 2. Then, the second sawtooth wave oscillator 2 generates a sawtooth wave e, which has the same waveform (frequency, amplitude) as the sawtooth wave generated by the first sawtooth wave oscillator 1 and is synchronized with the synchronization signal d. Sends to comparator 4. Roughly speaking, the second comparator 4 compares the sawtooth wave e and the output voltage control signal a, and generates a signal f that is pulse width modulated with respect to the output voltage control signal a.

Note that the ``synchronization signal f'' output in this way has almost the same waveform (frequency, pulse width) as the signal C, and
The phase is delayed with respect to signal C by (period of signal C - pulse width of signal C).

The signals C and f drive the first and second pulse transformer excitation transistors 5.6, respectively.

As a result, the pulse transformer 7 receives the voltage amplitude signal g of the switching transistor driving power supply 8 by switching the -time winding.
The switching transistor 10 is driven by the signal i excited by h and appearing on the secondary side.

Next, the second (!I) is a timing chart showing signals of various parts in the switching transistor drive circuit of FIG.

Here, the frequency of the sawtooth wave e is sufficiently large relative to the rate at which the output voltage control signal a changes. Therefore, it can be assumed that a signal C having a pulse width d0 equal to the pulse width d of the signal f is generated from the first comparator 3 in synchronization with the fall of the output signal f of the second comparator 4. can.

Therefore, immediately after the pulse transformer 7 is excited with the pulse width of the signal f by the pulse of the signal f, it is reset by the pulse of the signal g with a pulse @d equal to the signal width synchronized with the falling edge of the signal g.

As a result, a switching transistor drive signal indicated by signal i is obtained on the secondary side of the pulse transformer 7. Thereby, the switching transistor 10 is forcibly drawn to the negative voltage side at the time of turn-off, and the turn-off time can be shortened.

In this way, in this embodiment, the pulse transformer is reset immediately after the pulse width modulation signal by the reset signal having the same pulse width as the pulse width modulation signal. As a result, the voltage appearing on the secondary side of the pulse transformer is forcibly lowered to the negative voltage side and the turn-off time of the switching transistor is shortened, so that the power supply efficiency can be improved.

[Effects of the Invention] As explained above, the present invention applies a reset signal having the same pulse width as the pulse width modulation signal that excites the pulse transformer to the pulse transformer in synchronization with the falling edge of the pulse width modulation signal. The switching transistor drive signal appearing on the secondary side of the transformer can be forcibly dropped to the negative voltage side, and as a result, even if the pulse width is narrow, the switching transistor is reliably turned off immediately after the pulse falls. This has the effect of providing a switching transistor drive circuit that can improve power supply efficiency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a switching transistor drive circuit according to an embodiment of the present invention, FIG. 2 is a timing chart showing signals of each part in the switching transistor drive circuit of FIG. 1, and FIG. 3 is a conventional switching transistor drive circuit. FIG. 4 is a block diagram of the circuit and a timing chart showing signals of various parts in the switching transistor drive circuit of FIG. 3. l, 2: First and second sawtooth wave oscillators 3.4: First and second comparators 5.6: First and second pulse transformer excitation transistors 7: Pulse transformer 9: Synchronous signal generation circuit

Claims (2)

[Claims] (1) A pulse transformer and a pulse width that modulates the pulse width according to the control input, outputs an excitation pulse signal to the pulse transformer, and outputs a reset pulse signal immediately after the excitation pulse signal falls. A switching transistor drive circuit comprising: modulation means. (2) the pulse width modulation means performs pulse width modulation with a first sawtooth wave oscillator by comparing the control input with a sawtooth wave output from the first sawtooth wave oscillator;
a first comparator that outputs the reset pulse signal;
a synchronization signal generation circuit that detects the rising edge of the reset pulse signal and outputs a synchronization signal; and a synchronization signal generation circuit that detects the rise of the reset pulse signal and outputs a synchronization signal; a second comparator that performs pulse width modulation by comparing the generated second sawtooth wave oscillator with the control input and the sawtooth wave output from the second sawtooth wave oscillator, and outputs the excitation pulse signal; A switching transistor drive circuit according to claim 1, which has the following.