JPH04105416A - Switching transistor drive circuit - Google Patents

Abstract

PURPOSE:To drive a switching transistor(TR) in an on-time ratio over a wide range by modulating a pulse signal with a frequency sufficiently higher than a signal frequency by a pulse width control signal and passing this signal through a pulse transformer. CONSTITUTION:A PWM control circuit 1 compares a control signal (a) with a reference voltage (b) and outputs a pulse width modulation signal (c) of a frequency f1 having a pulse width Tp in response to a difference voltage. On the other hand, a rectangular wave oscillator 2 outputs a pulse signal (d) whose on-time ratio 50% and whose frequency is f2, and an inverting circuit 3 generates a pulse signal d' being the inverse of the pulse signal (d). The signals (d), d' are fed to AND circuits 4, 5, in which they are ANDed with a pulse width modulation signal (c). Since a pulse transformer 9 is designed to be operated at the frequency f2, for example, let f1 be 10kHz and f2 be 1kHz, then the switching TR is driven in an on-time ratio of 1-100% with respect to a conventional on-time ratio of 10-50%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching transistor drive circuit for a power supply, which is used in a power supply circuit such as a switching power supply, and requires insulation between a power supply control circuit and a switching transistor.

〔overview〕

In a switching transistor drive circuit having a pulse transformer that insulates a power supply control circuit and a switching transistor, the present invention modulates a pulse signal with a frequency sufficiently higher than the frequency of this signal using a pulse width control signal, and transmits this signal to the pulse transformer. By allowing the light to pass through, the switching transistor can be driven with a wide range of on-time ratios.

[Conventional technology]

Conventionally, in switching transistor drive circuits for power supplies that require insulation between the power supply control circuit (primary side) and the switching transistor (secondary side), a pulse transformer is used to transmit the switching transistor drive signal from the power supply control circuit to the switching transistor. When using this, there is an advantage that power can be supplied to the secondary side at the same time as the signal.

FIG. 3 shows an example of a switching transistor drive circuit using a conventional pulse transformer. 21 is a PWM control circuit, 22 is a transistor for driving a pulse transformer, 23 is a power supply for driving a switching transistor, 24 is a diode for resetting the pulse transformer, 25 is a pulse transformer for insulating the power supply control circuit and the switching transistor,
26 is a switching transistor. With this configuration, the PWM control circuit 21 does not perform pulse width modulation using the control signal. When the pulse width modulation signal is on, the primary winding of the pulse transformer 25 is excited.

On the other hand, when the pulse width modulation signal is in the OFF state, the pulse transformer 25 is reset by the pulse transformer reset diode 24 connected to the reset winding of the pulse transformer 25. In this way, the pulse waveform appearing on the secondary side of the pulse transformer 25 drives the switching transistor 26 with a switching waveform.

[Problem to be solved by the invention]

In switching transistor drive circuits using such conventional pulse transformers, due to limitations in the transfer characteristics of the pulse transformer, if the pulse width of the signal transmitted through the pulse transformer is narrow, the signal cannot be transmitted to the secondary side of the pulse transformer. The on-time ratio (ON duty) of the switching transistor per period is limited to at least about 10%. Further, due to the characteristics of the transformer, the maximum on-time ratio is 50%. This has the disadvantage that the variable range of the on-time ratio of the switching transistor becomes narrow.

The present invention solves these problems by reducing the on-time ratio to 10.
% or less and a switching transistor drive signal with an on-time ratio of 50% or more are transmitted to the secondary side of the pulse transformer, and the variable width of the on-time ratio of the switching transistor is wider than before. An object of the present invention is to provide a switching transistor drive circuit that can perform the following steps.

[Means to solve the problem]

The present invention includes a pulse width modulation control circuit that generates a pulse width modulation signal of a constant frequency having a pulse width corresponding to the difference between a control signal level and a reference level, and a signal equivalent to this pulse width modulation signal that is applied to a control electrode. In a switching transistor drive circuit including a pulse transformer inserted in a path between a given switching transistor and the pulse width modulation control circuit, the switching transistor drive circuit has a frequency sufficiently higher than that exhibited by the pulse width modulation signal generated by the pulse width modulation control circuit. a rectangular wave oscillator that oscillates a rectangular wave signal having a high frequency and an on-time ratio of approximately 50%; a pulse width modulation signal generated by the pulse width modulation control circuit; and a rectangular wave signal oscillated by the rectangular wave oscillator. and a first modulating means for generating a first signal by performing an AND operation on the pulse width modulation signal generated by the pulse width modulation control circuit and an inverted signal of the rectangular wave signal oscillated by the rectangular wave oscillator. a second modulating means for generating a second signal; a switching means for circulating a current that induces magnetic flux in the opposite direction to one coil of the pulse transformer; and a rectifier means for rectifying the voltage induced in the other coil of the pulse transformer and applying it to the control electrode of the switching transistor. It is characterized by having the following. Here, it is desired that the pulse transformer has a structure having sufficient specifications to allow a current having a frequency represented by a rectangular wave signal oscillated by the rectangular wave oscillator to flow back into its coil.

[Effect]

a pulse width modulated signal having a first frequency and a second frequency that is sufficiently higher than the first frequency;
A logical AND operation is performed with a pulse signal having an on-time ratio of substantially 50%, a pulse transformer that operates is driven by this signal, and the output of this pulse transformer is rectified and applied to the control electrode of the switching transistor. As a result, it is possible to transmit a pulse width modulation signal having a narrow pulse width by a multiple of the value of the ratio between the first frequency and the 20th frequency, and the on-time ratio of the pulse width modulation signal exceeds 50%. This pulse width modulated signal can be transmitted even if the

Absolute excuse: Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of this embodiment. cl is a p vv' xr control circuit that performs pulse width modulation at frequency f1;
3 is an inversion circuit that inverts the output pulse signal of the rectangular wave oscillator 2, and 4 and 5 are pulse width modulation output from the PWM control circuit 1. an AND circuit that takes the AND of the signal and the pulse signals output from the rectangular wave oscillator 2 and the inversion circuit 3; 6 and 7 are pulse transformer driving transistors driven by the output voltages of the AND circuits 4 and 5;
9 is a power supply for driving the switching transistor; 9 is a power supply for insulating the power supply control circuit and the switching transistor;
2 is a pulse transformer that operates; 10 is a bridge diode that rectifies the secondary pulse waveform of the pulse transformer; 11 is a bridge diode that rectifies the pulse waveform on the secondary side of the pulse transformer;
is a switching transistor. That is, this embodiment includes a PWM control circuit 1 that generates a pulse width modulation signal of a constant frequency having a pulse width corresponding to the difference between a control signal level and a reference level, and a signal equivalent to this pulse width modulation signal that is controlled. It is equipped with a pulse transformer 9 inserted in the path between the switching transistor 11 applied to the electrode and the PWM control circuit 1, and furthermore, as a feature of the present invention, the pulse width modulation signal generated by the PWM control circuit 1 is provided. The square wave oscillator 2 oscillates a square wave signal having a frequency sufficiently higher than that exhibited by the PWM control circuit 1 and the pulse width modulation signal generated by the PWM control circuit 1 and the square wave oscillator 2 oscillates. an AND circuit 4 which is a first modulation means that performs an AND operation with a rectangular wave signal to generate a first signal;
and an inversion circuit 3 which is a second modulation means that generates a second signal by performing an AND operation on the pulse width modulation signal generated by the PWM control circuit 1 and the inversion signal of the rectangular wave signal oscillated by the rectangular wave oscillator 2; A current that induces magnetic flux in opposite directions in the common magnetic path of the pulse transformer 9 according to the AND circuit 5, the first signal generated by the first modulation means, and the second signal generated by the second modulation means, respectively. pulse transformer driving transistors 6 and 7, which are switching means for circulating the voltage to one coil of the pulse transformer 9, and rectifying the voltage induced in the other coil of the pulse transformer 9 and applying it to the control electrode of the switching transistor 11. and a bridge diode 10 which is a means. Here, the pulse transformer 9 has a structure having sufficient specifications so that a current having the frequency exhibited by the rectangular wave signal oscillated by the rectangular wave oscillator 2 flows back into its coil.

Next, the operation of the switching transistor drive circuit having such a configuration will be explained with reference to the timing chart shown in FIG. 2.

In the PWM control circuit 1, the control signal a is compared with the reference voltage S, and the frequency f1 has a pulse width Tp according to the difference voltage.
A pulse width modulated signal C is output. On the other hand, the rectangular wave oscillator 2 outputs a pulse signal d having an on-time ratio of 50% and a frequency f2, and the inverting circuit 3 generates a pulse signal d' which is an inversion of the pulse signal d. The pulse signals d and d' are ANDed with the pulse width modulated signal C in AND circuits 4 and 5.

The pulse transformer 9 is excited via the pulse transformer driving transistors 6 and 7 by the signals e and e' obtained by AM modulating the pulse signals d and d' output from the AND circuits 4 and 5 with the pulse width modulation signal C. A signal f is transmitted to the secondary side of the pulse transformer. The signal f is rectified by a bridge diode 10 and demodulated into a switching transistor drive signal g equal to the pulse width modulated signal C;
The switching transistor 11 is driven.

In such an operation, the pulse transformer 9 is designed to operate at the frequency f2, so it has a lower frequency f1/ than the pulse transformer 25 in the conventional embodiment of FIG. A pulse width modulated signal C having a pulse width as narrow as f2 can be transmitted. On the other hand, even if the on-time ratio of the pulse width modulation signal C exceeds 50%, the pulse transformer 9 will be able to output the signal e with an on-time ratio of 50%.
and e', the pulse width modulated signal C can be transmitted without any problem.

As an example, f 1 = 10kHz, f 2 = 100
kHz, the on-time ratio that can be transmitted with conventional technology is 10% to 50%, but using the technology of the present invention, it is possible to drive a switching transistor with an on-time ratio of 1% to 100%. can.

〔Effect of the invention〕

As explained above, the present invention enables switching with a wide range of on-time VJ ratios by driving a pulse transformer with a signal obtained by AM modulating a pulse signal with a frequency f2 that is sufficiently larger than the frequency f1 using a pulse width control signal with a frequency f1. This has the effect of driving a transistor. Furthermore, by using a pulse transformer that operates at a frequency f2 that is higher than the frequency f1, there is an effect that the pulse transformer can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a diagram of an embodiment of the present invention. FIG. 2 is a timing chart showing signals of each part in FIG. 1. FIG. 3 is a block diagram of a conventional example. 1121... PWM control circuit, 2... Square wave oscillator, 3... Inversion circuit, 4.5... AND circuit, 6.7
．． 22... Pulse transformer driving transistor, 8.
23... Switching transistor driving power supply, 9.
25... Pulse transformer, 10... Bridge diode, 11.26... Switching transistor, 2
4... Diode for pulse transformer reset.

Claims (1)

[Claims] 1. A pulse width modulation control circuit that generates a constant frequency pulse width modulation signal having a pulse width corresponding to the difference between a control signal level and a reference level, and a signal equivalent to this pulse width modulation signal. in a switching transistor drive circuit comprising a pulse transformer inserted in a path between a switching transistor whose control electrode is given to the pulse width modulation control circuit and the pulse width modulation control circuit. a rectangular wave oscillator that oscillates a rectangular wave signal that has a frequency sufficiently higher than the frequency that the pulse width modulation control circuit generates and has an on-time ratio of approximately 50%, and a pulse width modulation signal generated by the pulse width modulation control circuit and the rectangular wave oscillator a first modulating means for generating a first signal by ANDing a rectangular wave signal; and an inverted signal of the pulse width modulation signal generated by the pulse width modulation control circuit and the rectangular wave signal oscillated by the rectangular wave oscillator. a second modulating means for generating a second signal by performing an AND operation on the pulse transformer; a switching means for circulating a current that induces magnetic flux in the opposite direction in a common magnetic path to one coil of the pulse transformer; and a switching means for rectifying the voltage induced in the other coil of the pulse transformer to a control electrode of the switching transistor. 1. A switching transistor drive circuit comprising: rectifying means for providing a switching transistor. 2. Patent claim 1, wherein the pulse transformer has a structure having sufficient specifications so that a current having a frequency exhibited by a rectangular wave signal oscillated by the rectangular wave oscillator flows back into its coil.
The switching transistor drive circuit described.