JPH01318547A - Switching power source control system - Google Patents

Abstract

PURPOSE:To keep output voltage constant by bringing an output voltage control into a PWM control operated at a frequency f2 which is expressed by f2<<f1 where f1 is an oscillation frequency of a converter. CONSTITUTION:A switching power device is composed of a resonance type converter 1, a pulse width control circuit 2, a rectification circuit 3, an oscillator 4, a synchronous circuit 5 and a gate circuit 6. The resonance type converter 1 is operated at an oscillation frequency f1, where the ON-time or OFF-time is controlled. The pulse width control circuit 2 is operated at a frequency f2 where f2<<f1, keeping the output voltage constant to a load. By fixing this frequency f1, by PWM-controlling the operation of the converter 1 with a PWM control circuit 2 and by rectifying the current with a rectification circuit 3, the output can be kept at a constant voltage.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a switching power supply control system.

[Conventional technology]

Conventionally, there are two methods for controlling a resonant converter: one method is to control the operating time (on time) and frequency of the voltage converter, and the other is to control the non-operating time (off time) and frequency of the voltage converter.

[Problem to be solved by the invention]

Since the conventional control methods described above all use frequency control, the oscillation frequency changes in response to changes in the output current. As a result, noise at the oscillation frequency, that is, the fundamental frequency and its harmonics are generated in the entire frequency range to be controlled, and there is a problem that, for example, the noise overlaps with the sampling frequency of AD conversion, causing an error.

[Means to solve the problem]

The switching power supply control method of the present invention provides a feedback loop with a pulse width control circuit that operates at a frequency f2 with a relationship of f2<f with respect to the oscillation frequency f1 of a resonant converter that operates at an oscillation frequency f1, and The resonant converter is configured to operate so as to keep the output voltage to the load constant based on the output of the control circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

Referring to FIGS. 1 and 2 showing one embodiment, a resonant converter 1 operates at an oscillation frequency f1 and controls an on time or an off time. The pulse width control circuit (PWM control circuit) 2 operates at a frequency f2 such that f2<<f1, and keeps the output voltage to the load constant. Rectifier circuit 3 has frequency f2
The output of converter 1 is rectified. Oscillator 4 generates oscillation frequency f1 of converter 1. Synchronous circuit 5
is a circuit that synchronizes the frequencies f, , f2. Gate circuit 6 transmits an output of frequency f1 to converter 1 according to the output of PWM control circuit 2. Since the operation of the converter 1 is controlled by the on time or the off time, the converter 1 switches with zero current or zero voltage. Now, if the output current changes and the frequency is changed by 1 according to the change, the output of the rectifier circuit 3 will be made into a constant voltage, but here the frequency f1 is fixed and the PWM control circuit 2 By performing PWM control on the operation of step 1 using the waveform shown in FIG. 2 and rectifying it using the rectifier circuit 3, it becomes possible to make the output a constant voltage. FIG. 2 shows that a plurality of on/off pulses of the resonant converter 1 are generated in the on state of normal PWM control.

〔Effect of the invention〕

As explained above, according to the present invention, the output voltage control of the resonant converter is performed with respect to the oscillation frequency f of the converter.
By performing PWM control that operates at a frequency f2 where 2 < f t, only noise at a constant frequency is emitted in response to load current fluctuations, and frequency control that may have a negative impact on the load is avoided. be able to.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing one embodiment of the present invention.

Claims (1)

[Claims] A pulse width control circuit operating at a frequency f_2 having a relationship of f_2<<f_1 with respect to the oscillation frequency f_1 of a resonant converter operating at an oscillation frequency f_1 is provided in a feedback loop, and the output of the pulse width control circuit is output to a load. A switching power supply control method characterized in that the resonant converter is operated to keep the voltage constant.