JPH02311168A - Pulse width control current resonance converter - Google Patents

Abstract

PURPOSE:To prevent mutual interference between a plurality of converters during parallel operation by varying the capacitance of a resonance capacitor automatically according to the variation of output voltage. CONSTITUTION:Control circuit 13 for a switching circuit 6 raises the gate voltage of a switching transistor 12 with preset period T and switches the source- drain of a transistor 19 to ON state. Consequently, sinusoidal current flows through a coil 8. A current detector 12 detects zero reset timing of the resonance current and pulls down the output voltage from a control circuit 13. A waveform having low duty ratio is obtained under a state where the resonance frequency of resonance circuit is high while a waveform having low duty ratio is obtained under a state where the resonance frequency is low. Output voltage from a smoothing circuit varies according to the value of the duty ratio, and reset 4 to a predetermined level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulse width controlled current resonant converter.

[Conventional technology]

Conventional current resonant converters control output voltage using a frequency control method. In other words, a sinusoidal half-wave current is obtained by switching a DC power supply to a resonant circuit consisting of a coil and a capacitor, but the length of time that the switching is on is a constant value determined by the resonant frequency of the resonant circuit. By controlling the length of time that the switching is in the off state, the duty ratio, that is, the ratio of the on time to the switching period, is changed to variably control the output voltage.

[Problem to be solved by the invention]

In the conventional current resonant converter described above, the resonant frequency of the resonant circuit is a constant value, and the switching duty ratio must be changed in order to variably control the output voltage. There is a problem in that the switching periods of the circuits become irregular and the combined output voltage changes in a beat-like manner and becomes unstable.

[Means to solve the problem]

The converter of the present invention has a resonant circuit in which a coil and a capacitor are connected in series, and a connection between the resonant circuit and a DC power source, which is turned on at predetermined intervals, and in response to this, the current flowing through the resonant circuit is turned on. a switch circuit that switches the connection to an off state when the voltage returns to zero; a smoothing circuit that smoothes and outputs the voltage across the capacitor; and a control circuit that generates a control signal indicating the magnitude of the output voltage of the smoothing circuit. The mirror circuit is connected to both ends of the capacitor and varies the equivalent capacitance at both ends of the capacitor in response to the control signal.

〔Example〕

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

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

An input capacitor 5 is connected between input terminals 1 and 2, and a coil 8 and a mirror circuit 14 are connected via a switching circuit 6.
A resonant circuit consisting of a capacitor 9 is connected to the resonant circuit. Capacitor 9 is diode 7 for flywheel
are connected in parallel, and both ends thereof are connected to output terminals 3 and 4 via a smoothing circuit consisting of a coil 10 and a capacitor 11. The resonance capacitor 9 is connected between the base and collector of the transistor 16 in the mirror circuit 14. A voltage-driven current source 17 and a DC power source 1 are connected between the emitter and collector of the transistor 16.
8 are connected in series. If the mutual conductance of the transistor 16 is g, then a capacitor C is connected to the resonant circuit.
This is equivalent to connecting a capacitor with twice the capacitance of g of 9, and the mutual conductance g is equal to that of transistor 1.
6 varies depending on the magnitude of the collector current. Therefore,
By changing the supply current from the current source 17, the equivalent capacitance of the capacitor can be changed and the resonant frequency of the resonant circuit can be changed.

As shown in FIG. 2, the control circuit 13 of the switching circuit 6 raises the gate voltage of the switching transistor 12 at preset intervals T (time tfl), and turns on the source-drain of the transistor 19. Switch to state. In response, a sinusoidal resonant current flows through the coil 8. The current detector 12 detects the timing at which this resonant current returns to zero, and causes the output voltage of the control circuit 13 to fall (time trt or t, 2). When the resonant frequency of the resonant circuit is high, a waveform with a low duty ratio is obtained, as shown by the solid line in Figure 2, and conversely, when the resonant frequency is low, the duty ratio is low, as shown by the broken line in Figure 2. A waveform with a high ratio can be obtained.

The output voltage of the smoothing circuit changes up or down depending on the level of the duty ratio.

When the output voltage of the smoothing circuit becomes higher (or lower) than the desired value, the error voltage is amplified by the error amplifier 15, and the amplified output voltage is applied to the current source 17 to reduce (or reduce) the collector current of the transistor 16. By increasing (or increasing) the resonant capacitance and increasing (or decreasing) the resonant frequency, the output voltage is automatically adjusted to lower (or increase) and the output voltage returns to the desired value. let

In this way, by variably controlling the capacitance of the resonant capacitor and variably controlling the resonant frequency, the switching duty ratio can be varied while keeping the switching period constant, realizing pulse width control type operation. can. As a result, even if multiple units are operated in parallel, the output voltage will not become unstable as in conventional circuits.

〔Effect of the invention〕

As explained above, the present invention enables pulse width control with a constant frequency by automatically changing the capacitance value of the resonance capacitor according to changes in the output voltage, and enables parallel operation of multiple converters. This has the effect of preventing mutual interference.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram illustrating the operation of the embodiment of the present invention.

1.2...Input terminal, 3,4...Output terminal, 5.9
゜11... Capacitor, 6... Switch circuit, 7.
...Diode, 8, 10... Coil, 12... Current detector, 13... Control circuit, 14... Mirror circuit, 15... Error amplifier, 16... Transistor, 1
7... Current source, 18... DC power supply.

Claims (1)

[Claims] A resonant circuit in which a coil and a capacitor are connected in series, and a connection between the resonant circuit and a DC power source are turned on at preset intervals, and in response, when the current flowing through the resonant circuit returns to zero, the a switch circuit for switching the connection to an OFF state; a smoothing circuit for smoothing and outputting the voltage across the capacitor; a control circuit for generating a control signal indicating the magnitude of the output voltage of the smoothing circuit; and a control circuit connected to both ends of the capacitor. and a mirror circuit that varies the equivalent capacitance at both ends of the capacitor in response to the control signal.