JP3050714B2 - Voltage resonance type power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer in which a resonance circuit is formed in a primary coil and a load circuit is connected to a secondary coil. The present invention relates to a voltage resonance type power supply circuit that adjusts and controls the voltage of a load circuit.

[0002]

2. Description of the Related Art FIG.
There is a circuit shown in

In the figure, Tr is a transformer,
A DC power supply VIN is connected to the secondary coil via a parallel circuit of a PNP transistor Q1 as a switching element and a capacitor C1, and a load circuit is connected to the secondary coil. D1 is a rectifying diode, L and C2 are smoothing reactors and capacitors, and D2 is a freewheeling diode. On the primary coil side, a resonance circuit is formed by the capacitor C1 and the coil of the transformer Tr.
OP1 is an amplifier which converts the output voltage VO on the load side into a resistor R1,
A predetermined voltage Vref1 is subtracted from the divided voltage obtained by dividing the voltage by R2, amplified, and a potential VOP1 is output. VCO2 is a voltage-controlled oscillator, and is a half cycle consisting of a period during which the potential VC1 of the capacitor C1 goes from 0 level to the next 0 level due to resonance, and a time from when the transistor Q1 is turned off to when it is turned on. And the transistor Q1 is turned on by adjusting the ON period in inverse proportion to the output voltage VO.
Control off.

FIG. 3 is a circuit diagram of a voltage controlled oscillator according to the present invention, and shows a circuit of the voltage controlled oscillator VCO2.
In the figure, OP2 is a comparator for turning on the transistor Q1, and OP3 is a comparator for turning off the transistor Q1. The comparator OP2 outputs a comparison reference voltage 2/3 VCC obtained by dividing the voltage VCC taken from the DC power supply VIN by each resistor R.
When the potential at the + terminal becomes equal to or higher than the comparison reference voltage, the flip-flop FF is reset, the output VFF via the amplifier AP is set to L level, and the transistor Q1 is turned on. The comparator OP3 receives the similarly divided reference reference voltage 1/3 VCC at its + terminal, sets the flip-flop FF when the potential of the-terminal becomes lower than the comparison reference voltage, and sets the output VFF to the H level. Transistor Q1
Off. C3 is a capacitor for applying a comparison control voltage to each of the comparators OP2 and OP3. Q2 is the capacitor C
A transistor that turns on and off the charging path for 3
When the flip-flop FF is set, the charging power supply VCC is turned on. R3 is a resistor that sets the charging time constant. Q3 is a transistor for turning on / off a discharge path to the capacitor C3, and turns on the discharge path when the flip-flop FF is reset.
R4 is a resistor for setting the discharge time constant. Q4
Is a transistor whose discharge time constant is increased or decreased according to the potential VOP1 based on the output voltage VO.

FIG. 4 is a voltage waveform diagram of each part of the voltage resonance type power supply circuit of FIG. At time t1, the potential VC3 of the capacitor C3 is 1/3 VCC, and the potential V
It is assumed that C1 has been discharged to the 0 level. At time t1
Sets the flip-flop FF and sets the transistor Q
Assuming that 1 changes from on to off, the potential VC3 increases with a predetermined charging time constant. At the same time, the capacitor C1
Potential VC1 rises and then starts to fall. When the potential VC3 reaches 2/3 VCC at time t2, the flip-flop FF is reset and the transistor Q1 turns on. At this time, a half cycle elapses and the potential VC1
Becomes 0 level. Thereafter, the potential VC3 drops with a discharge time constant inversely proportional to the output potential VOa of the amplifier OP1 adjusted based on the output voltage VO. When the potential VC3 reaches 1/3 VCC at time t3, the flip-flop FF is set. The transistor Q1 turns off. Therefore, the state becomes the same as at the time t1. Thereafter, similarly, when the output voltage VO is high, the 0-level period of the potential VC1 is relatively long, and when the output voltage VO is low, the period is adjusted to be short.

[0006]

However, in the above-described voltage resonance type power supply circuit, a half cycle of oscillation in the resonance circuit is made to coincide with a period in which the switching element of the resonance circuit is turned off by the voltage controlled oscillator. Therefore, there is a problem that the switching loss is increased and the conversion efficiency of the power supply is reduced because the switching element is turned on in a state other than zero potential between both ends of the switching element.

An object of the present invention is to provide a voltage resonance type power supply circuit having good conversion efficiency of a power supply by matching a half cycle of oscillation in a resonance circuit with a period during which a switching element of the resonance circuit is turned off. Is to do.

[0008]

According to the present invention, a DC power supply is connected to a primary coil of a transformer via a parallel circuit of a switching element and a capacitor, and a load circuit is connected to a secondary coil. A resonance circuit is formed on the primary coil side by a capacitor and a transformer coil, and the time from when the switching element is turned off to when the switching element is turned on is determined from the zero-level potential of resonance by the resonance circuit. 1/2 consisting of the period to reach the next zero level potential
In the voltage resonance type power supply circuit which substantially matches the cycle and controls the ON / OFF of the switching element by adjusting the ON period in inverse proportion to the voltage of the load circuit, the period during which the output is at a high level is shorter than the 1/2 cycle. A voltage-controlled oscillator that is set to a predetermined time and adjusts the low level period in inverse proportion to the voltage of the load circuit; and the potential at the connection point between the switching element and the primary coil is a potential corresponding to level 0, and A switching control circuit for controlling the switching element to be on during a period in which the potential of the output terminal of the control oscillator is at the potential corresponding to the low level.

[0009]

According to the present invention, when the potential of the output terminal of the voltage controlled oscillator becomes high level, the switching element is controlled to be turned off at that time, and thereafter, the potential of the connection point between the switching element and the primary coil becomes zero. When the potential is equivalent to the level and the potential at the output terminal of the voltage-controlled oscillator becomes low, the switching element is controlled to be turned on at that time and the on state is continued. The ON period is adjusted in inverse proportion to the voltage of the load circuit.

[0010]

FIG. 1 is a voltage resonance type power supply circuit diagram showing an embodiment of the present invention, and FIG. 5 is a voltage waveform diagram of each part thereof. In FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals, and different parts will be described below.

Q5 is an NPN transistor which forms a resonance circuit similar to the transistor Q1 in FIG. VCO1 is a voltage controlled oscillator. The circuit configuration is shown in FIG. 3 and is the same as that of the voltage controlled oscillator VCO2. Control oscillator VC
Different from O2. That is, the potential VC3 of the capacitor C3 is 1 /
The time from 3VCC to 2 / 3VCC is set to be sufficiently shorter than 1/2 cycle due to resonance of the resonance circuit, and accordingly, the time until the potential VC3 from 2 / 3VCC to 1 / 3VCC is set longer. Have been. D3 and D4 are diodes for superimposing the potential VC1 of the capacitor C1 in the resonance circuit and the output potential VFF of the voltage controlled oscillator VCO1.
Each potential is based on the 0 level, and the superimposed potential VT
Is at the 0 level when both the potential VC1 and the potential VFF are at the 0 level, and at the H level during periods other than the above conditions. OP
4 is a comparator for discriminating the 0 level with respect to the superimposed potential VT,
The comparison reference voltage is set slightly higher than the 0 level. When the superimposed potential VT is at the 0 level, the output potential VOP4 goes to the H level to turn on the transistor Q5. Level to turn off transistor Q5. The above diodes D3, D
4 and the comparator OP4 form a switching control circuit for switching-controlling the transistor Q5.

In the above configuration, it is assumed that the potential VC3 of the capacitor C3 is 1/3 VCC at time t1, and the potential VC1 of the capacitor C1 is discharged to the 0 level. If the flip-flop FF is set at the time t1 and the transistor Q5 shifts from on to off,
The potential VC3 increases with a predetermined charging time constant. At the same time, the potential VC1 of the capacitor C1 rises and then starts to fall. When the potential VC3 reaches 2/3 VCC at time t2, the flip-flop FF is reset and the potential VFF becomes 0 level. However, at this time, since the potential VC1 is not at the 0 level, the potential VOP4 is at the L level and the transistor Q5 remains off. Thereafter, the potential VC3 drops with a discharge time constant inversely proportional to the output potential VOa of the amplifier OP1 adjusted based on the output voltage VO. At the time t3, when a half cycle of the resonance elapses and the potential VC1 becomes 0 level, the potential VOP4 becomes H level and the transistor Q5 is turned on. Therefore, the point in time when the potential VC1 becomes 0 level and the point in time when the transistor Q5 is turned on surely coincide with each other. Thereafter, the potential VC3 drops with a discharge time constant inversely proportional to the output potential VOa of the amplifier OP1 adjusted based on the output voltage VO, and at time t4, the potential VC3 decreases by 1 /.
When the voltage reaches 3VCC, the flip-flop FF is set and the transistor Q5 is turned off. Therefore, the state becomes the same as that at the time t1, and the potential VC1 becomes 0 at the same time.
Ascend from level. Thereafter, similarly, when the output voltage VO is high, the 0-level period of the potential VC1 is relatively long,
When it is low, it is adjusted shortly to output a required constant voltage.

[0013]

As described above, according to the present invention, when the potential of the output terminal of the voltage controlled oscillator becomes high, the switching element is controlled to be turned off at that time, and thereafter, the switching element and the primary coil are connected. When the potential at the connection point is a potential corresponding to the 0 level and the potential at the output terminal of the voltage controlled oscillator goes to a low level, the switching element is controlled to be turned on at that time and the on state is continued. Therefore, the half cycle of the oscillation in the resonance circuit is matched with the period during which the switching element of the resonance circuit is turned off,
A voltage resonance type power supply circuit having good power supply conversion efficiency is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram of a voltage resonance type power supply circuit showing an embodiment of the present invention.

FIG. 2 is a diagram of a conventional voltage resonance type power supply circuit.

FIG. 3 is a circuit diagram of a voltage controlled oscillator according to the present invention.

FIG. 4 is a voltage waveform diagram of each part of the voltage resonance type power supply circuit of FIG. 2;

FIG. 5 is a voltage waveform diagram of each part of the voltage resonance type power supply circuit of FIG. 1;

[Explanation of symbols]

Tr: transformer, C1, C3: capacitor, Q1, Q2
, Q3, Q4, Q5 ... transistors, VCO1 ... voltage-controlled oscillator, R3 R4 ... resistors, OP2, OP3, OP4
... Comparator, FF ... Flip-flop, D3, D4 ... Diode.

Claims (1)

(57) [Claims] 1. A DC power supply is connected to a primary coil of a transformer via a parallel circuit of a switching element and a capacitor, and a load circuit is connected to a secondary coil. The primary coil side includes a capacitor and a coil of the transformer. A resonance circuit is formed, and the time from when the switching element is turned off to when the switching element is turned on is defined as a half of the period from the zero-level potential of resonance by the resonance circuit to the next zero-level potential.
In a voltage resonance type power supply circuit that controls the switching element on and off by adjusting the ON period in inverse proportion to the voltage of the load circuit so that the period substantially coincides with the period, the period during which the output is at a high level is shorter than the half period. A voltage-controlled oscillator that is set to a predetermined time and adjusts a low-level period in inverse proportion to the voltage of the load circuit; and a potential at a connection point between the switching element and the primary coil is a potential corresponding to level 0, and A switching control circuit that controls the switching element to be turned on during a period in which the potential of the output terminal of the control oscillator is at the potential corresponding to the low level.