JPH11146645A - Power supply equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss in a switching element and thereby increase efficiency of the power supply equipment, by extending the ON-state time of the switching element without changing the on-off duty ratio of it at stand-by load. SOLUTION: At the primary winding 6a side of a transformer 6, a winding 6d is installed. In the winding 6d, small voltage is induced when loads 17, 20 are large rated loads and large voltage is induced when these loads are small stand-by loads. When it is detected by a circuit constituted of a Zener diode 34 and resistors 33, 35 that large voltage is induced in the winding 6d, a switching transistor 44 is turned ON, and the resistance value of a circuit which determines the oscillation frequency of a PWM(pulse width modulation) control circuit 12 is increased, thereby lowering the oscillation frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a DC constant voltage power supply,
More specifically, the present invention relates to an intermittent control type power supply device.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional power supply device of an intermittent control system, that is, a so-called switching power supply, which uses an inverter control system and has two outputs. The input terminal of a full-wave rectifier circuit 5 composed of a diode bridge is connected to the AC power supply 1 via a power switch 2, a fuse 3, and a noise filter 4, and the output terminal of the full-wave rectifier circuit 5 is connected to a transformer 6 Primary winding 6a and switching element 7
And a first smoothing capacitor 8 is further connected in parallel to the series circuit of the primary winding 6a of the transformer 6 and the switching element 7. Further, a resonance capacitor 10 is connected to the primary winding 6a of the transformer 6 via a diode 9 with a reverse polarity, and a resistor 11 is connected to the resonance capacitor 10 in parallel.

The switching element 7 is a MOS (Meta)
l Oxide Semiconductor) A field effect transistor having a drain terminal connected to the primary winding 6a, a source terminal grounded, and a gate terminal connected to a PWM (Pulse Width).
Modulation) control circuit 12. A series circuit of a resistor 13 and a capacitor 14 is connected between the drain and source terminals.

The transformer 6 has the primary winding 6a wound on its primary side, and has a first secondary winding 6b-1 and this first secondary winding 6b-1 on its secondary side. Is wound around the second secondary winding 6b-2 having a different number of turns. Then, the first secondary winding 6
c-1 through the diode 15 to the second smoothing capacitor 1
6 and the voltage between the terminals of the second smoothing capacitor 16 is used as the supply voltage to the first load 17.
A third smoothing capacitor 19 is connected to the second secondary winding 6c-2 via a diode 18, and the voltage between the terminals of the third smoothing capacitor 19 is used as a supply voltage to the second load 20. Further, a stabilizing circuit 21 is connected in parallel to the third smoothing capacitor 19 so that the voltage detected by the stabilizing circuit 21 is fed back to the PWM control circuit 12 via a feedback circuit 22. Has become.

[0005] A tertiary winding 6 c is wound around the primary side of the transformer 6, and a fourth smoothing capacitor 24 is connected to the tertiary winding via a diode 23. The voltage between the terminals of the fourth smoothing capacitor 24 is applied to the PWM control circuit 12.

The PWM control circuit 12 includes a capacitor 2
5 is a drive circuit for controlling the switching operation of the switching element 7 at an oscillation frequency determined by a parallel circuit of the resistor 5 and the resistor 26. The drive circuit controls the voltage between the terminals of the fourth smoothing capacitor 24 and the feedback voltage from the feedback circuit 22. Based on this, the on / off duty ratio of the switching element 7 is variably controlled to stabilize the output voltage.

In this conventional device, when the PWM control circuit 12 performs high-frequency switching operation of the switching element 7 at a constant frequency, the resonance circuit of the primary winding 6a of the transformer 6 and the resonance capacitor 10 operates. Thus, a high-frequency voltage is generated in the primary winding 6a of the transformer 6. Thereby, the first and second secondary windings 6b-1 and 6b-2 also have one
A high-frequency voltage proportional to the turns ratio with respect to the next winding 6a is induced, and the second and third smoothing capacitors 16 and 19 are charged by this voltage. Then, the charging voltage (for example, +24 V) of the second smoothing capacitor 16 is applied to the first load 17.
, And the charging voltage (for example, +5 V) of the third smoothing capacitor 19 is provided as a power supply voltage to the second load 20.

The charging voltage of the third smoothing capacitor 19 is detected by the stabilizing circuit 21 and is fed back to the PWM control circuit 12 via the feedback circuit 22. Thereby, the switching element 7 can be
Is variably controlled to stabilize the output voltage.

In the conventional device having such a configuration, the gate voltage VG and the drain of the switching element 7 in a state where rated loads are connected as the first and second loads 17 and 20 (rated load state). FIG. 4A shows the waveform of the current ID. FIG. 4B shows the waveforms of the gate voltage VG and the drain current ID of the switching element 7 in a state where the minimum load is connected (standby load state).

As shown in the figure, in both the rated load state and the standby load state, the switching element 7 is turned on (gate voltage VG> GND level) at a constant cycle T,
It is repeatedly turned off (gate voltage VG = GND level). In the rated load state, the on-time (time during which current flows) of the switching element 7 is almost maximized (t0), and the energy transmitted at this time is small in the switching element 7 and the efficiency is high. Becomes On the other hand, in the standby load state, the switching element 7
Is reduced to a minimum (t1), and the energy transmitted at this time in the switching element 7 is large and the efficiency is low.

That is, the conventional device uses the switching element 7
Are designed in accordance with the rated load state, the response speed of the switching element 7 cannot follow the standby load state in which the ON time of the switching element 7 is reduced to the minimum. For this reason, as shown in the enlarged view of the part A in FIG. 5, loss currents k1 and k2 are generated before and after the switching element 7 is turned on, respectively, and energy corresponding to the loss currents k1 and k2 is generated by the switching element 7. The efficiency was poor because all the heat was lost at 7 and turned into heat.

[0012]

As described above, in this type of conventional power supply device, each element including the switching element 7 is designed in accordance with the rated load state, and is not affected by the load state. The switching speed of the switching element 7 cannot be followed during the standby load state in which the ON time of the switching element 7 is minimized. After that, there is a problem that the loss currents k1 and k2 are generated and the efficiency is reduced.

Therefore, the present invention extends the on-time of the switching element without changing the on / off duty ratio of the switching element in the standby load state, thereby reducing the loss in the switching element and improving the efficiency of the power supply device. The purpose is to aim.

[0014]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and achieves the object by providing a primary winding of a transformer and a switching element between output terminals of a rectifier circuit for rectifying an AC from an AC power supply. And a driving circuit for connecting a resonance capacitor in parallel with the primary winding of the transformer and for performing switching operation of the switching element at a constant frequency. A load state for detecting a magnitude of a load in a power supply device in which a resonance circuit including a primary winding and a resonance capacitor is operated and a resonance voltage transmitted to a secondary winding of a transformer is supplied to a load. A detecting means, and a frequency of a switching operation of the switching element controlled by the drive circuit based on the magnitude of the load detected by the detecting means. It is provided with a switching frequency varying means for varying a.

Here, the load state detecting means comprises a winding provided on the primary winding side of the transformer and a circuit for detecting a voltage generated in the winding. The switching frequency varying means changes the frequency of the switching operation in a direction to decrease when the load detected by the detecting means is small.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. 1 and 2 in which the present invention is applied to a switching power supply of an inverter control type and having two outputs. The same parts as those in FIGS. 3 and 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

That is, the power supply device (switching power supply) of the present embodiment shown in FIG. 1 is different from the conventional device shown in FIG. 3 in that a load state detection circuit 30 for detecting the sizes of the loads 17 and 20, A switching frequency variable circuit 40 that changes the frequency of the switching operation of the switching element 7 controlled by the PWM control circuit 12 based on the magnitude of the load detected by the load state detection circuit 30 is provided.

The load state detection circuit 30 includes a transformer 6
And a fifth smoothing capacitor connected via a diode 31 to the quaternary winding 6d wound in a direction opposite to the primary winding 6a and the tertiary winding 6c. 32,
The resistor 3 connected in parallel to the fifth smoothing capacitor 32
3 and a series circuit of a zener diode 34 and a resistor 35 having the illustrated polarity and connected in parallel with the resistor 33.

The switching frequency variable circuit 40 comprises:
Capacitor 41 connected in parallel to PWM control circuit 12
And a series resistor 4 connected in parallel with the capacitor 41.
2, 43 and a PNP connected in parallel with one resistor 43.
And a capacitor 45 connected in series to the base terminal of the switching transistor 44. The connection point between the base terminal of the switching transistor 44 and the capacitor 45 in the switching frequency variable circuit 40 and the Zener diode 34 in the load state detection circuit 30
And the connection point of the resistor 35 is short-circuited.

In the power supply device of the present embodiment having such a configuration, the switching transistor 44
Is ON (the base current is at the GND level), the oscillation frequency of the PWM control circuit 12 is
And the resistor 42. When the switching element 7 performs a high-frequency switching operation at this oscillation frequency, the primary winding 6a of the transformer 6 and the resonance capacitor 1
0 operates and the primary winding 6a of the transformer 6 operates.
Generates a high-frequency voltage. Thereby, the first and second 2
High-frequency voltages corresponding to the turn ratios with respect to the primary winding 6a are also induced in the secondary windings 6b-1 and 6b-2, and the second and third smoothing capacitors 16 and 19 are charged by this voltage. Then, the charging voltage of the second smoothing capacitor 16 is provided as a power supply voltage to the first load 17, and the charging voltage of the third smoothing capacitor 19 is provided as a power supply voltage to the second load 20.

The charging voltage of the third smoothing capacitor 19 is detected by the stabilizing circuit 21 and is fed back to the PWM control circuit 12 via the feedback circuit 22. Thus, the on / off duty ratio of the switching element 7 is variably controlled as needed, and the output voltage is stabilized.

Further, the first and second secondary windings 6b-1, 6b
The fourth winding 6d by the high-frequency voltage generated in each of b-2
Also, a high-frequency voltage proportional to the turns ratio is induced. When the high-frequency voltage induced in the fourth winding 6d reaches the breakdown voltage of the Zener diode 34, a reverse current flows through the Zener diode 34, the capacitor 45 is energized, and the switching transistor 44 is turned off. As a result, the oscillation frequency of the PWM control circuit 12 is determined by the capacitor 41 and the series resistors 42 and 43. That is, since the resistance value is higher than that when the switching transistor 44 is turned on, the oscillation frequency of the PWM control circuit 12 is reduced, and the switching operation of the switching element 7 is delayed.

Incidentally, the power supply device of the present embodiment
The output voltage V2 for the second load 20 of the output is feedback-controlled, and the output voltage V1 for the first load is not feedback-controlled. In this case, the output voltage V1 of the non-control system has a characteristic that depends on the fluctuation of the output voltage V2 of the control system. Therefore, the output voltage V2 of the control system is set to a voltage with small fluctuation (for example, +5 V), and the output voltage V1 of the non-control system is set to a voltage with large fluctuation (for example, +24 V). By doing so, the output voltage V1 of the non-control system is less affected by the fluctuation of the output voltage V2 of the control system, and the high-frequency voltage induced in the quaternary winding 6d is reduced by the load 17
When the output voltage V1 of the non-control system decreases due to an increase in the load 17, the output voltage V1 decreases in proportion to the decrease.
Rises in proportion to it.

Then, when the load 17 is in the standby load state where the load 17 is minimized, the high-frequency voltage induced in the quaternary winding 6d rises to the breakdown voltage of the Zener diode 34, the switching transistor 44 turns off, and the PWM control circuit The circuit is designed so that the oscillating frequency of Twelve drops to half.
Switching element 7 under rated load condition in this case
FIG. 2 shows the waveforms of the gate voltage VG and the drain current ID of FIG.
(A). FIG. 2 shows the waveforms of the gate voltage VG and the drain current ID of the switching element 7 in the standby load state.
(B).

As shown in the figure, in the rated load state, the switching element 7 is turned on (gate voltage VG> GND level) and off (gate voltage VG =
(GND level). At this time, the on-time of the switching element 7 has spread to almost the maximum (t0), and the transmitted energy
Loss is small and the efficiency is high.

On the other hand, in the standby load state, the switching element 7 is turned on (gate voltage VG> GND level) and turned off (gate voltage VG = GND level) twice as long as the cycle T in the rated load state. Repeat. However, the on / off duty ratio of the switching element 7 is the same as in the conventional standby load state. Therefore, although the on-time (t2) of the switching element 7 is narrow, it is twice as long as the on-time (t1) in the conventional standby load state, and the transmitted energy of the switching element 7 is small. The loss is smaller. As a result, efficiency in a standby load state can be improved, and power consumption during standby can be reduced.

In the above-described embodiment, the case where the frequency of the switching operation of the switching element 7 is changed in two stages between the standby load state and other times is described. Alternatively, the frequency of the switching operation may be changed stepwise in accordance with the detection.

In the above-described embodiment, the present invention is applied to a switching power supply of an inverter control type and having two outputs. However, the present invention is not limited to this. A load state detection circuit for detecting the magnitude of the load connected to the one output, and changing the frequency of the switching operation of the switching element controlled by the drive circuit based on the magnitude of the load detected by the detection circuit The present invention can be similarly applied by providing a switching frequency variable circuit that performs the switching.

[0029]

As described above in detail, according to the present invention, the on-time of the switching element can be extended without changing the on / off duty ratio of the switching element in the standby load state. Power loss can be reduced, efficiency can be improved, and power consumption during standby can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a power supply device according to an embodiment of the present invention.

FIG. 2 is a diagram showing voltage and current waveforms of the switching element in a rated load state and a standby load state in the embodiment.

FIG. 3 is a circuit configuration diagram of a conventional power supply device.

FIG. 4 is a diagram showing voltage and current waveforms of a conventional switching element in a rated load state and a standby load state.

FIG. 5 is an enlarged view of a portion A in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply 5 ... Full-wave rectifier circuit 6 ... Transformer 7 ... Switching element 10 ... Resonant capacitor 12 ... PWM control circuit 17, 20 ... First and second load 30 ... Load state detection circuit 40 ... Switching frequency variable circuit

Claims (3)

[Claims] 1. A series circuit of a primary winding of a transformer and a switching element is connected between output terminals of a rectifier circuit for rectifying an AC from an AC power supply, and is connected in parallel with the primary winding of the transformer. A drive circuit for connecting a resonance capacitor and performing a switching operation of the switching element at a constant frequency is provided, and a switching circuit of the switching element operates a resonance circuit between the primary winding of the transformer and the resonance capacitor. A power supply device that uses a resonance voltage transmitted to a secondary winding of the transformer as a supply voltage to a load; a load state detection unit that detects a magnitude of the load; A switching circuit that changes a frequency of a switching operation of the switching element that is controlled by the drive circuit based on the size; Power supply, characterized in that by comprising a number varying means. 2. The power supply according to claim 1, wherein the load state detecting means includes a winding provided on a primary winding side of the transformer, and a circuit for detecting a voltage generated in the winding. apparatus. 3. The power supply device according to claim 1, wherein the switching frequency varying means changes the frequency of the switching operation in a direction to decrease when the load detected by the detection means is small.