JPH10225128A - Power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply wherein large reverse power is prevented from being applied to a switching device. SOLUTION: When a transistor Q1 is turned on, current is allowed to flow in a main inductance Tr1am of a primary windng Tr1a and the transistor Q1 from a smoothing DC power circuit 4 and then voltage is induced in a secondary winding Tr1b and then power is supplied to a lighting circuit 8. In the main inductance Tr1am, magnetic energy is accumulated. When the transistor Q1 is turned off, the magnetic energy accumulated in the main inductance Tr1am is transferred to a sub inductance Tr1as of a reverse phase and a resonance capacitor 4 and makes a free oscillation. As the main inductance Tr1am and the sub inductance Tr1as are 180 deg. out of, the voltage at the connection between the main inductance Tr1am and the sub inductance Tr1as, that is, the voltage divided by the main and the sub inductance Tr1am and Tr1as, is applied as reverse voltages to the filtred DC power circuit and the transistor Q1. The voltage to be applied to the transistor Q1 can be reduced by the sub inductance Tr1am.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for preventing a reverse voltage from being applied to switching means.

[0002]

2. Description of the Related Art Conventionally, as a power supply of this type, for example, a configuration described in Japanese Patent Application Laid-Open No. 8-78174 is known.

In the power supply described in Japanese Patent Application Laid-Open No. 8-78174, a full-wave rectification circuit is connected to a commercial AC power supply via a filter circuit, and a π-type circuit of a capacitor, a diode and a capacitor is connected to the full-wave rectification circuit. , Inductor,
A smoothing DC power supply circuit including a partial smoothing circuit having a capacitor and a diode is connected. Also, a series circuit of a parallel circuit of a capacitor and a transformer and a transistor is connected to the smoothed DC power supply circuit, and a fluorescent lamp is connected to a secondary winding of the transformer.

The DC voltage of the smoothing DC power supply circuit is turned on and off by a transistor. When the transistor is turned on, energy is stored in an inductance of a transformer and forcedly oscillates. When the transistor is turned off, the inductance and the capacitance of a capacitor cause parallel resonance. The fluorescent lamp is oscillated at a high frequency by free vibration, inducing a high frequency in the secondary winding of the transformer by the forced vibration and the free vibration.

[0005]

However, in the configuration described in Japanese Patent Application Laid-Open No. 8-78174, the resonance voltage generated in the parallel resonance circuit when the transistor is turned off is a reverse voltage between the smoothed DC power supply circuit and the transistor. Will be applied.

The reverse voltage is generated when the commercial AC power
When the voltage is 00 V, 1100 V or more is applied to the transistor, causing a large stress.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a power supply device that prevents a large reverse voltage from being applied to switching means.

[0008]

According to a first aspect of the present invention, there is provided a power supply device, wherein a parallel resonance circuit of an inductor and a capacitor and switching means connected in series to the parallel resonance circuit are connected in series to the power supply. In the power supply device, the parallel resonance circuit of the inductor and the capacitor is connected in parallel with the main inductor, and the sub-inductor and the capacitor having a phase opposite to the phase flowing through the main inductor are connected in series. And a series circuit connected to the power supply. Then, parallel resonance occurs in the parallel resonance circuit of the inductor and the capacitor, and the switching means performs a switching operation in accordance with the resonance voltage, and the combined impedance of the sub-inductor and the capacitor is formed in a leading phase opposite to the lagging phase of the main inductor. Therefore, when the switching means is turned on, a forced oscillating current flows from the power supply to the main inductor and the switching means, magnetic energy is stored in the main inductor, and when the switching means is turned off, the magnetic energy stored in the main inductor is reversed. The free oscillation that transfers to the sub-inductor and capacitor in phase occurs, and the main inductor and the sub-inductor are both lag components, and the resonance voltage generated at the connection point with the capacitor, which is the leading component, is Is applied as a partial pressure
The reverse voltage applied to the switching means is reduced.

According to a second aspect of the present invention, there is provided the power supply device according to the first aspect, further comprising a sub-capacitor connected in parallel to the sub-inductor and having a phase opposite to that of the capacitor when combined with the sub-inductor. Since the reverse voltage generated in the sub-inductor when the switching means is turned off is absorbed by the sub-capacitor, the reverse voltage applied to the switching means is further reduced.

According to a third aspect of the present invention, there is provided the power supply unit according to the first aspect, further comprising a diode connected in parallel with the sub-inductor and having a polarity short-circuited in a direction in which the main inductor is commutated. Therefore, when the electric charge charged in the main capacitor is discharged through the sub inductor and the main inductor, the vibration energy is the smallest.However, since the diode goes in the forward direction and short-circuits the sub inductor to reduce the impedance, it is free. The resonance vibration becomes smooth.

According to a fourth aspect of the present invention, in the power supply device according to any one of the first to third aspects, the main inductor and the sub inductor are magnetically coupled.
When the switching means is turned on, the magnetic energy is stored in the sub-inductor together with the main inductor, and when the switching means is turned off, the magnetic energy stored in the main inductor and the sub-inductor undergoes free oscillation to be transferred to the main capacitor having the opposite phase. As a result, the efficiency of storing magnetic energy is improved.

According to a fifth aspect of the present invention, in the power supply device according to any one of the first to fourth aspects, the main inductor and the sub-inductor are set such that the on-time and the off-time of the switching means are substantially equal. When the switching means is on, the inductance of the sub-inductor is reduced and the time constant is shortened. When the switching means is off, the time constant is set by the main inductor and the sub-inductor, whereby the switching means is switched. By setting the ON and OFF times to be constant, the DC component is prevented from flowing.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the power supply device of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a noise prevention circuit 1 is connected to a commercial AC power supply e, and the noise prevention circuit 1 has a full-wave rectifying means constituted by a bridge of diodes D1, D2, D3 and D4. An input terminal of the rectifier circuit 2 is connected. A first capacitor C1 having a relatively large capacity is connected to an output terminal of the full-wave rectifier circuit 2, and a diode D5 is connected in parallel with the first capacitor C1. A π type having a series circuit of a second capacitor C2 having a smaller capacity than the first capacitor C1 is formed.

A partial smoothing circuit 3 is connected to the second capacitor C2. The partial smoothing circuit 3 includes an inductor L1, a charging capacitor C3, and a first diode D6.
Are connected, and a second diode D7 is connected to a connection point between the inductor L1 and the first diode D6,
A smooth DC power supply circuit 4 as a DC power supply is configured.

Further, an inverter circuit 5 is connected to the smoothed DC power supply circuit 4. This inverter circuit 5 includes a primary winding Tr1a of a transformer Tr1 as an inductor.
And a parallel resonance circuit 6 of a resonance capacitor C4 as a capacitor. The primary winding Tr1a has a main inductor Tr1am for lag on one end side, and a combined impedance with the resonance capacitor C4 on the other end side. A sub-inductor Tr1as having a phase advance opposite to that described above is formed, and a smoothing DC power supply circuit 4 is connected to a connection point between the main inductor Tr1am and the sub-inductor Tr1as. The combined reactance of the resonance capacitor C4 and the sub inductor Tr1as is
The phase is set opposite to the main inductor Tr1am, that is, the phase is advanced. The collector and the emitter of the transistor Q1 serving as switching means are connected in series to the parallel resonance circuit 6. The base drive circuit 7 is connected to the base of the transistor Q1.

Furthermore, the secondary winding Tr1b of the transformer Tr1
Are connected to filaments FL1 and FL2 of a fluorescent lamp FL as a discharge lamp via a ballast L2. A starting capacitor C5 is connected to these filaments FL1 and FL2 to form a lighting circuit 8.

Next, the operation of the above embodiment will be described.

First, according to the simplified equivalent circuit shown in FIG.
In the parallel resonance circuit 6 of the inverter circuit 5, the transistor
When Q1 turns on, the transformer Tr
1, a current flows through the main inductor Tr1am of the primary winding Tr1a and the transistor Q1, and a voltage is induced in the secondary winding Tr1b of the transformer Tr1 to supply power to the lighting circuit 8, and magnetic energy is supplied to the main inductor Tr1am. Stored.

Next, when the transistor Q1 is turned off, the magnetic energy stored in the main inductor Tr1am undergoes free oscillation to be transferred to a series circuit with the sub-inductor Tr1as and the resonance capacitor C4 having opposite phases.

That is, the maximum vibration energy is obtained when the transistor Q1 is first turned off and the vibration is maximized.
And gradually decreases with the supply of energy to the load. When the transistor Q1 is turned off, the time constant is the same as the conventional case without the sub-inductor Tr1as because the inductance follows the inductance of both the main inductor Tr1am and the sub-inductor Tr1as during the free oscillation when the transistor Q1 is turned on. The time constant of the inductance of the sub-inductor Tr1as decreases according to the inductance of the main inductor Tr1am. Further, in the conventional case, the ON period of the transistor Q1 is longer than the OFF period, but the time constant can be changed between the forced vibration and the free vibration, and the duty ratio of the transistor Q1 can be changed.

The main inductor Tr1a, which is a slow component,
The voltage generated at the connection points a and c between the m and the sub-inductor Tr1as and the resonance capacitor C4, which is a leading component, is divided between a and b because the main inductor Tr1am and the sub-inductor Tr1as are in phase. The voltage is applied as a reverse voltage to the smoothing DC power supply circuit 4 and the transistor Q1, and the voltage applied to the transistor Q1 is reduced by the presence of the sub inductor Tr1am.

Here, a description will be given with reference to FIG. 1 by dividing into a section where the pulsating voltage of the full-wave rectifier circuit 2 of the smoothing DC power supply circuit 4 is higher than a charging voltage of the charging capacitor C3 and a section where the pulsating voltage is lower than the charging voltage.

First, when the transistor Q1 of the inverter circuit 5 is turned on at an arbitrary time in a section where the pulsating voltage of the full-wave rectifier circuit 2 is higher than the charging voltage of the charging capacitor C3, the primary winding Tr1a of the transformer Tr1 is turned on. Most of the current is supplied from the first capacitor C1, and part of the current is supplied from the second capacitor C2. The combined capacitance of the first capacitor C1 and the second capacitor C2 is sufficient to provide the energy required by the inverter circuit 5. In accordance with the current supply from the first capacitor C1 and the second capacitor C2, energy flows from the commercial AC power supply e side as an input current. In response to the change in the pulsating voltage, an operation is performed so as to accompany the switching operation of the transistor Q1, and the small and equal amplitude of the high frequency of the inverter operation of the inverter circuit 5 along the sine wave value of the AC voltage becomes full-wave. The voltage value of the rectifier circuit 2 is superimposed on all high sections.

That is, in a section where the voltage value of the full-wave rectifier circuit 2 is high, the first capacitor C1 and the second capacitor C2
Is a value in which the energy given by the supplied pulsating voltage is satisfied with respect to the energy required by the inverter circuit 5.

For this reason, both the first capacitor C1 and the second capacitor C2 have a small ripple component, a small amount of heat generation, and can improve the operation reliability.

Then, in a section where the voltage value of the full-wave rectifier circuit 2 is high, the charging capacitor C3 is charged when the transistor Q1 is turned on. Note that, in a section where the voltage value of the full-wave rectifier circuit 2 is high, the discharge is not performed from the charging capacitor C3 to the inverter circuit 5 side.

That is, when the transistor Q1 is turned on,
Inductor L1, charging capacitor C3, second diode
A current flows through the path of D7 and the transistor Q1, and the charging capacitor C3 is charged. Then, when the transistor Q1 is turned off, the magnetic energy stored in the inductor L1 causes a current to continue to flow through the inductor L1, so that a current flows through the path of the charging capacitor C3, the inductor L1, and the diode D8 to charge the charging capacitor C3. .

Next, in a section where the voltage value of the full-wave rectifier circuit 2 is low, when the pulsating sine wave voltage of the full-wave rectifier circuit 2 starts to decrease with respect to the charging voltage of the charging capacitor C3, the transistor Q1 is turned on. When turned on, the current to the inverter circuit 5 is first supplied from the second capacitor C2, and the current flows through the path of the second capacitor C2, the primary winding Tr1a of the transformer Tr1, and the transistor Q1. Then, at this time, as the ON amount of the transistor Q1 increases, the voltage of the second capacitor C2 decreases and becomes lower than the output voltage of the full-wave rectifier circuit 2, that is, the voltage of the first capacitor C1. 5 flows to the first capacitor C1, the secondary inductor Tr1as of the primary winding Tr1a of the transformer Tr1, the resonance capacitor C4 and the transistor Q1, and the fluorescent lamp FL
Supplied to

On the other hand, the release of energy of the charging voltage of the charging capacitor C3 is delayed due to the transient impedance of the inductor L1, and the energy is released immediately before the transistor Q1 is turned off. Then, when the transistor Q1 is turned off, the charging voltage of the inductor L1 becomes a power source, and the charging capacitor C
3. A current flows through the path of the second capacitor C2, the first diode D6 and the second capacitor C2 to charge the second capacitor C2, and the inductor L1 and the charging capacitor
Due to the resonance of C3, the voltage of the charging capacitor C3 is superimposed on the oscillation voltage. Here, since the inductor L1 and the second capacitor C2 are set so as to obtain an oscillating resonance, the charging of the second capacitor C2 is performed in a sine wave shape, and the maximum instantaneous voltage of the commercial AC power supply e is Both the portion and the portion of the lowest instantaneous voltage have substantially the same voltage value and are close to the DC voltage.

Here, a comparison experiment between the circuit shown in FIG. 1 and the conventional circuit will be described.

In the circuit shown in FIG.
F45 are connected in series, the effective voltage of the commercial AC power supply e is 200 V, the inductance of the primary winding Tr1a of the transformer Tr1 is 1.38 mH, and the resonance capacitor C4 is 8200p.
F, the number of turns of the sub-inductor Tr1as was set to 15% of the whole, and the conventional example in which the sub-inductor was not formed was used.

In the case of the conventional example, as shown in FIG. 8, the oscillation frequency is 43.5 kHz, the on time of the transistor Q1 is 13 μs, the off time is 10 μs, and the on duty is 56.5%.

The primary winding Tr of the conventional transformer Tr1
The voltage across 1a is equal to the reverse applied voltage of the transistor Q1, as shown in FIGS.
The voltage between both ends of the primary winding Tr1a of the transformer Tr1 is 280 times the smoothed DC power supply voltage from the reverse applied voltage of the transistor Q1.
The DC voltage of V is shifted. The transistor Q1
When the first diode D6 and the second diode are turned off
Since there is a current circulated by D7, the resonance voltage is rising, but this part is ignored.

As shown in FIG. 9, the lamp current flowing through the fluorescent lamp FL is 12.1 when the transistor Q1 is on.
4 μs, 10.6 μs when off, duty ratio 5
3.9%.

Then, the DC superposition ratio = (652−average value) / (652 − (− 532)) = 5.1%.

Further, lamp current crest factor = lamp current peak value / lamp current effective value = 652/358 = 1.82.

On the other hand, in the case of the above embodiment,
The oscillation frequency is 46.1 kHz, which is different from the conventional example in the resonance frequency of the sub inductor Tr1as, and the ON time of the transistor Q1 is 10.9 μs and the OFF time is 10.8 μs
And the on-duty is 50.2%.

As shown in FIGS. 3 to 5, the resonance voltage of the primary winding Tr1a of the transformer Tr1 is 1120 V,
The voltage of the main inductor Tr1am is 950V, and the reverse applied voltage of the transistor Q1 is 950V. Secondary inductor Tr
The voltage applied to 1as, the transistor compared to the conventional example
The reverse voltage applied to Q1 and the smoothing DC power supply circuit 4 is reduced, the withstand voltage of the transistor Q1 can be reduced, and electrical loss such as switching loss and conduction loss can be reduced. Further, sudden transients can be easily handled.

As shown in FIG. 6, the lamp current flowing through the fluorescent lamp FL is 11.1 when the transistor Q1 is on.
4 μs, 10.3 μs when off, duty ratio 5
The on-time and off-time of the transistor Q1 are approximately equal to those of the conventional example. However, since an LC system is included in addition to the resonance capacitor C4 and the transformer Tr1, the lamp current is as large as the duty ratio of the transistor Q1. Are not uniform.

Then, the DC superposition ratio = (608-average value) / (608-(-544)) = 2.8%, which is considerably smaller than the conventional 5.1%, and reduces the unbalance of the lamp current. In addition, the factors of cataphoresis and ground noise can be reduced.

Further, the lamp current crest factor = 608/349 = 1.74, which is considerably improved as compared with 1.82 of the conventional example, and the light output waveform can be improved.

In the above embodiment, the main inductor
Tr1am and the sub-inductor Tr1as are magnetically coupled, but may be separated from each other magnetically. Note that when magnetically coupled, when the transistor Q1 is turned on, the energy stored in the primary winding Tr1a is transferred to an opposite-phase resonance capacitor C4 when the transistor Q1 is turned off and freely oscillates. Storage efficiency is improved.

Next, another embodiment will be described with reference to FIG.

The embodiment shown in FIG. 10 differs from the embodiment shown in FIG. 1 in that a capacitor C6 as a sub-capacitor is connected in parallel with the sub-inductor Tr1as. It is sufficient that the capacitor C6 has such a size that commutation can be easily performed at the moment when the transistor Q1 is turned off.

The operation will be described with reference to an equivalent circuit shown in FIG. 11. In the parallel resonance circuit 6 of the inverter circuit 5, when the transistor Q1 is turned on, the main inductor of the primary winding Tr1a of the transformer Tr1 is supplied from the smoothing DC power supply circuit 4. Tr1a
A current flows through m and the transistor Q1, and a voltage is induced in the secondary winding Tr1b of the transformer Tr1 to supply power to the lighting circuit 8, and magnetic energy is accumulated in the main inductor Tr1am.

Next, when the transistor Q1 is turned off, the magnetic energy stored in the main inductor Tr1am is transferred to a series circuit of the sub-inductor Tr1as and the resonance capacitor C4 having opposite phases to charge the resonance capacitor C4 and perform free oscillation. . The back electromotive force generated in the sub inductor Tr1as at the moment when the transistor Q1 is turned off is absorbed by the capacitor C6.

Then, the voltage charged by the resonance capacitor C4 is discharged through the main inductor Tr1am and the sub inductor Tr1as, and returns to the initial state.

For other basic operations, see FIG.
This is the same as the embodiment shown in FIG.

Here, an experimental example of the circuit shown in FIG. 10 will be described.

In the circuit shown in FIG. 10, two HF45s are used in series for a fluorescent lamp, the effective voltage of the commercial AC power supply e is 200 V, the inductance of the primary winding Tr1a of the transformer Tr1 is 1.38 mH, and the resonance capacitor C4 is 8200
pF, the capacitor C6 is 1000pF, and the secondary inductor
The number of turns of Tr1as is 15% of the total, and the oscillation frequency is 4
This is 5.5 kHz.

Then, as shown in FIG. 12, the counter electromotive force generated at both ends of the sub-inductor Tr1as at the moment when the transistor Q1 is turned off is absorbed by the parallel circuit of the sub-inductor Tr1as and the sub-capacitor C6 by ringing of several cycles. Therefore, the resonance voltage of the main inductor Tr1as can be reduced from about 1120 V in the related art to about 900 V.

According to the above embodiment, the transistor Q1
The back electromotive force generated in the sub-inductor Tr1am at the time of turning off is absorbed by the capacitor C6, so that commutation becomes easy and free oscillation resonance can be performed smoothly. Therefore, the secondary inductor Tr
In the case of commutation when it is desired to greatly reduce the reverse voltage by increasing the inductance of 1as, it is possible to reliably prevent the oscillation from becoming unstable.

Next, another embodiment will be described with reference to FIG.

The embodiment shown in FIG. 13 is different from the embodiment shown in FIG. 1 in that a diode D8 is connected in parallel with the sub-inductor Tr1as in the direction of short-circuiting when the main inductor Tr1am is commutated. Things.

The operation will be described with reference to the equivalent circuit shown in FIG. 14. In the parallel resonance circuit 6 of the inverter circuit 5, when the transistor Q1 is turned on, the main inductor of the primary winding Tr1a of the transformer Tr1 is supplied from the smoothing DC power supply circuit 4. Tr1a
A current flows through m and the transistor Q1, and a voltage is induced in the secondary winding Tr1b of the transformer Tr1 to supply power to the lighting circuit 8, and magnetic energy is accumulated in the main inductor Tr1am.

Next, when the transistor Q1 is turned off, the magnetic energy stored in the main inductor Tr1am is transferred to a series circuit including the sub-inductor Tr1as and the resonance capacitor C4 to charge the resonance capacitor C4 and perform free oscillation.

At the moment when the transistor Q1 is turned off,
The back electromotive force generated in the secondary inductor Tr1as is
To absorb.

Then, the voltage charged by the resonance capacitor C4 is discharged via the main inductor Tr1am and the sub inductor Tr1as, and returns to the initial state.

FIG. 1 shows other basic operations.
This is the same as the embodiment shown in FIG.

The vibration energy is maximized when the parallel resonance circuit 6 is coupled and vibrates forcibly, and attenuates with the supply of energy to the lighting circuit 8 and the like. Therefore, the electric charge charged in the resonance capacitor C4 becomes the main inductor Tr1am
When discharging through the sub-inductor Tr1as, the vibration energy becomes the smallest and the impedance becomes relatively high.At this time, the sub-inductor Tr1as is short-circuited by the diode D8 and the impedance becomes low. Is performed smoothly.

Here, an experimental example of the circuit shown in FIG. 13 will be described.

In the circuit shown in FIG. 13, two fluorescent lamps HF45 are used in series, the effective voltage of the commercial AC power supply e is 200 V, the inductance of the primary winding Tr1a of the transformer Tr1 is 1.38 mH, and the resonance capacitor C4 is 8200
pF, and the number of turns of the secondary inductor Tr1as is 15% of the whole.
It operates at an oscillation frequency of 45.5 kHz.

Then, as shown in FIG. 15, the back electromotive force generated at both ends of the sub-inductor Tr1as at the moment when the transistor Q1 is turned off is absorbed by the diode D8.
Main inductor Tr1am voltage is about 1120V
To about 1000V. In this case, the voltage at which the back electromotive force can be reduced is smaller than in the embodiment shown in FIG. 10, but ringing hardly occurs.

According to the above embodiment, the transistor Q1
When the switch is off, the sub-inductor Tr1am is short-circuited by the diode D8, so that the impedance is reduced in the cycle in which the impedance is relatively high in the entire cycle, so that free oscillation resonance can be performed smoothly. Therefore, the secondary inductor
When commutation occurs when it is desired to greatly reduce the reverse voltage by increasing the inductance of Tr1as, it is possible to reliably prevent oscillation from becoming unstable.

In any of the embodiments, by making the on time and the off time of the transistor Q1 equal, the superposition of the DC component can be reduced, and the cataphoresis and the noise to the ground can be reduced.

[0067]

According to the power supply device of the first aspect, parallel resonance occurs in the parallel resonance circuit of the inductor and the capacitor,
The switching means performs a switching operation according to the resonance voltage, and the combined impedance of the sub-inductor and the capacitor is formed in a leading phase opposite in phase to the lagging phase of the main inductor. And a forced oscillating current flows through the switching means, magnetic energy is accumulated in the main inductor, and when the switching means is turned off, the magnetic energy accumulated in the main inductor causes free oscillation to be transferred to the sub-inductor and the capacitor in opposite phases, Both the main inductor and the sub-inductor are lag components, and the resonance voltage generated at the connection point with the capacitor, which is the leading component, is divided and applied to the main inductor and the sub-inductor. The reverse voltage to be applied can be reduced.

According to the power supply device of the second aspect, in addition to the power supply device of the first aspect, the reverse voltage generated in the sub-inductor when the switching means is turned off is absorbed by the sub-capacitor, so that the reverse voltage is applied to the switching means. The reverse voltage can be further reduced.

According to the power supply device of the third aspect, in addition to the power supply device of the first aspect, a diode having a polarity in a direction of short-circuiting in a direction in which the main inductor is commutated is connected in parallel with the auxiliary inductor. Therefore, when the electric charge charged in the main capacitor is discharged through the sub-inductor and the main inductor, the vibration energy is the smallest.However, since the diode is in the forward direction and the sub-inductor is short-circuited and the impedance is small, it is free. Resonance vibration can be made smooth.

According to the power supply device of the fourth aspect, in addition to the power supply device of any one of the first to third aspects, the main inductor and the sub-inductor are magnetically coupled, so that when the switching means is turned on. Magnetic energy is also stored in the sub-inductor together with the main inductor, and when the switching means is turned off, the magnetic energy stored in the main inductor and the sub-inductor undergoes free oscillation that transfers to the main capacitor of the opposite phase, so that the magnetic energy is stored. Efficiency can be improved.

According to the power supply device of the fifth aspect, in addition to the power supply device of any one of the first to fourth aspects, the main inductor and the sub-inductor may have inductances at a rate at which the on-time and off-time of the switching means are substantially equal. Is set, when the switching means is on, the inductance of the sub-inductor is reduced and the time constant is shortened. When the switching means is off, the time constant is set by the main inductor and the sub-inductor. By setting the ON and OFF times to be constant, it is possible to prevent a DC component from flowing.

[Brief description of the drawings]

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

FIG. 2 is an equivalent circuit diagram of FIG.

FIG. 3 is a waveform diagram showing a current of a transformer and a voltage across a primary winding of the transformer.

FIG. 4 is a waveform diagram showing a current of a transformer and a voltage between both ends of a main inductor.

FIG. 5 is a waveform chart showing a current of the transistor and a voltage across the transistor;

FIG. 6 is a waveform chart showing a lamp current according to the first embodiment;

FIG. 7 is a waveform diagram showing a current of a conventional transformer and a voltage across a main inductor.

FIG. 8 is a waveform chart showing a current of the transistor and a voltage across the transistor;

FIG. 9 is a waveform chart showing a lamp current according to the first embodiment;

FIG. 10 is a circuit diagram showing another embodiment of the power supply device of the present invention.

FIG. 11 is an equivalent circuit diagram of FIG. 10;

FIG. 12 is a waveform chart showing a current of a capacitor C6 and a voltage across a transformer.

FIG. 13 is a circuit diagram showing another embodiment of the present invention;

FIG. 14 is an equivalent circuit diagram of FIG. 13;

FIG. 15 is a waveform chart showing a current of a diode D8 and a voltage across a transformer.

[Explanation of symbols]

 4 Smoothing DC power supply circuit as power supply 6 Parallel resonance circuit C4 Resonant capacitor as capacitor C6 Capacitor as sub capacitor D8 Diode Q1 Transistor Tr1 as switching means Transformer as inductor Tr1am Main inductor Tr1as Secondary inductor

Claims (5)

[Claims] 1. A power supply device in which a parallel resonance circuit of an inductor and a capacitor and switching means connected in series to the parallel resonance circuit are connected in series to a power supply, wherein the parallel resonance circuit of the inductor and the capacitor is A main circuit, and a series circuit connected in parallel to the main inductor, and having a sub-inductor having a phase opposite to the phase flowing through the main inductor and the capacitor connected in series. And power supply. 2. A parallel connection with the sub inductor,
2. The power supply device according to claim 1, further comprising a sub-capacitor having a phase opposite to that of the capacitor when combined with the sub-inductor. 3. A parallel connection with the sub inductor,
2. The power supply device according to claim 1, further comprising a diode having a polarity in a direction of short-circuiting in a direction in which the main inductor is commutated. 4. The power supply device according to claim 1, wherein the main inductor and the sub inductor are magnetically coupled. 5. The power supply device according to claim 1, wherein the inductance of the main inductor and the sub-inductor is set so that the on-time and the off-time of the switching means are substantially equal.