JP2000245160A - Power supply equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply equipment wherein lower voltage is applied to a switching element with no increase in a switching loss. SOLUTION: Between DC output terminals of a rectifier DB, a smoothing capacitor CO is connected through a parallel circuit of a capacitor C2 and a diode D1. Between both terminals of the smoothing capacitor C0, a series circuit of switching elements Q1, Q2 which are alternately turned on and off at high frequencies is connected via a parallel circuit of a capacitor C3 and a diode D2, A primary winding of a transformer T1 is connected to a connection between a high potential side DC output terminal of the rectifier DB and a connection between the switching elements Q1, Q2. A load circuit 1 with a discharge lamp FL is connected to a secondary winding of the transformer T1. The electrostatic capacity of the capacitor C3 is set to such a value, that a half cycle of the resonance voltage of the capacitor C3 near a peak of the AC supply voltage is substantially the same as an on-state period of the switching element Q1.

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 converting a DC voltage obtained by rectifying and smoothing a power supply voltage of an AC power supply into a high-frequency voltage and supplying the high-frequency voltage to a load.

[0002]

2. Description of the Related Art As a power supply device of this kind, the present inventors have proposed a power supply device having a circuit having a configuration as shown in FIG. This power supply device includes a rectifier DB for full-wave rectification of a power supply voltage of an AC power supply AC, a smoothing capacitor C0 connected between a DC output terminal of the rectifier DB via a parallel circuit of a diode D1 and a capacitor C2, and a smoothing capacitor C0. A series circuit of switching elements Q1 and Q2 composed of MOSFETs connected between both ends of a capacitor C0 via a parallel circuit of a diode D2 and a capacitor C3, and a DC output terminal on the high potential side of the rectifier DB and the switching elements Q1 and Q2. A transformer T1 composed of a leakage transformer having a primary winding connected to a connection point, a load circuit 1 connected between both ends of a secondary winding of the transformer T1, a switching element Q1,
Q2 is turned on / off alternately at a frequency sufficiently higher than the power supply frequency.
And a control circuit 2 for turning off. Here, the load circuit 1 includes a discharge lamp FL composed of a fluorescent lamp in which the power supply terminals of both filament electrodes are connected between both ends of the secondary winding of the transformer T1, and a non-power supply terminal of both filament electrodes of the discharge lamp FL. Preheating and resonance capacitor C connected between
1 and a resonance circuit is configured by the leakage inductance of the transformer T1 and the capacitor C1 (for example, see Japanese Patent Application Laid-Open No. 10-285946).

The operation of this circuit in a steady state will be briefly described with reference to waveform diagrams shown in FIGS. Here, FIGS. 8A and 8B show the switching element Q
8 (c) is a waveform diagram of the current IT1 flowing through the primary winding of the transformer T1, and FIGS. 8 (d) and (e) are switching devices Q1 and Q2. 8 (f) and 8 (g) show the waveforms of the currents IQ1 and IQ2 flowing through the capacitors C2 and C3.
2 and Vc3, and FIG. 8H is a waveform diagram of the input current Iin from the AC power supply AC.

In the steady state, the smoothing capacitor C0 is charged, so when the switching element Q2 is turned on, the smoothing capacitor C0 → the capacitor C2 → the primary winding of the transformer T1 → the switching element Q2 → the smoothing capacitor C0. Discharge current flows from the smoothing capacitor C0 through the path, and power is supplied to the load circuit 1 while charging the capacitor C2 (period Ta in FIG. 8). Then, FIG.
As shown in (f), the voltage Vc2 across the capacitor C2 is obtained.
Is the voltage Vdc across the smoothing capacitor C0 and the rectifier D
B (= Vdc− | Vs)
|), A current flows through the path of AC power supply AC → rectifier DB → primary winding of transformer T1 → switching element Q2 → rectifier DB → AC power supply AC, and AC power supply A
The input current Iin is drawn from C (period T in FIG. 8).
b).

Next, when the switching element Q2 is turned off, the energy stored in the transformer T1 when the switching element Q2 is turned on uses the AC power supply AC → the rectifier D
B → the primary winding of the transformer T1 → parasitic diode (not shown) of the switching element Q1 → capacitor C3 → smoothing capacitor C0 → rectifier DB → current flows through the path of the AC power supply AC, and the input current Iin from the AC power supply AC. While being pulled in, the smoothing capacitor C0 and the capacitor C3 are charged (period Tc in FIG. 8). In this period, as shown in FIG. 8 (g), the voltage Vc3 across the capacitor C3 increases due to the resonance action with the leakage inductance of the transformer T1.

Thereafter, when the switching element Q1 is turned on, the leakage inductance of the transformer T1 and the resonance action of the capacitors C1, C2 and C3 cause the capacitor C2 → the capacitor C3 → the switching element Q1 → the primary winding of the transformer T1 → the capacitor. The resonance current flows through the path of C2, and the voltages Vc2 and Vc across the capacitors C2 and C3.
3 changes from increasing to decreasing, and these energies are supplied to the load circuit 1 via the transformer T1 (period T3 in FIG. 8).
d). At this time, the direction of the current flowing through the primary winding of the transformer T1 is opposite to the direction of the current when the switching element Q2 is turned on, so that an alternating high-frequency voltage can be applied to the load circuit 1.

Next, when the switching element Q1 is turned off, the energy stored in the primary winding of the transformer T1 is released when the switching element Q1 is turned on, and the primary winding of the transformer T1 → the capacitor C2 → the smoothing capacitor C
0 → a parasitic diode of the switching element Q2 (not shown) → a current flows through the path of the primary winding of the transformer T1 (period Te in FIG. 8). If the voltages Vc2 and Vc3 across the capacitors C2 and C3 become zero during these periods, the diodes D1 and D2 connected in parallel to the capacitors C2 and C3 conduct, and the current continues to flow.

When the energy stored in the transformer T1 is released in this state, the state returns to the state where the current is discharged from the smoothing capacitor C0 (period Ta in FIG. 8), and the above-described series of operations are repeated to load the load. Alternating high frequency power is supplied to the circuit 1. 8A to 8H, while the switching elements Q1 and Q2 are repeatedly turned on and off once, the input current I
There is a period during which in is pulled. The switching frequency of the switching elements Q1 and Q2 is set to a high frequency such that the power supply voltage Vs of the AC power supply AC can be regarded as substantially constant during one cycle in which the switching elements Q1 and Q2 are turned on and off.

By performing the above operation, the operation waveform of each part of the circuit changes during one cycle of the power supply voltage Vs of the AC power supply AC as shown in FIGS. 9 (a) to 9 (f). FIGS. 9A and 9B are waveform diagrams of the voltages Vc2 and Vc3 across the capacitors C2 and C3, and FIG.
FIG. 9 is a waveform diagram of the voltage VT1 applied to the primary winding of FIG.
9D is a waveform diagram of the current IT1 flowing through the primary winding of the transformer T1, and FIG. 9E is an input current Ii from the AC power supply AC.
9 (g) is a waveform diagram of the lamp current Ila flowing through the discharge lamp FL.

As shown in FIGS. 9A to 9F, the voltage Vc2 across the capacitor C2 decreases as the power supply voltage Vs of the AC power supply AC increases, whereas the voltage Vc3 across the capacitor C3 decreases. Changes according to the power supply voltage Vs of the AC power supply AC. In the primary winding of the transformer T1,
Since the voltage of the sum of the voltages Vc2 and Vc3 across the capacitors C2 and C3 is applied, the voltage VT1 applied to the primary winding of the transformer T1 should be substantially constant as shown in FIG. As a result, the crest factor of the current Ila flowing through the load (discharge lamp FL) connected to the secondary side of the transformer T1 can be reduced. Further, the switching elements Q1,
The series circuit of Q2 includes a voltage V across the smoothing capacitor C0.
Since the operation is performed using the voltage obtained by adding the voltage Vc3 across the capacitor C3 to dc, the voltage Vdc across the smoothing capacitor C0 can be reduced. Further, since the voltage Vc3 across the capacitor C3 increases in a resonant manner, the voltage Vc3 shown in FIG.
As shown in (b), the voltage at the moment when the switching element Q2 is turned off is substantially equal to the voltage Vdc across the smoothing capacitor C0, and the voltage Vdc across the smoothing capacitor C0.
The switching loss of switching elements Q1 and Q2 can be reduced by an amount that can reduce dc.

Although not shown in FIG. 1, in a power supply device for supplying this kind of high-frequency power to the load circuit 1, in order to prevent high-frequency components from being mixed into the AC power supply AC side, It is common practice to insert a filter circuit for blocking high-frequency components between the power supply AC and the rectifier DB. By providing such a filter circuit, the input current Iin from the AC power supply AC is provided.
Only the envelope component of the input current Iin as shown in FIG. 9E is extracted, and an input current substantially proportional to the power supply voltage Vs of the AC power supply AC is obtained. Here, the current waveform of the input current Iin from the AC power supply AC greatly changes depending on the capacitance of the capacitor C2. For example, the capacitor C2
When the amplitude of the voltage Vc2 between both ends increases,
As shown in (a), during the period when the input current Iin flows from the AC power supply AC to the filter circuit, the polarity is inverted and large noise is generated. When the amplitude of the voltage Vc2 across the capacitor C2 decreases, a pause occurs in the input current Iin flowing from the AC power supply AC to the filter circuit, as shown in FIG. 10C. In any case, high-frequency noise is mixed into the AC power supply AC. Therefore, by setting the capacitance value of the capacitor C2 so that the input current Iin has a current waveform as shown in FIG. 10B, The harmonic distortion of the input current Iin can be reduced, and the input power factor can be improved.

[0012]

In the power supply device having the above-described structure, the sum of the voltage across the smoothing capacitor C0 and the voltage across the capacitor C3 is applied to the switching element Q2, and the voltage applied to the switching element Q2 is an alternating current. It becomes maximum near the peak value of the power supply voltage of the power supply AC. here,
When the capacitance value of the capacitor C3 is small, the amplitude of the voltage between both ends of the capacitor C3 becomes large. Therefore, it is necessary to use an element having a high withstand voltage as the switching element Q2, and there is a problem that the cost is increased. On the other hand, when the capacitance value of the capacitor C3 is large, the amplitude of the voltage between both ends of the capacitor C3 becomes small. Therefore, the switching element Q1 is turned off before the voltage between both ends of the capacitor C3 becomes 0 V, and the switching element Q1 is turned on. The voltage applied to the switching element Q2 at the time of switching from to OFF was increased. Thereafter, even when the switching element Q1 switches from off to on, the voltage at which the switching element Q1 switches from on to off is applied to the switching element Q2, so that there is a problem that switching loss increases and circuit efficiency decreases. Was.

The present invention has been made in view of the above problems, and has as its object to reduce the harmonics contained in the input current, reduce the voltage across the smoothing capacitor, and reduce the load current. It is an object of the present invention to provide a power supply device having a small crest factor, in which a switching element having a low withstand voltage can be used without increasing switching loss.

[0014]

According to one aspect of the present invention, there is provided a rectifier for rectifying a power supply voltage of an AC power supply, a smoothing capacitor for smoothing a rectified voltage of the rectifier, and a smoothing capacitor. A series circuit of first and second switching means connected in parallel and alternately turned on and off at a high frequency; first and second rectifiers connected in antiparallel to the first and second switching means, respectively; A transformer having a primary winding connected between a connection point of the first and second switching means and one DC output terminal of the rectifier; a load circuit connected to a secondary winding of the transformer; A parallel circuit of a first capacitor and a third rectifier having one end connected to a connection point between the winding and one DC output terminal of the rectifier and having the other end connected to one terminal of the smoothing capacitor; No. Capacitor and a third rectifying means of the parallel circuit and the connection point between the first and second and the smoothing capacitor
Connected between the switching means and the series circuit.
And a parallel circuit of fourth rectifier means.
The second period is set such that the half period of the resonance voltage applied to the second capacitor near the peak value of the power supply voltage of the AC power supply is substantially equal to the ON period of the first or second switching means.
The capacitance of the capacitor is set,
When one of the first and second switching elements whose one end is connected to the second capacitor is turned on, the voltage across the smoothing capacitor and the both ends of the second capacitor are applied across the other switching element. A voltage equal to the sum of the voltages is applied. The static voltage of the second capacitor is set so that the half period of the resonance voltage of the second capacitor is substantially equal to the ON period of the first or second switching element. Since the capacitance is set, the amplitude of the resonance voltage of the second capacitor can be made smaller than when the half cycle of the resonance voltage is shorter than the ON period, and when one of the switching elements is turned off. Since all the charges accumulated in the second capacitor are discharged, the second capacitor at the time when one of the switching elements switches from on to off or from off to on. The voltage applied to the other switching element can be made substantially equal to the voltage applied to the both ends of the smoothing capacitor, and the peak value of the voltage applied to the switching element can be reduced without increasing the switching loss. Can be reduced.

According to the second aspect of the present invention, a rectifier for rectifying a power supply voltage of an AC power supply, a smoothing capacitor for smoothing a rectified voltage of the rectifier, and a first capacitor connected in parallel with the smoothing capacitor and alternately turned on and off at a high frequency. And a series circuit of the second switching means, first and second rectification means connected in anti-parallel to the first and second switching means, respectively, and a connection point between the first and second switching means and the rectifier. A transformer having a primary winding connected to one of the DC output terminals, a load circuit connected to a secondary winding of the transformer, a first capacitor connected between the DC output terminals of the rectifier,
A third rectifier having one end connected to a connection point between the primary winding of the transformer and one DC output terminal of the rectifier and having the other end connected to one terminal of the smoothing capacitor;
And a parallel circuit of a second capacitor and a fourth rectifier connected between a connection point of the rectifier and the smoothing capacitor and a series circuit of the first and second switching means. The half period of the resonance voltage applied to the second capacitor near the peak value of the power supply voltage is substantially equal to the ON period of the first or second switching means.
The capacitance of the second capacitor is set, and one end of the first and second switching elements is connected to the second capacitor.
When one switching element connected to the capacitor is turned on, the sum of the voltage across the smoothing capacitor and the voltage across the second capacitor is applied across the other switching element. Since the capacitance of the second capacitor is set such that the half period of the resonance voltage of the second capacitor is substantially equal to the ON period of the first or second switching element, the half period of the resonance voltage is The amplitude of the resonance voltage of the second capacitor can be reduced as compared with the case where it is shorter than the ON period, and when one of the switching elements is turned off, all the electric charges accumulated in the second capacitor are discharged. Therefore, the voltage across the second capacitor when one of the switching elements switches from on to off or from off to on becomes substantially zero,
The voltage applied to the other switching element can be made substantially equal to the voltage across the smoothing capacitor, and the peak value of the voltage applied to the switching element can be reduced without increasing the switching loss.

According to a third aspect of the present invention, in the first or second aspect of the present invention, a capacitance changing means for changing the capacitance of the second capacitor is provided. Even if the on-period of the switching element changes as in the case of changing the switching frequency or on-duty of the switching element in accordance with the fluctuation, the capacitance variable means changes the power supply voltage of the AC power supply in accordance with the change of the on-period. Changing the capacitance of the second capacitor so that the half period of the resonance voltage applied to the second capacitor near the peak value is substantially equal to the ON period of the first or second switching means. Claim 1 or 2
As in the invention of the first aspect, the peak value of the voltage applied to the switching element can be reduced without increasing the switching loss.

[0017]

Embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a circuit diagram of a power supply device according to this embodiment. This power supply device includes a rectifier DB for full-wave rectification of a power supply voltage of an AC power supply AC, a diode D1 as a third rectifier between a DC output terminal of the rectifier DB, and a first rectifier.
And a smoothing capacitor C0 connected via a parallel circuit of a capacitor C2 as
A diode D2 as a fourth rectifier between the two terminals of
A switching element Q1, which is a MOSFET connected through a parallel circuit of a capacitor C3 as a
A transformer T1 including a leakage transformer having a primary winding connected between a series circuit of Q2, a DC output terminal on the high potential side of the rectifier DB, and a connection point of the switching elements Q1 and Q2, and a secondary winding of the transformer T1. It comprises a load circuit 1 connected between both ends of the line, and a control circuit 2 for turning on / off the switching elements Q1 and Q2 alternately at a frequency sufficiently higher than the power supply frequency. The load circuit 1 includes a discharge lamp FL composed of a fluorescent lamp having power supply terminals of both filament electrodes connected between both ends of the secondary winding of the transformer T1, and a discharge lamp FL.
And a capacitor C1 for preheating and resonance connected between the non-power supply side terminals of both filament electrodes, and a resonance circuit is formed by the leakage inductance of the transformer T1 and the capacitor C1. In this circuit, in the circuit shown in FIG. 1 described above, the half cycle of the resonance voltage of the capacitor C3 near the peak value of the power supply voltage of the AC power supply AC (the peak portion of the pulsating voltage of the rectifier DB), and the ON state of the switching element Q1 The capacitance of the capacitor C3 is set so that the period is substantially equal. The basic operation of this circuit is the same as that of the above-described conventional example, and the crest factor of the current flowing through the load circuit 2 can be reduced without increasing the voltage across the smoothing capacitor C0. The following description focuses on the differences from the circuit described in the conventional example.

FIGS. 2A to 2C show high-frequency voltage waveforms of the voltage VQ2 applied to the switching element Q2 near the peak value of the AC power supply voltage.
(C) shows a capacitor C3 in one cycle of the AC power supply voltage.
3 shows a voltage waveform of the voltage Vc3 across the terminals. Here, when the capacitance of the capacitor C3 is small, the amplitude of the voltage Vc3 across the capacitor C3 increases as shown in FIG. 3A, so that the peak value VQ2peak of the voltage VQ2 applied to the switching element Q2 increases. The switching element Q2
It is necessary to use a device with a high breakdown voltage. Note that the half cycle of the resonance voltage of the capacitor C3 at this time is shorter than the ON period Ton of the switching element Q1 (that is, the OFF period of the switching element Q2) as shown in FIG.

On the other hand, when the capacitance of the capacitor C3 is large, the amplitude of the voltage Vc3 across the capacitor C3 decreases as shown in FIG. 3B, but the voltage across the capacitor C3 near the peak value of the AC power supply voltage. There is a region where Vc3 does not drop to 0V. This is because the half cycle of the resonance voltage of the capacitor C3 is longer than the ON period Ton of the switching element Q1, as shown in FIG. This is because Q1 is turned off. For this reason, when the switching element Q1 switches from the on state to the off state or when the switching element Q1 switches from the off state to the on state, the voltage VQ2 applied to the switching element Q2 becomes higher than the voltage Vdc across the smoothing capacitor C0. Loss increases.

Therefore, in the circuit of the present embodiment, the static period of the capacitor C3 is set so that the half period of the resonance voltage of the capacitor C3 near the peak value of the AC power supply voltage is substantially equal to the ON period Ton of the switching element Q1. Since the capacitance is set, the amplitude of the voltage Vc3 across the capacitor C3 is reduced as shown in FIG. 3C, as compared with the case where the capacitance of the capacitor C3 is small (see FIG. 3A). ,and,
As shown in FIG. 2C, the voltage VQ2 applied to the switching element Q2 when the switching element Q1 switches from the on state to the off state or when the switching element Q1 switches from the off state to the on state is equal to the voltage Vdc across the smoothing capacitor C3. It can be made substantially equal, and the peak value VQ2peak of the voltage VQ2 applied to the switching element Q2 can be reduced without increasing the switching loss. Therefore, a low withstand voltage element can be used for the switching elements Q1 and Q2, and the cost of the circuit can be reduced.

(Embodiment 2) FIG. 4 shows a circuit diagram of a power supply device of this embodiment. In this circuit, a variable capacitor C4 is used instead of the capacitor C3 having a fixed capacitance in the circuit of the first embodiment.
Similarly, the capacitor C near the peak value of the AC power supply voltage
By setting the capacitance of the capacitor C4 so that the half period of the resonance voltage of the switching element 4 and the on-period of the switching element Q1 are substantially equal, the voltage applied to the switching element can be reduced without increasing the switching loss. Therefore, a switching element having a low withstand voltage can be used. Here, the variable capacitance type capacitor C4 constitutes a variable capacitance means.

In the circuit of FIG. 4, the capacitance of the capacitor C4 can be changed to a desired value.
Even when the on-periods of the switching elements Q1 and Q2 change, as in the case of suppressing the output fluctuation of the load by changing the switching frequency and the on-duty of the switching elements Q1 and Q2, The voltage applied to the switching element Q2 is reduced without increasing the switching loss by changing the capacitance of the capacitor C4 such that the on-period of the switching element Q1 substantially matches the half cycle of the resonance voltage of the capacitor C4. However, an element having a low withstand voltage can be used by the switching elements Q1 and Q2.

Here, as shown in FIG. 5, in the circuit shown in FIG. 1, a parallel circuit of a capacitor C5 and a switching element Q3 as a capacitance varying means is connected via a capacitor C3 between both ends of a diode D2. The control circuit 2 turns on and off the switch element Q3 to select whether to connect the capacitor C5 in series with the capacitor C3 or to disconnect the capacitor C3.
Can be switched in two stages.

As shown in FIG. 6, in the circuit shown in FIG. 1, a series circuit of a capacitor C6 and a switching element Q4 serving as a capacitance varying means may be connected in parallel with the capacitor C3. By turning on and off the element Q4, the capacitor C3 is connected in parallel with the capacitor C3.
6 can be selected or not, and the combined value of the capacitances of the capacitors C3 and C6 can be switched in two stages.

(Embodiment 3) FIG. 7 is a circuit diagram of a power supply device according to this embodiment. In the circuit shown in FIG. 1 described above, a series circuit of the capacitor C2 and the diode D1 is connected between the connection point between the primary winding of the transformer T1 and the DC output terminal of the rectifier DB and one end of the smoothing capacitor C0. However, in the circuit of the present embodiment, in the circuit shown in FIG. 1, a capacitor C2 as a first capacitor is connected between the DC output terminals of the rectifier DB, and a connection point between the primary winding of the transformer T1 and the DC output terminal of the rectifier DB. , A cathode of the diode D1 is connected to one end of a smoothing capacitor C0, and a connection point of the diode D1 and the smoothing capacitor C0 and a series circuit of the switching elements Q1 and Q2. And a parallel circuit of a capacitor C3 as a second capacitor and a diode D2 as a fourth rectifier. There. In this circuit, the voltage between both ends of the capacitor C2 is the voltage between both ends Vdc of the smoothing capacitor C0 and the output voltage | Vs | of the rectifier DB.
Since the operation is the same as that of the circuit shown in FIG. 1 except that the waveform is clamped by, the description thereof is omitted. In this circuit as well, as in the circuit shown in FIG.
The crest factor of the current flowing through the load circuit 2 can be reduced without increasing the voltage across the zero.

Here, similarly to the first embodiment, the capacitor C3 is set so that the half period of the resonance voltage of the capacitor C3 near the peak value of the AC power supply voltage is substantially equal to the on-period Ton of the switching element Q1. Since the capacitance is set, the amplitude of the voltage Vc3 across the capacitor C3 is made smaller than when the capacitance of the capacitor C3 is small,
Further, when the switching element Q1 switches from the on state to the off state or when the switching element Q1 switches from the off state to the on state, the voltage VQ2 applied to the switching element Q2 can be made substantially equal to the voltage Vdc across the smoothing capacitor C3. The peak value VQ2pe of the voltage VQ2 applied to the switching element Q2 without increasing the switching loss
ak can be reduced. Therefore, low withstand voltage elements can be used for the switching elements Q1 and Q2,
Circuit cost can be reduced. It is needless to say that the configuration of the present embodiment may be applied to the power supply device of the second embodiment, and the same operation and effect as the circuit of the present embodiment can be obtained.

By the way, in each of the above embodiments, the first and second switching means are constituted by the switching elements Q1 and Q2 composed of MOSFETs.
The parasitic diode (not shown) of the SFET also serves as the first and second rectifiers, so that the number of circuit components can be reduced and the cost can be reduced. Note that the first and second switching means are not intended to be limited to MOSFETs. Instead, bipolar transistors are used as the first and second switching means, and the first and second rectifiers are antiparallel to the bipolar transistors. A diode may be connected.

In each of the above embodiments, the switching element Q2 is connected between the DC output terminals of the rectifier DB via the primary winding of the transformer T1, but the primary of the transformer T1 is connected between the DC output terminals of the rectifier DB. The switching element Q1 may be connected via a winding, and the same operation and effect as described above can be obtained. Further, in each embodiment, the load circuit 2 is constituted by the discharge lamp FL. However, the load is not limited to the discharge lamp FL, but may be a load other than the discharge lamp FL.

[0030]

As described above, the first aspect of the present invention provides a rectifier for rectifying a power supply voltage of an AC power supply, a smoothing capacitor for smoothing the rectified voltage of the rectifier, and a high frequency alternately connected in parallel with the smoothing capacitor. First and second turned on and off
Series circuit of the switching means, first and second rectification means connected in anti-parallel to the first and second switching means, respectively, and a connection point between the first and second switching means and one DC of the rectifier. One end is connected to the connection point between the transformer whose primary winding is connected to the output terminal, the load circuit connected to the secondary winding of the transformer, and one DC output terminal of the rectifier and the primary winding of the transformer. A parallel circuit of a first capacitor and a third rectifier connected together and the other end connected to one terminal of the smoothing capacitor, a parallel circuit of the first capacitor and the third rectifier and a smoothing capacitor And a parallel circuit of a second capacitor and a fourth rectifier connected between a connection point of the first and second switching means and a series circuit of the first and second switching means. The second conde The capacitance of the second capacitor is set such that a half cycle of the resonance voltage applied to the first and second switching means is substantially equal to an on-period of the first or second switching means. When one of the second switching elements, one of which is connected to the second capacitor, is turned on, the voltage across the smoothing capacitor and the voltage across the second capacitor are applied across the other switching element. The voltage of the sum of
The half period of the resonance voltage of the second capacitor is substantially equal to the ON period of the first or second switching element.
Since the capacitance of the second capacitor is set, the second cycle of the resonance voltage is smaller than that in the case where the half cycle of the resonance voltage is shorter than the ON period.
The amplitude of the resonance voltage of the capacitor can be reduced, and when one of the switching elements is turned off, the second
Since all the charges accumulated in the capacitor are discharged, the voltage across the second capacitor when one of the switching elements switches from on to off or from off to on becomes substantially zero, and the other switching element The voltage applied to the switching element can be made substantially equal to the voltage across the smoothing capacitor, and the peak value of the voltage applied to the switching element can be reduced without increasing the switching loss. Since the peak value of the applied voltage can be reduced, an element having a low withstand voltage can be used as the switching element, so that there is an effect that the cost can be reduced.

According to a second aspect of the present invention, there is provided a rectifier for rectifying a power supply voltage of an AC power supply, a smoothing capacitor for smoothing the rectified voltage of the rectifier, and a first capacitor connected in parallel with the smoothing capacitor and alternately turned on and off at a high frequency. A first and second rectifying means connected in anti-parallel to the first and second switching means, respectively;
A transformer having a primary winding connected between a connection point of the second switching means and one DC output terminal of the rectifier, a load circuit connected to a secondary winding of the transformer, and a DC output terminal of the rectifier. A first capacitor connected therebetween;
A third rectifier having one end connected to a connection point between the primary winding of the transformer and one DC output terminal of the rectifier and having the other end connected to one terminal of the smoothing capacitor;
And a parallel circuit of a second capacitor and a fourth rectifier connected between a connection point of the rectifier and the smoothing capacitor and a series circuit of the first and second switching means. The half period of the resonance voltage applied to the second capacitor near the peak value of the power supply voltage is substantially equal to the ON period of the first or second switching means.
The capacitance of the second capacitor is set, and one end of the first and second switching elements is connected to the second capacitor.
When one switching element connected to the capacitor is turned on, the sum of the voltage across the smoothing capacitor and the voltage across the second capacitor is applied across the other switching element. Since the capacitance of the second capacitor is set such that the half period of the resonance voltage of the second capacitor is substantially equal to the ON period of the first or second switching element, the half period of the resonance voltage is The amplitude of the resonance voltage of the second capacitor can be reduced as compared with the case where it is shorter than the ON period, and when one of the switching elements is turned off, all the electric charges accumulated in the second capacitor are discharged. Therefore, the voltage across the second capacitor when one of the switching elements switches from on to off or from off to on becomes substantially zero,
The voltage applied to the other switching element can be made substantially equal to the voltage across the smoothing capacitor, which has the effect of reducing the peak value of the voltage applied to the switching element without increasing the switching loss. Since the peak value of the voltage applied to the element can be reduced, an element having a low withstand voltage can be used as the switching element, so that the cost can be reduced.

According to a third aspect of the present invention, in the first or second aspect of the present invention, a capacitance changing means for changing the capacitance of the second capacitor is provided. Even if the on-period of the switching element changes as in the case of changing the switching frequency or on-duty of the switching element in accordance with the fluctuation, the capacitance variable means changes the power supply voltage of the AC power supply in accordance with the change of the on-period. Changing the capacitance of the second capacitor so that the half period of the resonance voltage applied to the second capacitor near the peak value is substantially equal to the ON period of the first or second switching means. As in the first or second aspect of the invention, there is an effect that the peak value of the voltage applied to the switching element can be reduced without increasing the switching loss. Can be reduced to a peak value of the voltage applied to the duck switching element, it is possible to use a low voltage elements by the switching element, there is an effect that it is possible to reduce the cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device according to a first embodiment.

2 (a) to 2 (c) are waveform diagrams for explaining the operation of the above.

FIGS. 3 (a) to 3 (c) are waveform diagrams for explaining the operation of the above.

FIG. 4 is a circuit diagram of another power supply device according to the first embodiment;

FIG. 5 is a circuit diagram of a power supply device according to a second embodiment.

FIG. 6 is a circuit diagram of another power supply device according to the first embodiment;

FIG. 7 is a circuit diagram of a power supply device according to a third embodiment.

8 (a) to 8 (h) are waveform diagrams of respective parts of a conventional power supply device.

FIGS. 9A to 9F are waveform diagrams of respective parts of the power supply device according to the first embodiment.

FIGS. 10A to 10C are waveform diagrams illustrating the operation of the above power supply device.

[Explanation of symbols]

 1 Load circuit C0 Smoothing capacitor C2, C3 Capacitor D1, D2 Diode DB Rectifier FL Discharge lamp Q1, Q2 Switching element T1 Transformer

Claims (3)

[Claims] A rectifier for rectifying a power supply voltage of an AC power supply;
A smoothing capacitor for smoothing the rectified voltage of the rectifier, a series circuit of first and second switching means connected in parallel with the smoothing capacitor and alternately turned on and off at a high frequency;
First and second rectifiers connected in anti-parallel to the first and second switching means, respectively, and a primary winding between a connection point of the first and second switching means and one of the DC output terminals of the rectifier. One end is connected to the connection point between the transformer connected to the wire, the load circuit connected to the secondary winding of the transformer, and the primary winding of the transformer and one of the DC output terminals of the rectifier, and the smoothing capacitor is connected. A first capacitor and a parallel circuit of the third rectifier, the other end of which is connected to one terminal, and a connection point between the parallel circuit of the first capacitor and the third rectifier and the smoothing capacitor. A second capacitor connected in series with the series circuit of the second switching means and a parallel circuit of the fourth rectifying means, which is applied to the second capacitor near a peak value of the power supply voltage of the AC power supply. Half period of resonance voltage As the on period of the first or second switching means are substantially equal, the power supply and wherein the capacitance of the second capacitor is set. 2. A rectifier for rectifying a power supply voltage of an AC power supply,
A smoothing capacitor for smoothing the rectified voltage of the rectifier, a series circuit of first and second switching means connected in parallel with the smoothing capacitor and alternately turned on and off at a high frequency;
First and second rectifiers connected in anti-parallel to the first and second switching means, respectively, and a primary winding between a connection point of the first and second switching means and one of the DC output terminals of the rectifier. A transformer connected to a wire, a load circuit connected to a secondary winding of the transformer, a first capacitor connected between the DC output terminals of the rectifier, a DC winding of the primary winding of the transformer and one of the rectifiers. A third rectifier having one end connected to a connection point with the terminal and the other end connected to one terminal of the smoothing capacitor; a connection point between the third rectifier and the smoothing capacitor; A second capacitor connected in series with the series circuit of the second switching means and a parallel circuit of the fourth rectifying means, which is applied to the second capacitor near a peak value of the power supply voltage of the AC power supply. The half cycle of the resonance voltage Or so that the ON period of the second switching means are substantially equal, the power supply and wherein the capacitance of the second capacitor is set. 3. The power supply device according to claim 1, further comprising capacitance changing means for changing the capacitance of said second capacitor.