JP2002159171A - Power source and discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a suppression of a surge voltage with a low loss. SOLUTION: A DC-DC converter 2 is a back booster converter of a transformer configuration. A route of bypassing a surge energy stored in a leakage inductance of a primary side of a transformer 21 is formed of a third closed circuit obtained by connecting a second diode 28 and a second capacitor 26 in series with both ends of the transformer 21. Thus, a surge voltage generated when a switching element 22 is turned off is clamped at the capacitor 26 via the diode 28, and a surge energy stored in the capacitor 26 when a secondary side current I2 flows is discharged to a smoothing capacitor 24 through a first diode 23 and a secondary winding L2. Thus, the surge voltage can be suppressed, and a loss by a snubber circuit can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for converting a DC power supply into a voltage to obtain a desired DC output, and a discharge lamp lighting device for lighting a discharge lamp using such a power supply.

[0002]

2. Description of the Related Art FIG. 9 shows an example of a conventional power supply device (hereinafter referred to as "conventional example 1"). The conventional example 1 includes a DC / DC conversion circuit 2 that converts the output of a DC power supply 1 such as a battery into a voltage, an output control circuit 61 that controls the output of the DC / DC conversion circuit 2, and a load circuit including a load 50. 5 is provided. The DC / DC conversion circuit 2 is composed of a conventionally known boost converter (boost converter), and boosts a voltage from a low-voltage power supply (DC power supply 1) such as a battery to a voltage required by a load 50 such as a discharge lamp. It is.

The output of the prior art 1 is mainly adjusted by a DC / DC conversion circuit 2, and the output current and output voltage are adjusted by a DC / DC converter.
Detected at the output end of the conversion circuit 2, the power command value generation circuit 60
Based on the power command value output from 1, the current command value calculation unit 602 calculates a control target value of the load current (lamp current) according to the detected value of the load voltage (lamp voltage), and performs feedback control. I have. The on / off control signal of the switching element 22 included in the DC / DC conversion circuit 2 is obtained by a triangular wave comparison method in which the output of the error amplifier 603 and the output of the triangular wave oscillator 604 are compared by a comparator 605, and the switching signal has a constant frequency. By changing the on-duty ratio, it becomes a PWM signal for performing output adjustment.

On the other hand, as shown in FIG. 10, a conventional example in which the load 51 is a discharge lamp and the DC / DC conversion circuit 2 is a flyback converter (hereinafter referred to as "conventional example 2").
There is also. The conventional example 2 includes a DC power supply 1, a DC / DC conversion circuit 2 including a flyback converter, and a load circuit 5. The load circuit 5 discharges a discharge lamp from the DC voltage obtained by the DC / DC conversion circuit 2. An inverter circuit 3 for supplying an alternating voltage to the discharge lamp 51 and a starting circuit 4 for applying a high voltage to start the discharge lamp 51 in an unlit state are provided. Here, since the discharge lamp 51 changes the lamp voltage from a low condition to a high condition as compared with the power supply voltage of the DC power supply 1, the DC / DC conversion circuit 2 needs to be flyback in order to cope with such a load. It is desirable to use a converter. That is, in the DC / DC conversion circuit 2 including the flyback converter, when the switching element 22 is turned on, the current I1 flows from the DC power supply 1 to the primary winding of the transformer 21, and energy is accumulated in the transformer 21. When the switching element 22 is turned off, the diode 23 is turned on by the back electromotive force due to the energy stored in the transformer 21, and the current I2 flows from the secondary winding to the capacitor 24, so that the output capacitor 24 is charged. By controlling the ON period and the OFF period of the switching element 22, the voltage of the output capacitor 24 can be changed from a lower condition to a higher condition than the power supply voltage of the DC power supply 1. Note that there is a buck-boost converter (a polarity inversion type chopper circuit) as a buck-boost converter that realizes a similar function.

Incidentally, the output control circuit 62 of the second conventional example may be PWM control of a fixed frequency as in the first conventional example.
The output control circuit 6 performs the following control to drive a load having a large output voltage fluctuation such as the discharge lamp 51 by using a battery or the like having a large voltage fluctuation as the DC power supply 1.

First, a power command value generation circuit 601
A power command value for determining the output power of the DC / DC conversion circuit 2 is generated, and the current command value calculation unit 602 outputs the power command value supplied from the power command value generation circuit 601 to the capacitor 24.
A current command value to be a control target of the output current of the DC / DC conversion circuit 2 is calculated from the voltage between both ends. Therefore, DC
The voltage between both ends of the capacitor 24 of the / DC conversion circuit 2 is detected by the output voltage detecting means and input to the current command value calculation unit 602 via the amplifier 607. The current command value calculated by the current command value calculation unit 602 becomes one input of the error amplifier 603. To the other input of the error amplifier 603, an output current detected by output current detecting means provided between the output of the DC / DC conversion circuit 2 and the input of the inverter circuit 3 is input via the amplifier 606. . The error amplifier 603 creates a primary peak current command from the current command value provided from the current command value calculation unit 602 and the detected value of the output current input via the amplifier 606,
The signal is input to the inverting input terminal of the comparator 610.

The transformer 21 of the DC / DC conversion circuit 2
The detected value of the secondary current I1 and the detected value of the secondary current I2 are input to the output control circuit 6. The detected value of the primary current I1 is input to the non-inverting input terminal of the comparator 610. When the detected value becomes larger than the primary peak current command, a reset signal is sent to the reset terminal of the oscillation circuit 608. The detected value of the secondary current I2 is input to the inverting input terminal of the comparator 609. The non-inverting input terminal of the comparator 609 is connected to the circuit ground. Therefore, when the detected value of the secondary current I2 becomes substantially zero, a set signal is sent from the comparator 609 to the set terminal of the oscillation circuit 608. The oscillation circuit 608 is configured to include a set / reset flip-flop, and controls on / off of the switching element 22 of the DC / DC conversion circuit 2 by the Q output.

That is, in the output control circuit 6 of the conventional example 2, the output of the error amplifier 603 serving as an output adjustment value is used as a peak command value of the current I1 flowing to the primary side of the transformer 21, and this command value and the primary side current The detected value of I1 is compared by the comparator 610, and when the detected value exceeds the command value, the Q output of the oscillation circuit 608 becomes L level, and the switching element 22 is turned off. After the switching element 22 is turned off, all the energy of the transformer 21 is discharged to the secondary side, and the comparator 609 detects that the secondary side current I2 becomes substantially zero, and sets the output of the oscillation circuit 608 to H level. The switching element 22 is turned on. That is, FIG.
1, an operation mode in which the switching element 22 for controlling the primary current I1 of the transformer 21 is turned on when the secondary current I2 of the transformer 21 becomes substantially zero is called a current boundary mode. By operating in the mode, the utilization rate of the transformer 21 can be increased. In the oscillation circuit 608, there is a case where the switching element 22 is turned off before the secondary current I2 becomes zero by providing a limit value to the maximum off period of the switching element 22 as shown in FIG. The lamp voltage is low as in a state where the electric lamp 51 is cold, and the secondary current I2
In order to prevent a rise in peak current due to a decrease in the switching frequency of the switching element 22 when the slope of the waveform is small, the above-mentioned limit value of the maximum off period is adjusted according to the state. In the output control circuit 6, the primary-side peak current value for turning off the switching element 22 is expressed by:
Output control is performed by adjusting by the same feedback control as in the first conventional example.

[0009]

FIG. 13 shows a DC / DC converter circuit 2 comprising a flyback converter as in the conventional example 2 or a chopper type converter using the transformer 21 as in the conventional example 1. As shown, the leakage inductances L1 _LK , L2
_{Due to the LK} , a surge voltage is generated in the switching element 22 during the switching operation of the switching element 22. Normally, an element having a withstand voltage capable of withstanding the surge voltage is used as the switching element 22, and a snubber circuit 29 as shown in FIG. 14 is provided at both ends of the transformer 21 and the switching element 22. However, there is a problem that the snubber circuit 29 causes a reduction in circuit efficiency because the surge voltage is lost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power supply device and a discharge lamp lighting device capable of suppressing a surge voltage with low loss.

[0011]

According to a first aspect of the present invention, there is provided a DC / DC conversion circuit for converting a power supply voltage of a DC power supply into a desired DC voltage, and a DC / DC conversion circuit. A DC / DC conversion circuit comprising: a transformer; a switching element for interrupting a current flowing from a DC power supply to a primary winding of the transformer; and a secondary winding of the transformer. A DC power supply, a primary winding and a switching element to form a closed primary side circuit, at least on both ends of the secondary winding and the secondary winding. A secondary side closed circuit including a series circuit including first and second diodes and a smoothing capacitor connected to each other is formed, and a direct circuit including at least a primary winding, a second diode, and a second capacitor is formed. Third closed circuit is formed including a circuit, the first transformer inductance component of the third closed circuit
A surge voltage generated when the switching element is turned off is clamped by a second diode and a second capacitor included in a third closed circuit, and the second capacitor is provided only as a secondary winding. Sends the surge energy stored in to the smoothing capacitor of the secondary side closed circuit,
Finally, by supplying the voltage to the load circuit, the surge voltage can be suppressed with low loss.

According to a second aspect of the present invention, in the first aspect of the present invention, a primary winding of a transformer is connected in series in the secondary side closed circuit. Has the effect of

According to a third aspect of the present invention, in the first aspect of the present invention, a DC power supply and a primary winding of a transformer are connected in parallel to the secondary side closed circuit. It has the same function as.

According to a fourth aspect of the present invention, there is provided the first or second or third aspect.
3. The method according to claim 1, wherein a smoothing capacitor is connected in series in the third closed circuit.
Alternatively, the same effect as that of the third invention is exerted.

[0015] The invention of claim 5 is the invention of claim 1 or 2 or 3.
The invention according to claim 1, wherein a DC power supply is connected in series in the third closed circuit, wherein the DC power supply is connected in series.
The same effect as that of the invention is achieved.

[0016] The invention of claim 6 is the invention of claim 1 or 2 or 3.
In the third aspect of the present invention, a DC power supply and a smoothing capacitor are connected in series in the third closed circuit, and the same effect as that of the first, second, or third aspect is obtained.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the switching element is turned on and off.
7. A control circuit for turning off the DC output of the DC / DC conversion circuit, the control circuit comprising:
The same effect as any of the inventions is achieved.

According to an eighth aspect of the present invention, in order to achieve the above object, the load according to the first to seventh aspects is a discharge lamp, and the surge voltage can be suppressed with low loss. A discharge lamp lighting device can be provided.

According to a ninth aspect of the present invention, in the eighth aspect of the present invention, the load circuit includes an inverter circuit which alternately supplies a DC output of a DC / DC conversion circuit to a discharge lamp. The same effect as the invention of Item 8 is exerted.

According to a tenth aspect, in the eighth or ninth aspect, the load circuit includes a starting circuit for applying a high voltage for starting to the discharge lamp. The same effect as that of the invention is achieved.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. However, in each of the following embodiments, the load circuit 5 having the same configuration as the load circuit 5 of the conventional example 2 in which the load 51 is a discharge lamp is provided, but the load circuit 5 and the load 51 are limited to those of the embodiment. Instead, the technical idea of the present invention can be applied to a case where a load circuit 5 having another configuration or a load circuit 5 having a load 51 other than a discharge lamp is provided.

(Embodiment 1) FIG. 1 shows a schematic circuit configuration diagram of a power supply device (discharge lamp lighting device) of the present embodiment. This embodiment includes a DC / DC conversion circuit 2 that converts a power supply voltage of a DC power supply 1 such as a battery into a desired DC voltage,
Load (not shown) by adjusting the DC output of DC conversion circuit 2
And a load circuit 5 for supplying the power to the power supply. However, since the basic configuration of this embodiment is the same as that of the conventional example 2, the same components are denoted by the same reference numerals and description thereof is omitted.

The DC / DC conversion circuit 2 includes a transformer 21
And a switching element 22 for interrupting the current I1 flowing from the DC power supply 1 to the primary winding L1 of the transformer 21, and a smoothing capacitor 24 connected to the secondary winding L2 of the transformer 21 via a rectifying element. This is a buck-boost converter with a transformer configuration. The primary winding L1 of the transformer 21 and the switching element 22 are connected in series to both ends of the DC power supply 1 to form a primary side closed circuit. Transformer 2
One secondary winding L2 has one end connected to the cathode of the first diode 23, and the other end connected to the switching element 22 and the primary winding L1 via the second diode 28. And one end of the smoothing capacitor 24 and one input end of the load circuit 5 are connected to the anode of the first diode 23, and the other end of the smoothing capacitor 24 is connected to the other input end of the load circuit 5 and the transformer 21. The other end of the primary winding L1 and the negative electrode of the DC power supply 1 are connected to form a secondary closed circuit. Further, the anode of the second diode 28, the other end of the primary winding L1 of the transformer 21, and the smoothing capacitor 2
2 between the connection point 4 and the second capacitor 2 for absorbing surge.
6 to form a third closed circuit composed of a series circuit of a primary winding L1 of the transformer 21, a second diode 28, and a second capacitor 26. The inductance component of the third closed circuit is only the primary winding L1 of the transformer 21.

The control circuit 6 has the same circuit configuration as the control circuit of the conventional example 1 or 2 and detects the output current and the output voltage of the DC / DC conversion circuit 2, and PWM control for varying the on-duty ratio of the switching element 22 so that the detected value becomes a desired value (see Conventional Example 1), or control for operating in the current boundary mode in a steady state (see Conventional Example 2) is performed. However, the configuration of the control circuit 6 is not limited to this, and another control may be performed.

The buck-boost converter having the transformer configuration does not usually include the second capacitor 26 and the second diode 28, and directly connects the primary winding L1 and the secondary winding L2 of the transformer 21. In general, the circuit operation is as follows.

First, when the switching element 22 is turned on, the current I1 is supplied from the DC power supply 1 to the primary winding L1 of the transformer 21.
Flows, and energy is stored in the transformer 21. When the switching element 22 is turned off, the energy stored in the transformer 21 is discharged to the smoothing capacitor 24 via the rectifying diode (first diode) 23 in the series circuit of the primary winding L1 and the secondary winding L2. . That is, by repeatedly turning on and off the switching element 22, the DC /
The DC conversion circuit 2 converts the power supply voltage of the DC power supply 1 into a DC voltage of a desired level and supplies the DC voltage to the load circuit 5.

Here, the surge voltage generated when the switching element 22 is turned off is determined by the fact that the surge energy stored in the leakage inductance on the primary side of the transformer 21 has no place to go and the energy stored in the transformer 21 This is because the secondary side current I2 does not suddenly increase due to leakage inductance on the secondary side when discharging to the secondary side.

Therefore, the present invention provides a path for bypassing the surge energy stored in the leakage inductance on the primary side of the transformer 21, stores the surge energy in the capacitor, and sends the energy stored in the capacitor to the smoothing capacitor. Finally, by supplying the voltage to the load circuit 5, it is possible to suppress the surge voltage with low loss.

In this embodiment, the path is formed by a third closed circuit in which the second diode 28 and the second capacitor 26 are connected in series at both ends of the transformer 21. The surge voltage generated when the switching element 22 is turned off is clamped to the second capacitor 26 through the second diode 28, and the secondary current I2
When the current flows, the surge energy stored in the second capacitor 26 is discharged to the smoothing capacitor 24 via the first diode 23 and the secondary winding L2. Thus, the surge voltage can be suppressed and the loss due to the snubber circuit can be avoided.

As shown in FIG. 2, the second diode 28 and the second capacitor 26 are exchanged, and the transformer 2
1 is connected to the second capacitor 2 by the primary winding L1 and the secondary winding L2.
6, the same operation and effect can be obtained even if the polarity of the secondary winding L2 is inverted. In this case, the polarity of the voltage (output voltage) across the smoothing capacitor 24 is opposite to the circuit configuration of FIG.

As shown in FIG. 3, by connecting the second capacitor 26 between the anodes of the first and second diodes 23 and 28, the smoothing capacitor 2 is formed in the third closed circuit.
4 and the second diode 28 and the second capacitor 26 are exchanged as shown in FIG. 4, and the primary winding L1 and the secondary winding L2 of the transformer 21 are connected to the second winding.
The same operation and effect can be obtained by connecting the secondary winding L2 via the capacitor 26 and inverting the polarity of the secondary winding L2.

(Embodiment 2) FIG. 5 is a schematic circuit configuration diagram of a power supply device (discharge lamp lighting device) of the present embodiment.

[0033] DC / DC conversion circuit 2 in the present embodiment
Is a boost converter having a transformer configuration, in which a primary winding L1 of a transformer 21 and a switching element 22 are connected in series to both ends of a DC power supply 1 to form a primary side closed circuit. In addition, one end of the secondary winding L2 of the transformer 21 is connected to the anode of the first diode 23, and the other end of the secondary winding L2 is connected to the negative electrode of the DC power supply 1 via the second capacitor 26, The cathode of the first diode 23 and the DC power supply 1
A secondary side closed circuit is formed by connecting the smoothing capacitor 24 between the negative electrode and the negative electrode. Further, the anode of the second diode 28 is connected to the connection point between the primary winding L1 and the switching element 22, and the cathode of the second diode 28 is connected to the connection point between the secondary winding L2 and the second capacitor 26. Then, the DC power supply 1, the primary winding L1 of the transformer 21 and the second
A third closed circuit composed of a series circuit of the diode 28 and the second capacitor 26 is formed. Note that the inductance component of the third closed circuit is the primary winding L1 of the transformer 21.
There is only as.

The control circuit 6 has the same circuit configuration as the control circuit of the first or second conventional example, detects the output current and the output voltage of the DC / DC conversion circuit 2, and PWM control for varying the on-duty ratio of the switching element 22 so that the detected value becomes a desired value (see Conventional Example 1), or control for operating in the current boundary mode in a steady state (see Conventional Example 2) is performed. However, the configuration of the control circuit 6 is not limited to this, and another control may be performed.

Incidentally, the boost converter having the transformer configuration usually does not include the second capacitor 26 and the second diode 28, and the primary winding L of the transformer 21 is not provided.
Generally, a configuration in which the primary winding L2 is directly connected to the secondary winding L2,
The circuit operation is as follows.

First, when the switching element 22 is turned on, the current I1 is supplied from the DC power supply 1 to the primary winding L1 of the transformer 21.
Flows, and energy is stored in the transformer 21. When the switching element 22 is turned off, the energy stored in the transformer 21 is converted into a DC power supply 1 and a rectifying diode (first diode) 2 in a series circuit of a primary winding L1 and a secondary winding L2.
3 to the smoothing capacitor 24. That is, by repeatedly turning on and off the switching element 22, the DC / DC conversion circuit 2 converts the power supply voltage of the DC power supply 1 into a DC voltage of a desired level and supplies the DC voltage to the load circuit 5.

In this embodiment, one end of the primary winding L1 and one end of the secondary winding L2 of the transformer 21 are connected to the second diode 28, and the secondary winding L2 and the DC power supply 1 are connected. The path for bypassing the surge voltage is formed by a third closed circuit in which the second capacitor 26 is connected to the negative electrode, and the surge voltage generated when the switching element 22 is turned off is formed by the second closed circuit. The surge energy stored in the second capacitor 26 when the secondary current I2 flows is clamped to the second capacitor 26 via the diode 28 and the surge energy stored in the second capacitor 26 is applied to the first diode 23 and the secondary winding L2.
To the smoothing capacitor 24 via the. This allows
The surge voltage can be suppressed, and the loss due to the snubber circuit can be avoided.

As shown in FIG. 6, the second diode 28 and the second capacitor 26 are exchanged, and the transformer 2
1 is connected to the second capacitor 2 by the primary winding L1 and the secondary winding L2.
6, the same operation and effect can be obtained even if the polarity of the secondary winding L2 and the polarity of the first diode 23 are inverted. In this case, the polarity of the voltage (output voltage) across the smoothing capacitor 24 is opposite to the circuit configuration of FIG.

Further, as shown in FIG. 7, by connecting the second capacitor 26 between the cathodes of the first and second diodes 23 and 28, the smoothing capacitor 2 is formed in the third closed circuit.
The same operation and effect can be obtained even if the second diode 4 and the second capacitor 28 are connected in series or the second diode 28 and the second capacitor 26 are exchanged as shown in FIG.

[0040]

According to the first aspect of the present invention, there is provided a DC / DC conversion circuit for converting a power supply voltage of a DC power supply into a desired DC voltage;
A load circuit that adjusts a DC output of the C / DC conversion circuit and supplies the load to a load; the DC / DC conversion circuit includes: a transformer; And a smoothing capacitor connected to the secondary winding of the transformer via a rectifying element. A primary-side closed circuit is formed by the DC power supply, the primary winding, and the switching element. A secondary-side closed circuit including a series circuit including first and second diodes and a smoothing capacitor connected to both ends of the secondary winding is formed, and at least the primary winding, the second diode, and the second A third closed circuit including a series circuit composed of capacitors is formed, and the inductance component of the third closed circuit is only the primary winding of the transformer, and the switching element is turned off. Third surge voltage generated when that
Clamped by the second diode and the second capacitor included in the closed circuit, and the surge energy stored in the second capacitor is sent to the smoothing capacitor of the secondary side closed circuit and finally supplied to the load circuit. By doing so, there is an effect that the surge voltage can be suppressed with low loss.

According to a second aspect of the present invention, in the first aspect of the present invention, a primary winding of a transformer is connected in series in the secondary side closed circuit. Has the effect of

According to a third aspect of the present invention, in the first aspect of the present invention, a DC power supply and a primary winding of a transformer are connected in parallel to the secondary side closed circuit. It has the same effect as.

The invention of claim 4 is the invention of claim 1 or 2 or 3
3. The method according to claim 1, wherein a smoothing capacitor is connected in series in the third closed circuit.
Or, the same effect as that of the third invention can be obtained.

[0044] The invention of claim 5 is the invention of claim 1 or 2 or 3.
The invention according to claim 1, wherein a DC power supply is connected in series in the third closed circuit, wherein the DC power supply is connected in series.
The same effect as that of the invention is achieved.

The invention of claim 6 is the invention of claim 1 or 2 or 3
In the third aspect, a DC power supply and a smoothing capacitor are connected in series in the third closed circuit, and the same effects as those of the first, second, or third aspect are obtained.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the switching element is turned on and off.
7. A control circuit for turning off the DC output of the DC / DC conversion circuit, the control circuit comprising:
The present invention has the same effect as any one of the inventions.

According to an eighth aspect of the present invention, the load described in any of the first to seventh aspects is a discharge lamp, and a discharge lamp lighting device capable of suppressing a surge voltage with low loss can be provided. effective.

According to a ninth aspect of the present invention, in the invention of the eighth aspect, the load circuit includes an inverter circuit that alternately supplies a DC output of a DC / DC conversion circuit to a discharge lamp. The same effects as in the invention of Item 8 are exerted.

According to a tenth aspect of the present invention, in the eighth or ninth aspect, the load circuit includes a starting circuit for applying a high voltage for starting to the discharge lamp. The same effect as that of the invention is achieved.

[Brief description of the drawings]

FIG. 1 is a schematic circuit configuration diagram showing a first embodiment.

FIG. 2 is a schematic circuit configuration diagram showing another configuration of the above.

FIG. 3 is a schematic circuit configuration diagram showing still another configuration of the above.

FIG. 4 is a schematic circuit configuration diagram showing still another configuration of the above.

FIG. 5 is a schematic circuit configuration diagram showing a second embodiment.

FIG. 6 is a schematic circuit configuration diagram showing another configuration of the above.

FIG. 7 is a schematic circuit configuration diagram showing still another configuration of the above.

FIG. 8 is a schematic circuit configuration diagram showing still another configuration of the above.

FIG. 9 is a schematic circuit diagram showing a first conventional example.

FIG. 10 is a schematic circuit configuration diagram showing a second conventional example.

FIG. 11 is an operation waveform diagram in the case of the above current boundary mode.

FIG. 12 is an operation waveform diagram in the case of the above current continuous mode.

FIG. 13 is a schematic configuration diagram of a transformer in the above.

FIG. 14 is a schematic circuit configuration diagram showing another configuration of the DC / DC conversion circuit in the above.

[Explanation of symbols]

 Reference Signs List 1 DC power supply 2 DC / DC conversion circuit 5 Load circuit 21 Transformer L1 Primary winding L2 Secondary winding 22 Switching element 23 First diode 24 Smoothing capacitor 26 Second capacitor 28 Second diode

Claims (10)

[Claims] A DC / DC conversion circuit for converting a power supply voltage of a DC power supply into a desired DC voltage; and a load circuit for adjusting a DC output of the DC / DC conversion circuit and supplying the adjusted DC output to a load.
The DC / DC conversion circuit includes a transformer, a switching element for interrupting a current flowing from a DC power supply to a primary winding of the transformer, and a smoothing capacitor connected to a secondary winding of the transformer via a rectifying element. A primary-side closed circuit is formed by the DC power supply, the primary winding, and the switching element, and includes at least a secondary winding, first and second diodes connected to both ends of the secondary winding, and a smoothing capacitor. A secondary closed circuit including a series circuit is formed, and a third closed circuit including a series circuit including at least a primary winding, a second diode, and a second capacitor is formed. Characterized in that the inductance component of the power supply device comprises only the primary winding of the transformer. 2. The power supply device according to claim 1, wherein a primary winding of a transformer is connected in series in the secondary side closed circuit. 3. The power supply device according to claim 1, wherein a DC power supply and a primary winding of a transformer are connected in parallel to the secondary side closed circuit. 4. The power supply device according to claim 1, wherein a smoothing capacitor is connected in series in the third closed circuit. 5. The power supply device according to claim 1, wherein a DC power supply is connected in series in the third closed circuit. 6. The power supply device according to claim 1, wherein a DC power supply and a smoothing capacitor are connected in series in the third closed circuit. 7. The power supply according to claim 1, further comprising a control circuit that controls on / off of said switching element to vary a DC output of a DC / DC conversion circuit. apparatus. 8. A discharge lamp lighting device, wherein the load according to claim 1 is a discharge lamp. 9. The discharge lamp lighting device according to claim 8, wherein the load circuit includes an inverter circuit which alternately supplies a DC output of a DC / DC conversion circuit to a discharge lamp. 10. The discharge lamp lighting device according to claim 8, wherein the load circuit includes a starting circuit for applying a high voltage for starting to the discharge lamp.