JP2744009B2 - Power converter - Google Patents

Description

The present invention relates to a power converter for driving a load in a soft-start manner, and is particularly suitable for a high-frequency lighting device for a discharge lamp.

FIG. 6 is a circuit diagram of a conventional power converter. This circuit has first and second switching circuits. The first switching circuit includes a boost chopper circuit 1 for converting commercial power AC into DC power. Boost chopper circuit 1, the output terminal of the connected full-wave rectifier DB through the power switch SW to the commercial power source AC, is connected a series circuit of the inductance element L ₁ and the transistor Q _1, the transistor Q ₁ collector-emitter capacitor through the diode D ₁ between
C ₁ is connected, and both ends of the capacitor C ₁ are output terminals of the step-up chopper circuit 1. The second switching circuit includes an inverter circuit 2 connected to an output terminal of the boost chopper circuit 1. The inverter circuit 2 converts an input DC voltage into a high-frequency voltage and outputs the converted high-frequency voltage. An output terminal of the inverter circuit 2 is connected to a discharge lamp 5. The drive power supply of the control circuit 3 for generating the drive signal of the boost chopper circuit 1 is obtained by dividing the pulsating voltage output from the full-wave rectifier DB by the resistors R ₇ and R ₁₇ and smoothing it by the capacitor C _7. ing.

Hereinafter, the operation of the circuit of FIG. 6 will be described. When the power switch SW is turned on, the output voltage of the full-wave rectifier DB is
A low DC voltage that has been divided by R ₇ and R ₁₇ and smoothed by the capacitor C ₇ is supplied as a driving power source for the control circuit 3. Then, the transistor Q ₁ is being switched by the control circuit 3. First, the transistor Q ₁ is at ON, energy is accumulated current flows in the inductance element L _1,
When the transistor Q ₁ is off, the stored energy via the diode D _1, is discharged to the capacitor C _1.
At this time, since the voltage plus the voltage across the inductance element L ₁ to the output voltage of the full-wave rectifier DB is applied to the capacitor C _1, a voltage obtained by boosting the output voltage of the full-wave rectifier DB is obtained in the capacitor C ₁ Can be The voltage obtained at the capacitor C ₁ is converted into a high-frequency voltage by the inverter circuit 2 and supplied to the discharge lamp 5.

FIG. 7 is a circuit diagram of another conventional example. For this example, one end of the commercial power source AC, between the negative output terminal of the full-wave rectifier DB, a diode D ₀ of the rectifying and resistive R ₇ of current limiting,
Connecting a capacitor C ₇ for smoothing in series, which are connected to the Zener diode ZD for voltage regulation in parallel across the capacitor C _7. Voltage obtained across the capacitor C ₇ has a drive power supply of the control circuit 3. Other configurations and operations are the same as those of the circuit of FIG.

[Problems to be Solved by the Invention] In each of the above-described conventional examples, the pulsating voltage output from the full-wave rectifier DB is compared with a voltage (several volts to 20 V) required as a power supply for driving the control circuit 3. When very high voltages, the power dissipated by the resistor R ₇ spans to several W, efficiency is a problem that very poor. Further, rated as the resistor R ₇ has a problem that it requires a large resistance element of tens W.

Further, in each of the above conventional examples, there is a serious problem that when the discharge lamp 5 is used as a load, the life of the lamp is adversely affected. Hereinafter, this will be described in detail.

In Figure 8 each of the above conventional example, the voltage across V _c1 of the capacitor C ₁ in immediately after turning on the power switch SW,
Is a time chart showing increase in the voltage across V _c7 of the capacitor C _7. Voltage across V _c1 of the capacitor C ₁ is the output voltage of the chopper circuit 1, the input voltage of the inverter circuit 2. Further, the voltage across V _c7 of the capacitor C ₇ is a driving power supply voltage of the control circuit 3 which supplies a drive signal to the transistor Q ₁ in the chopper circuit 1. This voltage V _c7
If There reach operating voltage e ₀ of the control circuit 3, the control circuit 3 operates, in which the drive signal is supplied to the base of the transistor Q _1.

After the power switch SW is turned on, the rectified output of the full-wave rectifier DB, capacitor C ₁ is charged through the inductor L ₁ and the diode D _1, the charging voltage V _c1 of the capacitor C ₁ is the commercial power source AC Reach peak voltage V _ACP (about 140V). At this time, the drive power supply voltage V _c7 of the control circuit 3
Since the driving voltage has already reached the operating voltage e ₀ , the driving signal is supplied to the transistor Q ₁ . Thus, the transistor Q ₁ is initiating the switching operation already. Therefore, the energy stored in the inductance element L ₁ is discharged to the capacitor C _1, voltage V across the capacitor C _1
c1 is the voltage V _DC higher than the peak voltage V _ACP of the commercial power supply AC
become. Time to end voltage V _c1 of the capacitor C ₁ reaches the voltage V _DC is very a short time, after power switch SW, instantaneously reaches the voltage V _DC. Therefore, immediately after the power is turned on, a voltage V _DC higher than the peak voltage V _ACP of the commercial power supply AC is instantaneously given to the inverter circuit 2,
When the discharge lamp 5 is started, a high voltage is instantaneously applied, which causes a cold cathode discharge in the discharge lamp, thereby shortening the life of the discharge lamp 5.

Therefore, as shown in FIG. 9, there has been proposed a circuit devised so that a high voltage is not applied when the discharge lamp is started. In this conventional example, a DC input terminal of a high-frequency inverter circuit ₂ having discharge lamps l ₁ and l ₂ as loads is connected to an AC power supply AC via a full-wave rectifier DB and a power switch SW. Output transformer T ₁ of the inverter circuit 2 is the discharge lamp l _1, l ₂ and 2 light series connection such as a fluorescent lamp in the output winding N _2, output winding N ₂
The two discharge lamps l ₁ and l ₂ are turned on by the high-frequency voltage induced in. Non-power side terminal of the discharge lamp l ₁ of filaments f ₁₁ is connected to the non-power supply side terminal of the filament f ₂₁ of the discharge lamp l ₂ via the contact Rys of primary winding and the relay Ry of the current transformer T ₂ I have. Further, between one of the terminals of both the discharge lamp l _1, l ₂ of the other filament f _12, f ₂₂ is connected to the secondary winding of the current transformer T _2. The relay Ry is controlled by the timer circuit 7. The timer circuit 7 is operated, the capacitor C ₈ and the resistor R ₄ constituting a time constant circuit, the level detector 6, the bias resistor R _5, are composed of transistors Q _0, the output voltage from the driving power source 4 as the power supply I do. The driving power supply 4 is composed of a diode D ₆ for rectifying a voltage induced in the tertiary winding N ₃ of the output transformer T ₁ , a capacitor C ₆ for smoothing the rectified voltage, and a current limiting resistor R _8. It is configured.

Next, the operation of this circuit will be described. And a power switch SW and turned on and connects the commercial power supply AC to the circuit, the inverter circuit 2 is operated, voltage is induced in the tertiary winding N ₃ of the output transformer T _1, the timer circuit 7 starts its operation. The timer circuit 7 uses a capacitor C ₈ and a resistor R ₄ as a time constant circuit. The output of the level detector 6 is set to “High” level for a certain period determined by the time constant. Is set to “Low” level and stopped. When the output of the level detector 6 is in the "High" level, the transistor Q ₀ is turned on. By turning on the transistor Q _0, a current flows through the exciting coil of the relay Ry, the relay contact Rys is turned on. Thus, the output winding N ₂ of the output transformer T ₁ of the inverter circuit 3, filaments f _11, 1 winding of the current transformer T _2, the relay contact Rys is, a closed circuit of the filament f ₂₁ is formed, also the current transformer T ₂ of the discharge lamp l ₁ and the secondary winding, l ₂ of the filament f _12, current also flows through f _22, both discharge lamp l _1, filaments f ₁₁ of l _2, f ₁₂ and f _21, f ₂₂ is preheated Will be done.
Since the output transformer T ₁ is made of a magnetic leakage type transformer, the output voltage of the output winding N ₂ during preheating are reduced, the discharge lamp
l ₁ and l ₂ are only preheated, and do not start lighting.

After a lapse of a certain period, the level detector 6 of the timer circuit 7
Sets its output to "Low" level. Thus, the transistor Q ₀ is turned off, to cut off the current to the exciting coil of the relay Ry. As a result, the relay contact Lys is turned off, and the high-frequency preheating current flowing in the closed circuit is cut off.

As a result, the preheating of the discharge lamps l ₁ and l ₂ is stopped, a high voltage appears in the output winding N ₂ of the output transformer T ₁ of the inverter circuit 2, and the discharge lamps l ₁ and l ₂ are turned on. Thus, in a period of time set by the timer circuit 7 sufficiently to the discharge lamp l _1, filaments f ₁₁ of l _2, f ₁₂ and f _21, f ₂₂ flowing preheating current, increasing the filament temperature, then Since the lamp is turned on by applying a high voltage, the lamp life of the discharge lamps l ₁ and l ₂ is much longer than that of a system in which the lamp is turned on by applying a high voltage without applying a sufficient preheating current.

However, in this conventional example, the relay Ry is required, and the contact Rys of the relay Ry turns on and off a high-frequency preheating current, and the applied voltage is also a high voltage. And a large contact capacity is required. Also, if a semiconductor switch element such as a transistor is used instead of the relay Ry,
A high breakdown voltage is required, which causes problems such as an increase in cost, a decrease in reliability, and a complicated circuit configuration.

The present invention has been made in view of such a point,
It is an object of the present invention to provide a power conversion device capable of obtaining a power supply of a control circuit for generating a drive signal by a method with a small power loss and preventing a high voltage from being applied to a load when the power is turned on. It is in.

[Means for Solving the Problems] In the present invention, in order to solve the above-described problems, as shown in FIG. 1, a direct current including a boost type first switching circuit (step-up chopper circuit 1). In a power converter including a power supply, a second switching circuit (inverter circuit 2) connected to an output terminal of the DC power supply, and a load (discharge lamp 5) connected to an output terminal of the second switching circuit, A control circuit 3 for generating a drive signal for the switching element (transistor Q ₁ ) is provided in the first switching circuit, and is smoothed by the switching operation of the second switching circuit to generate a substantially smoothed DC low voltage. it is characterized in that the power supply 4 obtained from use capacitor C ₆ and the driving power source of the control circuit 3.

[Operation] In the present invention, the driving power supply 4 of the control circuit 3 that generates the driving signal of the switching element in the first switching circuit is charged by the switching operation of the second switching circuit. it is so arranged to obtain from the smoothing capacitor C ₆ to produce substantially smoothed DC low voltage, using existing switching circuits, to obtain the power of the control circuit 3 with less efficient manner power loss Can be. According to the present invention, the switching operation of the second switching circuit must be started before starting.
Power is not supplied to the control circuit 3 of the first switching circuit of the boost type. Therefore, an excessive voltage is not applied to the load 5 from the second switching circuit immediately after the power is turned on.

Embodiment 1 FIG. 1 is a circuit diagram of a first embodiment of the present invention. Less than,
The circuit configuration will be described. An AC input terminal of the full-wave rectifier DB is connected to the commercial power supply AC via a power switch SW. The boost chopper circuit 1 is connected to a DC output terminal of the full-wave rectifier DB. The boost chopper circuit 1
The DC output ends of the full-wave rectifier DB configuration, connected a series circuit of the inductance element L ₁ and the transistor Q _1, between the collector and emitter of the transistor Q _1, which connects the capacitor C ₁ in parallel via a diode D ₁ It has become. Both ends of the capacitor C ₁ are output terminals of the boost chopper circuit 1. An inverter circuit 2 is connected to an output terminal of the boost chopper circuit 1.

The inverter circuit 2 includes a transistor Q _2, Q ₃ for switching connected in series, the transistors Q _2,
Input DC voltage is applied to the series circuit of the Q _3. Parallel with one transistor Q _2, the capacitor C ₃ for coupling
Discharge lamp 5, the inductance element L _2, the current feedback transformer CT
A series circuit of the primary winding n ₁ of is connected. Between the filament f _1, f ₂ of the power supply side terminal of the discharge lamp 5 is connected to the capacitor C ₄ is parallel resonant, between the non-power supply side terminal, the capacitor C ₅ for preheating current supply connected in parallel Have been. It has two secondary windings n _2, n ₃ of the current feedback transformer CT, the transistor Q ₂ one secondary winding n ₂ via a bias resistor R ₂
Of which is connected between the base and emitter, and the other secondary winding n ₃ is connected between the base and emitter of the transistor Q ₃ through a bias resistor R _3. Furthermore, between the input terminal of the inverter circuit 2 is connected a series circuit of a resistor R ₁ and capacitor C ₂ is the connection point of the resistors R ₁ and capacitor C ₂ via the DIAC Q _4, the base of the transistor Q ₃ It is connected. These resistors R ₁ , capacitor C ₂ and diac Q ₄
Constitutes a starting circuit of the inverter circuit 2. Note that diodes D ₂ and D ₃ are connected in anti-parallel to the transistors Q ₂ and Q ₃ , but these diodes D ₂ and D ₃ are not necessarily required.

Between the collector and the emitter of the transistor Q ₃ for switching, via the capacitor C ₉ for coupling the primary winding of the transformer T ₃ is connected. 2 of the transformer T ₃
The next winding via a resistor R ₈ of diode D ₆ and current limiting for rectification, capacitor C ₆ for smoothing is connected. The voltage obtained between both ends of the capacitor C ₆ becomes the driving power source 4 of the control circuit 3.

Hereinafter, the operation of the present embodiment will be described. When the power switch SW is turned on, the AC voltage of the commercial power source AC is rectified by the full-wave rectifier DB, via the inductance element L ₁ and the diode D _1, a DC voltage is obtained which is smoothed in the capacitor C _1. At this time, the transistor Q ₁ is a non-operating state. Voltage of the capacitor C ₁ is, when supplied to the inverter circuit 2, the capacitor C ₂ is charged through the resistor R _1. When the voltage of the capacitor C ₂ reaches the breakover voltage of the diac Q _4, the transistor Q ₃ charges the capacitor C ₂ is
Is discharged through the base-emitter region. This transistor Q ₃ is turned on. After that, the current feedback transformer CT
The transistors Q ₂ and Q ₃ are turned on and off alternately by the feedback current obtained from the secondary windings n ₂ and n ₃ .

At this time, between the collector and emitter of the transistor Q ₃ are voltage galvanically switching occurs. Transformer T ₃ This voltage through the capacitor C ₉ for coupling
Is applied to the primary winding. Capacitor for coupling
DC component is cut by the C _9, flows high-frequency AC component in the primary winding of the transformer T _3. Therefore, the transformer T ₃
, A high-frequency AC voltage is obtained in the secondary winding. This by rectifying and smoothing by the diode D ₆ resistor R ₈ and the capacitor C _6, it is possible to obtain a driving power supply of the control circuit 3. By appropriately setting the turn ratio of the primary winding and the secondary winding of the transformer T _3, without using a Zener diode for voltage regulation, a low DC voltage suitable for driving power source 4 of the control circuit 3 Obtainable. As the transformer T _3, because of the use of what little power loss, the power consumed in order to obtain the driving power source 4 of the control circuit 3 is very small, significant efficiency improvement over the prior art Is what is done.

When the control circuit 3 operates, the transistor Q ₁ is turned on and off in the step-up chopper circuit 1. Thus, the boost chopper circuit 1 operates, and the output voltage from the boost chopper circuit 1 causes the inverter circuit 2 to operate at a high input voltage. In the steady state, the inductance element L ₂
A high voltage of high frequency is applied to both ends of the discharge lamp 5 by the configured LC resonant circuit capacitor C ₄ and C _5, the discharge lamp 5
Lights up.

The above operation will be described with reference to the time chart of FIG.
In the figure, V _c1 voltage across the capacitor C _1, V _c6 capacitor
The voltage across C ₆ , Vla, is the voltage across discharge lamp 5. First, t ₁ after the power switch SW is turned on, a period until the inverter circuit 2 starts oscillation, no voltage is applied to the discharge lamp 5. When the power switch SW is turned ON, the rectified output of the full-wave rectifier DB, capacitor C ₁ is charged through the inductor L ₁ and the diode D _1, the voltage across V _c1 is the commercial power source AC peak power V _ACP To rise. Thus, the starting circuit of the inverter circuit 2 is operated, the transistor Q ₃ is turned on, thereafter, the feedback current from the current feedback transformer CT, the transistor Q _2, Q ₃
Are turned on and off alternately, and oscillation continues.

Next, t ₂ gradually increases the power supply voltage V _c6 of the control circuit 3, a period until it reaches the operating voltage e _0. During the period of this t _2, the voltage V _c1 of the capacitor C ₁ reaches the peak voltage V _ACP of the commercial power source AC, the inverter circuit 2 is oscillating. However, the peak voltage V of the commercial power supply AC
_{Since the ACP} has a lower voltage than the boosted voltage _VDC , the amplitude of the high-frequency voltage Vla applied to the discharge lamp 5 is small. At this time, the voltage V _c6 of the drive power supply 4 of the control circuit 3 which supplies a drive signal to the transistor to Q ₁ for switching in the boost chopper circuit 1 is low level, the transistor Q ₁ is not switched. By the inverter circuit 2 continues to oscillate, the voltage V _c6 of the drive power supply 4 of the control circuit 3 gradually rises and reaches the operating voltage e ₀ of the control circuit 3, the base of the transistor to Q ₁ boosting chopper circuit 2 drive signal is applied to the switching operation of the transistor Q ₁ is started.

In the period of t _3, the transistor of the step-up chopper circuit 1
Q ₁ starts switching operation and the voltage V _{c1 of the} capacitor C ₁
Is the voltage V _DC boosted from the peak voltage V _ACP of the commercial power supply AC
Reach Voltage V _DC at which voltage V _c1 of capacitor C ₁ is boosted
, The amplitude of the high-frequency voltage Vla applied to the discharge lamp 5 becomes very high, and the discharge lamp 5 is turned on. period t ₄ is the time period the discharge lamp 5 is lighted.

As described above, in the present embodiment, the inverter circuit 2 starts to oscillate, in the period t ₂ until the boost chopper circuit 1 starts operating, the voltage across the discharge lamp 5
Vla is a high-frequency voltage having a low amplitude, and the discharge lamp 5 is not turned on, but the filaments f ₁ and f ₂ of the discharge lamp 5 are provided with capacitors.
Since the resonance current of C ₅ is flowing, filament f _1, f ₂ continues to be preheated. Further, during a period of t ₃ to operate the booster chopper circuit 1, the voltage applied to the discharge lamp 5 becomes a high voltage, but the discharge lamp 5 is lit, at this time, the filament f _1, f ₂ of the discharge lamp 5 Since the pre-heating has already been sufficiently performed, the oxide film applied to the filaments f ₁ and f ₂ is less consumed at the time of starting, and the lamp life is improved.

The period t ₂ from the inverter circuit 2 starts to oscillate, until the boost chopper circuit 1 starts operation, which can be freely adjusted by charging time constant of the capacitor C _6, preheating time required Capacitor C ₆
Should be set.

Embodiment 2 FIG. 3 is a circuit diagram of a second embodiment of the present invention. In the present embodiment, the inductance element L ₂ in the inverter circuit 2 is provided with a secondary winding n _5. This secondary winding n ₅
The diode bridge DB for rectifying the resistor R ₈ of current limiting
Through 2, capacitors C ₆ and resistor R ₆ for smoothing is connected, one end of the capacitor C ₆ is connected to the negative output terminal of the full-wave rectifier DB. When the inverter circuit 2 oscillates, the secondary winding n ₅ of the inductance element L ₂ is induced AC voltage, the AC voltage is rectified by the diode bridge DB2, it is smoothed by the capacitor C _6. The voltage obtained at both ends of the capacitor C ₆ becomes the driving power source 4 of the control circuit 3. As alternating voltage obtained at the secondary winding n ₅ of the inductance element L ₂ is several V to several tens V, by setting the turn ratio of the primary winding n ₄ and the secondary winding n ₅ , the resistance R ₈ of current limiting can be a resistor element having a small capacity. Therefore,
A DC low-voltage power supply can be obtained efficiently. Other configurations and operations are the same as those in the embodiment of FIG.

Third Embodiment FIG. 4 is a circuit diagram of a third embodiment of the present invention. In this embodiment, a push-pull inverter circuit 2 is used. The positive electrode side of the capacitor C ₁ is connected to the primary winding N ₁ of the center tap of the output transformer T ₁ via an inductance element L _3. 1 across the primary winding N ₁ of the output transformer T ₁ is connected to the negative electrode side of the capacitor C ₁ via the collector-emitter of each transistor Q _2, Q _3. The 1 both ends of the primary winding N ₁ of the output transformer T _1, a capacitor for resonance
C ₀ is connected in parallel. Based respective transistor Q ₂ and the transistor Q ₃ are a resistor R ₂ and the resistor R ₃ each via,
Output is connected to the intermediate tap of the transformer T _1, are respectively connected to both ends of the feedback winding N ₀ of the output transformer T _1.
Discharge lamp 5 is connected to the secondary winding N ₂ of the output transformer T _1. Output transformer T ₁ is made of a magnetic leakage transformer, the leakage inductance has become a limiting element of the discharge lamp 5. A part of the secondary winding N ₂ is in the preheating winding of the filament of the discharge lamp 5.

When the input voltage is applied to the inverter circuit 2, via a respective inductance element L ₃ resistor R ₂ and the resistor R _3, current flows to the base of the transistor Q ₂ and the transistor Q _3, the transistor Q ₂ or Q ₃ Is turned on first. Now, if the transistor Q ₂ is and as a result, it becomes on state earlier than the transistor Q _3, the inductance element L ₃
Current flowing through the passes through the primary winding N ₁ of the center tap of the output transformer T _1, flows between the transistor Q ₂ collector-emitter. By that current flows through the primary winding N ₁ of the output transformer T _1, a forward bias the transistor Q _2, the orientation in the transistor Q ₃ to apply a reverse bias, the output transformer T ₁
Voltage is induced in the feedback winding N _0. Next, the capacitor C ₀
The feedback winding due to the resonance of the primary winding N ₁ of the output transformer T ₁ and
A voltage in the reverse direction is induced in N ₀ , and this feedback winding
Due to the voltage induced at N ₀ , transistor Q ₂ is reverse biased, transistor Q ₃ is forward biased, transistor Q ₂ is turned off, and transistor Q ₃ is turned on. Hereinafter, the same operation is repeated, and the output transformer T ₁ 2
High frequency voltage is induced in winding N _2, the high frequency voltage is applied to the discharge lamp 5.

In this embodiment, as in the embodiment shown in FIG. 1, between the collector and emitter of the transistor Q ₃ for switching,
Via the capacitor C ₉ for coupling the primary winding of the transformer T ₃ is connected. The secondary winding of the transformer T _3, via the diode D ₆ and resistor R ₈ of current limiting for rectification, capacitor C ₆ for smoothing is connected. The voltage obtained between both ends of the capacitor C ₆ becomes the driving power source 4 of the control circuit 3. On the transistor Q ₃ for switching at a high frequency, by turning off operation, for the operation of the driving power source 4 is obtained, which is similar to the embodiment shown in Figure 1.

Embodiment 4 FIG. 5 is a circuit diagram of a fourth embodiment of the present invention. In the present embodiment, the output transformer T ₁ in the inverter circuit 2 of the push-pull is provided with a tertiary winding N _3. A smoothing capacitor C ₆ and a resistor R ₆ are connected to the tertiary winding N ₃ via a current limiting resistor R ₈ and a rectifying diode bridge DB 2.
₆ is connected, one end of the capacitor C ₆ is connected to the negative output terminal of the full-wave rectifier DB. Inverter circuit 2
When but oscillates, the tertiary winding N ₃ of the output transformer T ₁ is induced AC voltage, this AC voltage the diode bridge DB2
Is rectified by, it is smoothed by the capacitor C _6. The voltage obtained at both ends of the capacitor C ₆ becomes the driving power source 4 of the control circuit 3. As alternating voltage obtained at the tertiary winding N ₃ of the output transformer T ₁ is made in several V to several tens V, by setting the turns ratio, the resistance R ₈ of current limiting in the resistance element of a small capacity Can be configured. The configuration and operation of the push-pull inverter circuit 2 are the same as in the embodiment of FIG.

In addition, it goes without saying that the present invention can be applied to a soft start drive of a load (for example, an incandescent lamp, a heating wire, an electric motor, or the like) to which stress is likely to be applied when the power is turned on, in addition to the discharge lamp 5.

[Effect of the Invention] In the power converter of the present invention, the power supply of the control circuit for generating the drive signal of the switching element in the first switching circuit of the boost type is changed by the switching operation of the second switching circuit. Since it is obtained from a smoothing capacitor that generates a substantially smoothed DC low voltage when charged, the existing switching circuit is used,
There is an effect that the power supply of the control circuit can be obtained in an efficient manner with less power loss, and there is an advantage that the circuit efficiency is increased and the size can be reduced. Also, power is not supplied to the booster-type first switching circuit control circuit until the switching operation of the second switching circuit starts, so that an excessive voltage is applied to the load from the second switching circuit immediately after the power is turned on. Can be prevented from being applied, the load stress can be reduced, and the life of the load can be improved.

When the load is a discharge lamp, cold cathode discharge can be prevented by preventing application of an overvoltage immediately after the power is turned on, so that the effect of improving the lamp life is particularly great.

[Brief description of the drawings]

1 is a circuit diagram of a first embodiment of the present invention, FIG. 2 is an operation waveform diagram of the above embodiment, FIG. 3 is a circuit diagram of a second embodiment of the present invention, and FIG. 4 is a third embodiment of the present invention. FIG. 5 is a circuit diagram of a fourth embodiment of the present invention, FIG. 6 is a circuit diagram of a conventional example, FIG. 7 is a circuit diagram of another conventional example, and FIG. FIG. 9 is a circuit diagram of still another conventional example. 1 is a step-up chopper circuit, 2 is an inverter circuit, 3 is a control circuit, 4 is a driving power supply, and 5 is a discharge lamp.

Claims (1)

(57) [Claims] 1. A DC power supply including a first switching circuit of a boost type, a second switching circuit connected to an output terminal of the DC power supply, and a load connected to an output terminal of the second switching circuit. In the power conversion device, a control circuit for generating a drive signal for a switching element is provided in a first switching circuit, and a smoothing that is charged by a switching operation of a second switching circuit to generate a substantially smoothed DC low voltage A power supply obtained from a capacitor for use as a drive power supply for the control circuit.