JP2000125567A - Power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cost by reducing the breakdown voltage of each element by suppressing the increase in a voltage across a smoothing capacitor when lightly loaded. SOLUTION: A smoothing capacitor C0 is connected between the DC output terminals of a rectifier DB via a diode D1, and a capacitor C3 is connected in parallel with the diode D1. An inverter circuit INV is provided with the series circuit of switching elements Q1 and Q2 which are connected between both terminals of the smoothing capacitor C0. A capacitor C1 is connected between the connection point of the rectifier DB and the diode D1 and that between the switching elements Q1 and Q2, via the series circuit of a choke coil L1 and a coupling capacitor C4. The series resonance circuit of the inductor L2 and the capacitor C2 is connected between both the terminals of the capacitor C1 via the diode D1 and a load Z is connected in parallel with the capacitor C2. When lightly loaded, a control circuit 2 controls the operating frequency of the inverter circuit INV to bring it close to an antiresonance frequency where a current flowing to the capacitor C1 can be minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a rectifying AC power supply,
The present invention relates to a power supply device that converts a DC voltage obtained by smoothing into a high-frequency voltage and supplies it to a load.

[0002]

2. Description of the Related Art As a power supply device of this type, as disclosed in, for example, Japanese Patent Application Laid-Open No. 10-14257, a high-frequency distortion of an input current is reduced by a simple circuit configuration, and a load current including a low-frequency ripple is generated. Some have prevented this from occurring. FIG. 28 shows a circuit diagram of this power supply device. A rectifier DB for rectifying the AC power supply Vs,
, A switching element Q1, Q2 composed of a field effect transistor connected between both ends of the smoothing capacitor C0, and both ends of the high-potential side switching element Q1. A series circuit including a load circuit 1, a choke coil L1, and a coupling capacitor C4 connected therebetween;
The impedance element Z1 connected between the connection point of the rectifier DB and the diode D1 (that is, the DC output terminal on the high potential side of the rectifier DB) and the connection point of the load circuit 1 and the choke coil L1 is connected in parallel to the diode D1. And a control circuit 2 for controlling ON / OFF of the switching elements Q1 and Q2. Although not shown, an input filter is generally provided between the AC power supply Vs and the rectifier DB.

In this power supply device, as shown in FIGS. 29A and 29B, three voltages of a voltage Vc3 across a capacitor C3, a voltage Vdc across a smoothing capacitor C0, and an input voltage Vin from a rectifier DB. A pulse-like input current Id flows from the rectifier DB at a high frequency by the relationship between the rectifier DB and the high-frequency operation of the inverter circuit INV including the switching elements Q1 and Q2.

[0004] The operation of this circuit will be briefly described below.

In the circuit shown in FIG. 28, in an operation mode using a smoothing capacitor C0 as a power supply, a so-called half-bridge inverter circuit is constituted by switching elements Q1 and Q2, a load circuit 1, a choke coil L1, and a coupling capacitor C4. . When the switching element Q2 is turned on, the discharge current from the smoothing capacitor C0 changes to the smoothing capacitor C0 → the load circuit 1 → the choke coil L1 → the coupling capacitor C4 → the switching element Q2 → the path of the smoothing capacitor C0 and the smoothing capacitor C0 → the capacitor C3 → Impedance element Z1 → choke coil L1 →
Coupling capacitor C4 → switching element Q2 →
Flowing through the path of the smoothing capacitor C0, the capacitor C3 is charged, and energy is stored in the choke coil L1. Here, when the sum of the charging voltage Vc3 of the capacitor C3 and the input voltage Vin becomes substantially equal to the voltage Vdc across the smoothing capacitor C0, the resonance current stops flowing through the latter path, and the AC power supply Vs → rectifier DB → Impedance element Z1 → choke coil L1 → coupling capacitor C4 → switching element Q2 → rectifier DB
→ Resonant current flows in the path of AC power supply Vs, and input current Id
Is drawn in and attempts to continue the inverter operation.

Then, at the moment when the switching element Q2 is turned off and the switching element Q1 is turned on, the choke coil L1
The current flows through the path of the choke coil L1, the coupling capacitor C4, the switching element Q1, the load circuit 1, the choke coil L1, and the AC power supply Vs → the rectifier DB →
A current flows through the path of the impedance element Z1, the choke coil L1, the coupling capacitor C4, the switching element Q1, the smoothing capacitor C0, the rectifier DB, and the AC power supply Vs, and the smoothing capacitor C0 is charged.

After that, when all the energy stored in the choke coil L1 is released, the resonance operation of the resonance circuit is reversed, and the coupling capacitor C4 → the choke coil L1 → Load circuit 1 → switching element Q1 →
A resonance current flows through the path of the coupling capacitor C4 and the path of the coupling capacitor C4 → the choke coil L1 → the impedance element Z1 → the capacitor C3 → the switching element Q1 → the path of the coupling capacitor C4, and the capacitor C3 is charged by the latter path. The discharged charge is discharged. Here, when all the charges charged in the capacitor C3 are discharged, the resonance current flows through the diode D1 instead of the capacitor C3.

As described above, the input voltage V from the rectifier DB
in and the sum of the voltage Vc3 across the capacitor C3 (Vin
+ Vc3) becomes substantially equal to the voltage Vdc across the smoothing capacitor C0, the inverter operation using the smoothing capacitor C0 as a power supply stops, and the input current Id is drawn in to continue the inverter operation. The input current I from the AC power supply Vs over the entire period of the cycle
d can be drawn in, and high-frequency distortion included in the input current Id can be reduced and the power factor can be improved.

Further, by setting the impedance value of the impedance element Z1 to an appropriate value,
As shown in (a), the voltage Vz1 across the impedance element Z1 is proportional to the input voltage Vin of the pulsating current, and the ground level is reduced by the voltage Vc4 across the coupling capacitor C4 due to the DC cut operation of the coupling capacitor C4. A shifted voltage waveform results. Since the voltage Vc3 across the capacitor C3 is the difference between the voltage Vdc across the smoothing capacitor C0 and the input voltage Vin from the rectifier DB, FIG.
As shown in FIG. 0 (b), the voltage is a voltage obtained by subtracting the pulsating input voltage Vin from the voltage Vdc across the smoothing capacitor C0, which is substantially constant. The voltage V1 across the load circuit 1
Is the sum of the voltage Vc3 across the capacitor C3 and the input voltage Vin from the rectifier DB, and its voltage waveform is shown in FIG.
As shown in 0 (c), the voltage waveform has a small low-frequency ripple, and the load current flowing through the load circuit 1 can also be a current with a small low-frequency ripple.

FIG. 31 shows a specific circuit diagram of the power supply device described above. In this circuit, the load circuit 1 is constituted by a discharge lamp FL made of, for example, a fluorescent lamp, and a filament preheating and resonance capacitor C2 connected between the non-power-supply-side terminals of both filament electrodes of the discharge lamp FL. The impedance element Z1 is composed of a capacitor C1. In this circuit,
Since low-frequency ripple of the load current flowing through the load circuit 1 can be reduced, radiation noise, flickering of the discharge lamp, and the like can be suppressed.

[0011]

In the power supply device having the above-described structure, when the load circuit 1 is composed of the discharge lamp FL, the discharge lamp FL is used as in the case of the dimming lighting of the discharge lamp FL and the start of preheating.
That is, when the load circuit 1 has a large impedance (the current flowing through the discharge lamp FL is small) and the load is light, the resonance current flowing through the resonance circuit tends to increase, and the current Ic1 flowing through the capacitor C1 by charging the capacitor C3. Also increase. For this reason, the time required for charging the capacitor C3 is shortened, and the time required for drawing the input current Id is longer than at the time of rated lighting. Also, when the charging current of the capacitor C3 is large, the input current Id is drawn so as to continue the inverter operation when the path of the resonance current is switched after the charging of the capacitor C3 is completed. Will be drawn. However, at the time of light load, the consumed energy is smaller than at the time of the rated lighting, so that the energy is excessively drawn in. As a result, the surplus energy is reduced by the smoothing capacitor C.
As a result, the voltage Vdc across the smoothing capacitor C0 increases significantly. Therefore, the stress applied to each element at light load increases, and the smoothing capacitor C
0 and switching elements Q1 and Q2
It is necessary to design the value to be excessively large with respect to the withstand voltage required at the time of rated lighting, and there is a problem that the cost is increased.

If the inverter circuit INV is operated at a frequency much higher than the resonance frequency at a light load, the charging current of the capacitor C3 becomes small, so that the input current I
d is hardly pulled in, and the voltage Vdc across the smoothing capacitor C0 hardly rises. However, since the resonance of the resonance circuit is in a very weak frequency range, the output of the inverter circuit INV has a very small value almost close to zero. Become. Therefore, in the circuit of FIG. 31 described above, in order to obtain an arbitrary output at a light load, it was necessary to design in consideration of an increase in stress applied to each element due to the increase of the voltage Vdc across the smoothing capacitor C0. .

The circuit shown in FIG. 31 is a discharge lamp FL.
And a capacitor preheating system for preheating the filament electrode by a capacitor C2 connected between the non-power-supply-side terminals of both filament electrodes of the discharge lamp FL.
The control circuit 2 controls the operating frequency of the inverter circuit INV and changes the ratio of the impedance between the discharge lamp FL and the capacitor C2, thereby changing the filament current flowing through both filament electrodes of the discharge lamp FL.
At the time of dimming lighting, the filament current is increased as compared with the rated lighting.

In recent years, there has been a tendency to reduce the diameter of a discharge lamp for the purpose of downsizing lighting equipment, increasing the efficiency of the discharge lamp, and saving resources. For example, a fluorescent lamp conventionally provided with a rated power consumption of 20 W or more has a tube diameter of 36.5.
In contrast to the fluorescent lamps having a diameter of 16 mm, there is a fluorescent lamp having a tube diameter of 16 mm provided under a name such as TL'5 (a product of Philips) or T5. In such a small-diameter discharge lamp, the filament diameter of the filament coil tends to be further reduced so that a sufficient length of the filament coil can be secured inside the discharge lamp. Therefore, in order to extend the life of the filament coil (that is, the lamp life), an upper limit value is provided for the filament current when the discharge lamp is turned on, and the upper limit value is lower than the lower limit value of the filament current during the pre-heating. Stipulated. Therefore, in the above-described circuit of the capacitor preheating method, when the filament current increases during dimming lighting, the filament current may exceed the upper limit value, and the lamp life may be shortened.

Further, in the case of a small-diameter discharge lamp, the difference between the lower limit value of the no-load secondary voltage for preventing the discharge lamp FL from lighting during preheating and the voltage across the discharge lamp FL during dimming lighting. And the discharge lamp FL has a relatively high impedance, so that there is not much difference in the resonance characteristics between no load (during preheating) and dimming lighting. As a result, in the capacitor preheating circuit, The difference between the operating frequency of the inverter circuit during preheating and the operating frequency of the inverter circuit during dimming lighting is reduced. Thus,
It is difficult to make a difference in the filament current between the pre-heating and the dimming operation, so that the filament current can be sufficiently secured at the pre-heating and the filament current is lower than the upper limit value during the dimming operation. Is difficult to set.

By the way, in order to increase the difference in operating frequency of the inverter circuit between the preheating of the capacitor and the operation of the dimming in the circuit of the capacitor preheating method, it is sufficient to increase the DC voltage of the DC voltage source of the resonance circuit. However, when the DC voltage is increased, the breakdown voltage of each element is increased, resulting in an increase in cost. Further, in order to increase the difference in operating frequency of the inverter circuit between the time of preceding preheating and the time of dimming lighting, a device using a filament inverter as disclosed in JP-A-10-134984 is also disclosed. In order to preheat the filament electrode of the discharge lamp, it is necessary to add an element such as a transformer, and there has been a problem that an increase in the number of elements leads to an increase in cost.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to suppress a rise in voltage across a smoothing capacitor under a light load and reduce the withstand voltage of each element. Another object of the present invention is to provide a power supply device at low cost.

[0018]

In order to achieve the above object, according to the first aspect of the present invention, a rectifier for rectifying an AC power and a smoothing device connected between a DC output terminal of the rectifier via a first diode. A capacitor, an inverter circuit that converts a voltage between both ends of the smoothing capacitor into a high-frequency voltage and supplies the load to a load, a control circuit that controls an operating frequency of the inverter circuit, and a rectifier through a series circuit of the coupling capacitor and the first inductor Feedback means for feeding back a part of the output of the inverter circuit to a connection point between one of the DC output terminals and the first diode; and a first capacitor connected in parallel to the first diode. , A second capacitor connected between a series circuit of the coupling capacitor and the first inductor and one DC output terminal of the rectifier. A series resonant circuit including at least an inductor and a capacitor is connected between both ends of the second capacitor via the first diode, and a load is connected in parallel with an impedance element included in the series resonant circuit; At this time, the control circuit controls the operation frequency of the inverter circuit to approach an anti-resonance frequency at which the current value of the current flowing to the load or the feedback means is minimized. When the voltage becomes almost equal to the difference between the voltage across the smoothing capacitor and the input voltage from the rectifier, the input current is drawn.
Since the input current pull-in period is determined by the current flowing through the feedback means relating to the charging of the first capacitor, the control circuit reduces the current flowing through the feedback means by bringing the operating frequency of the inverter circuit closer to the anti-resonance frequency at light load. It is possible to reduce the length of time required for charging the first capacitor, shorten the period for drawing in the input current, suppress the voltage increase across the smoothing capacitor at light load, and reduce the stress applied to each element. Can be reduced.

According to a second aspect of the present invention, a rectifier for rectifying an AC power supply, a smoothing capacitor connected between the DC output terminals of the rectifier via a first diode, and a voltage across the smoothing capacitor converted to a high-frequency voltage. Circuit for controlling the operating frequency of the inverter circuit, and a connection point between one DC output terminal of the rectifier and the first diode via a series circuit of the coupling capacitor and the first inductor. And a first capacitor connected in parallel to a first diode, the feedback unit comprising: a series circuit of a coupling capacitor and a first inductor; A second capacitor connected between one of the DC output terminals of the rectifier, the coupling capacitor and the first capacitor; A series resonance circuit including at least an inductor and a capacitor is connected between a connection point between the series circuit of the inductor and the second capacitor and the other DC output terminal of the rectifier, and an impedance element included in the series resonance circuit The control circuit controls the inverter so that the operating frequency of the inverter circuit approaches an anti-resonance frequency that minimizes the value of the current flowing through the load and the feedback means when the load is light. When the voltage across the first capacitor becomes substantially equal to the difference between the voltage across the smoothing capacitor and the input voltage from the rectifier, the input current is drawn.
Since the input current pull-in period is determined by the current flowing through the feedback means relating to the charging of the first capacitor, the control circuit reduces the current flowing through the feedback means by bringing the operating frequency of the inverter circuit closer to the anti-resonance frequency at light load. It is possible to reduce the length of time required for charging the first capacitor, shorten the period for drawing in the input current, suppress the voltage increase across the smoothing capacitor at light load, and reduce the stress applied to each element. Can be reduced.

According to a third aspect of the present invention, in the first or second aspect of the present invention, there are two resonance frequencies in the frequency characteristics of the current flowing through the load and the feedback means, and the control circuit reduces the operating frequency of the inverter circuit to a low frequency. The control is performed between the resonance frequency on the side and the anti-resonance frequency, and the same operation as in claim 1 or 2 is achieved.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the control circuit controls the operating frequency of the inverter circuit so that a current flowing through the feedback means at a light load is smaller than at a rated load. By reducing the current flowing to the feedback means at light load,
Similarly to the first and second aspects of the present invention, the time required for charging the first capacitor can be lengthened to shorten the input current pull-in period, so that the voltage across the smoothing capacitor is boosted at light load. Can be suppressed.

According to a fifth aspect of the present invention, in the first or second aspect of the invention, there are two resonance frequencies in the frequency characteristics of the current flowing through the load and the feedback means, and the load has a discharge lamp having a filament electrode at both ends. A capacitor for preheating is connected between the non-power-supply-side terminals of both filament electrodes so that a current equal to or less than the upper limit of the filament current when the discharge lamp is lit is connected.
While the filament current is within the current range necessary for preheating, the voltage across the discharge lamp is equal to or less than a predetermined upper limit, and the current flowing through the feedback means has a current value corresponding to the power consumption during preheating. The frequency difference between the high-frequency side resonance frequency and the anti-resonance frequency is set. By setting the high-frequency side resonance frequency and the anti-resonance frequency, the preheating current during the preheating can be easily set even in the capacitor preheating type circuit. Therefore, there is no need to provide a filament inverter for preheating the filament or to add an element such as a transformer for preheating, so that the cost of the preheating circuit can be reduced.

According to a sixth aspect of the present invention, in the invention of the fifth aspect, when the filament current during the preheating is smaller than a current range necessary for the preheating, the difference between the resonance frequency on the high frequency side and the antiresonance frequency is reduced. It is characterized in that it is set to be small, the minimum value of the current can be increased by reducing the frequency difference between the resonance frequency on the high frequency side and the antiresonance frequency, and the required filament current is increased by increasing the filament current. It can be within the current range.

According to a seventh aspect of the present invention, in the fifth aspect of the present invention, the filament current at the time of preheating is larger than the current range required for preheating, or the voltage across the discharge lamp during the preheating is a predetermined upper limit value. If higher, the difference between the resonance frequency on the high frequency side and the antiresonance frequency is set to be large, and the difference between the resonance frequency on the high frequency side and the antiresonance frequency is increased. As a result, the minimum value of the current can be reduced, and the filament current can be reduced to fall within a required current range.

According to an eighth aspect of the present invention, in the first or second aspect of the invention, a second diode is connected between the smoothing capacitor and the other DC output terminal of the rectifier, and the coupling capacitor and the first inductor are connected. Series circuit and second
A third capacitor is connected between a connection point of the rectifier and the other DC output terminal of the rectifier, and a fourth capacitor is connected in parallel with the second diode. By providing a current path passing through the fourth capacitor and the second diode, the input current can be drawn over substantially the entire period of one cycle of the input voltage, so that the peak value of the input current can be reduced.

According to a ninth aspect of the present invention, in the first or second aspect of the invention, the load comprises a discharge lamp having a filament electrode at both ends, and includes a coupling capacitor and a first capacitor.
The potential of the connection point between the series circuit of the inductor and the second capacitor is compared with a predetermined threshold voltage, and when the discharge lamp is not loaded or abnormal, the potential of the connection point is higher than the threshold voltage. The detection circuit outputs a detection signal to the control circuit, and the control circuit suppresses the voltage rise across the smoothing capacitor when the detection signal is input from the comparison detection circuit. The inverter circuit is operated at a frequency that can be used.When the comparison and detection circuit detects that the discharge lamp is unloaded or abnormal, the control circuit controls the operation frequency of the inverter circuit and the voltage across the smoothing capacitor. Is suppressed, so that stress applied to each element can be reduced.

According to a tenth aspect of the present invention, in the first or second aspect, the load comprises a discharge lamp having a filament electrode at both ends, and when the discharge lamp is removed, the current loop is eliminated in the series resonance circuit. In this case, the second inductor is constituted by a primary winding of a transformer, and
A current-to-voltage converter for detecting a current flowing in the next winding and generating a voltage corresponding to the current is provided. A comparison detection circuit is provided for outputting a detection signal to the control circuit when the output voltage of the current-to-voltage conversion means becomes lower than the threshold voltage during no load. The inverter circuit operates at a frequency at which the resonance of the resonance circuit becomes weaker with the lamp removed, and when the comparison detection circuit detects that the discharge lamp is not loaded, the control circuit operates the inverter circuit at the operating frequency. Is controlled so that the resonance of the resonance circuit is weakened, so that the voltage across the smoothing capacitor is prevented from rising, and the stress applied to each element can be reduced.

According to an eleventh aspect of the present invention, in the first or second aspect, the load comprises a discharge lamp having a filament electrode at both ends, and a current loop is formed in the series resonance circuit even when the discharge lamp is removed. When the discharge lamp is removed, the control circuit operates the inverter circuit at a frequency substantially equal to the anti-resonance frequency such that the current value of the current flowing through the feedback means when the discharge lamp is removed is minimized. The control circuit operates the inverter circuit at a frequency substantially equal to the anti-resonance frequency when there is no load, so the voltage across the smoothing capacitor is suppressed from increasing and the stress on each element is reduced. can do.

According to a twelfth aspect of the present invention, in the first or second aspect, the load comprises a discharge lamp having a filament electrode at both ends, and compares the level of the voltage between both ends of the smoothing capacitor with a predetermined threshold voltage. And a comparison detection circuit for detecting that the voltage between both ends becomes higher than the threshold voltage when the discharge lamp is unloaded or abnormal, and outputting a detection signal to a control circuit. When the detection signal is input from the inverter, the inverter circuit operates at a frequency that can suppress the voltage increase across the smoothing capacitor, and the comparison detection circuit detects when the discharge lamp is unloaded or abnormal. Then, the control circuit controls the operating frequency of the inverter circuit to suppress the voltage across the smoothing capacitor from increasing, so that the stress applied to each element can be reduced.

[0030]

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

(Embodiment 1) FIG. 1 shows a circuit diagram of a power supply device of the present embodiment. This circuit includes a rectifier DB for rectifying an AC power supply Vs, a smoothing capacitor C0 connected between a DC output terminal of the rectifier DB via a diode D1 as a first diode, and a voltage across the smoothing capacitor C0 as a high-frequency voltage. And an inverter circuit INV that converts and supplies the converted load to a load Z described later. The inverter circuit INV has a series circuit of switching elements Q1 and Q2 composed of MOS field-effect transistors connected between both ends of the smoothing capacitor C0. The switching elements Q1 and Q2 are controlled by a control signal a input from the control circuit 2. , B alternately turned on and off. A connection point between the DC output terminal on the high potential side of the rectifier DB and the diode D1, and the switching element Q1,
Between the connection point of Q2 and the coupling capacitor C4
A capacitor C1 as a second capacitor is connected through a series circuit of a choke coil L1 as a first inductor. A series resonance circuit of an inductor L2 and a capacitor C2 is connected between both ends of the capacitor C1 via a diode D1, and a load Z is connected in parallel with a capacitor C2 as an impedance element included in the series resonance circuit. Further, a capacitor C3 as a first capacitor is connected in parallel with the diode D1.
Here, the DC output terminal on the high potential side of the rectifier DB and the diode D
Feedback means for feeding back a part of the output of the inverter circuit INV to the connection point 1 is configured.

FIG. 2A shows the frequency characteristics of the current Iz flowing through the load Z, and FIG. 2B shows the frequency characteristics of the current Ic1 flowing through the capacitor C1. FIG. 2 (a)
In (b), the frequency characteristic at the time of rating is shown by a solid line, and the frequency characteristic at the time of light load is shown by an alternate long and short dash line. In this circuit, the choke coil L1 and the capacitor C1,
C3 resonance circuit, inductor L2 and capacitor C
There are two resonance frequencies f01 and f02 (f01 <f02) due to the two resonance circuits with the two resonance circuits. The frequency characteristic of the current Ic1 related to the charging of the capacitor C3 is such that the current Ic1 is between the two resonance frequencies f01 and f02.
Has a frequency characteristic in which an anti-resonance frequency f03 at which the minimum value exists is present (f01 <f03 <f02). Here, the anti-resonance frequency f03 is represented by Expression (1), where L2 is the inductance of the inductor L2 and C2 is the capacitance of the capacitor C2.

F03 = 1 / {2π (L2 · C2) ^1/2 } (1) Here, the control circuit 2 controls the operating frequency f of the inverter circuit INV, and operates at the rated lighting time. f
Is controlled to a frequency f1 higher than the resonance frequency f01, and at a light load, the operating frequency f is controlled to a frequency f2 higher than the frequency f1 and lower than the anti-resonance frequency f03 (f01 <f1 <f2 <f03). .

The operation of the present circuit will be described below with reference to FIGS. The operation at the time of rated lighting is substantially the same as that of the conventional circuit. Here, FIGS. 3 and 4 show an example of a circuit in which the load Z is, for example, a discharge lamp FL made of a fluorescent lamp in the circuit of FIG. Will be described. 3 and 4, the control circuit 2 is omitted, and the arrows in FIGS. 3 and 4 indicate paths through which current flows.

As shown in FIG. 3A, the capacitor C3
When both of the switching elements Q1 and Q2 are turned off in a state where the electric charge charged to the capacitor becomes zero, the coupling capacitor C4 is used as a power supply, and the coupling capacitor C4 → the choke coil L1 → the capacitor C1 → the diode D1 →
Smoothing capacitor C0 → parasitic diode (not shown) of switching element Q2 → path of coupling capacitor C4, coupling capacitor C4 → choke coil L
1 → discharge lamp FL, capacitor C2 → inductor L2 → smoothing capacitor C0 → parasitic diode of switching element Q2 → current path through coupling capacitor C4, and smoothing capacitor C0 is charged.

Thereafter, when the switching element Q2 is turned on and the switching element Q1 is turned off, as shown in FIG. 3 (b), the electric charge charged in the smoothing capacitor C0 is changed to the smoothing capacitor C0 → the capacitor C3 → the capacitor C1 → the choke coil. L1 → coupling capacitor C4 → switching element Q2 → discharged on the path of smoothing capacitor C0, and inductor L2 → capacitor C3 → capacitor C1 →
A current flows through a path from the discharge lamp FL, the capacitor C2 to the inductor L2, and the capacitor C3 is charged.

When the voltage Vc3 across the capacitor C3 becomes substantially equal to the voltage (Vdc-Vin) between the voltage Vdc across the smoothing capacitor C0 and the input voltage Vin, the smoothing capacitor C0
The inverter operation that operates with the power supply is eliminated, and FIG.
As shown in (c), the path of the AC power supply Vs → the rectifier DB → the capacitor C1 → the choke coil L1 → the coupling capacitor C4 → the switching element Q2 → the rectifier DB → the AC power supply Vs and the AC power supply Vs → the rectifier DB → the capacitor C1. → discharge lamp FL, capacitor C2 → inductor L2
The input current Id is drawn through the smoothing capacitor C0, the rectifier DB, and the path of the AC power supply Vs.
And the coupling capacitor C4 is charged. Thereafter, as shown in FIG. 3D, the AC power supply Vs → the rectifier D
B → Capacitor C1 → Choke coil L1 → Coupling capacitor C4 → Switching element Q2 → Rectifier DB
→ The input current Id is drawn in the path of the AC power supply Vs, and the discharge current of the smoothing capacitor C0 is reduced by the smoothing capacitor C0 → the inductor L2 → the discharge lamp FL and the capacitor C2.
→ Choke coil L1 → Coupling capacitor C4 →
The current flows through the path from the switching element Q2 to the smoothing capacitor C0, and the coupling capacitor C4 is charged.

Next, when both the switching elements Q1 and Q2 are turned off, as shown in FIG.
The rectifier DB → the capacitor C1 → the choke coil L1 → the coupling capacitor C4 → the parasitic diode (not shown) of the switching element Q1 → the smoothing capacitor C0 → the rectifier DB → the input current Id is drawn in the path of the AC power supply Vs, and the smoothing capacitor C0. Is charged, and the energy stored in the inductor L2 causes the inductor L2 →
A current flows through the discharge lamp FL, the capacitor C2, the choke coil L1, the coupling capacitor C4, the parasitic diode of the switching element Q1, and the inductor L2, and the coupling capacitor C4 is charged.

Thereafter, when the switching element Q1 is turned on and the switching element Q2 is turned off, as shown in FIG. 4 (b), the electric charge charged in the capacitor C3 is changed from the capacitor C3 → the inductor L2 → the discharge lamp FL, the capacitor C2 →
Discharge is performed through the path of the capacitor C1 → the capacitor C3 and the path of the capacitor C3 → the switching element Q1 → the coupling capacitor C4 → the choke coil L1 → the capacitor C1 → the capacitor C3. When the charge stored in the capacitor C3 becomes zero, a current flows through the diode D1 instead of the capacitor C3 as shown in FIG. 4C. Thereafter, as shown in FIG. 4D, the discharge current of the coupling capacitor C4 is changed to the coupling capacitor C4 → the choke coil L1 → the capacitor C1 → the diode D1 → the switching element Q1 → the coupling capacitor C4, and the coupling path. The current flows through the path of the capacitor C4 → the choke coil L1 → the discharge lamp FL, the capacitor C2 → the inductor L2 → the switching element Q1 → the coupling capacitor C4. As described above, in this circuit, after the charging operation of the capacitor C3 is completed, FIG.
In the mode shown in FIG. 4D and FIG. 4A, the input current Id is drawn from the AC power supply Vs.

By the way, in the conventional circuit, the current Ic1 related to the charging of the capacitor C3 increases at light load, so that the input current Id drawn from the AC power supply Vs increases, and as a result, the voltage across the smoothing capacitor C0 increases. There was a problem. In this circuit, as shown in FIG. 2B, the frequency characteristic of the current Ic1 includes an anti-resonance frequency f03 at which the current Ic1 is minimized.
From the frequency f1 to f2, the anti-resonance frequency f03
, The current Ic1 can be reduced similarly to the output of the inverter circuit INV. Therefore, the time required for charging the capacitor C3 increases, and the period during which the input current Id is drawn is shortened, so that the voltage Vdc across the smoothing capacitor C0 can be prevented from increasing.

In the circuit operation under light load, when the operating frequency f of the inverter circuit INV is increased, the current flowing through the inductor L2 increases, but the current Ic1 flowing through the capacitor C1 decreases. The operations shown in FIGS. 3 (c) and 4 (c) change to the operations shown in FIGS. 5 (a) and 5 (b), respectively, and the charging period of the capacitor C1 becomes longer. Therefore, the period during which the input current Id is drawn is shortened, and the input power is reduced. Therefore, it is possible to suppress an increase in the voltage Vdc across the smoothing capacitor C0. Here, when the inductance L2 of the inductor L2 is zero, that is, when the anti-resonance frequency f03 → ∞ according to the equation (1), the present circuit is the same as the conventional circuit, but the anti-resonance frequency f03 is a finite value. If it is, the operating frequency f of the inverter circuit INV at the time of light load is brought close to the anti-resonance frequency f03, so that the current Ic1 flowing through the capacitor C1 can be made smaller than that of the conventional circuit. Can be suppressed from rising. Therefore, a low withstand voltage element can be used for each element, and the manufacturing cost can be reduced. In addition, by setting the frequency width between the resonance frequency f01 on the low frequency side and the antiresonance frequency f03 to an appropriate value, the current I
The value of c1 can be changed, and the voltage Vdc across the smoothing capacitor C0 can be kept substantially constant at an arbitrary load output.

In the circuit of this embodiment, the coupling capacitor C4 is connected between the connection point of the switching elements Q1 and Q2 and the choke coil L4.
As shown in (5), the coupling capacitor C4 may be connected between the connection point of the diode D1 and the switching element Q1 and the inductor L2.

In the circuit of this embodiment, the load Z is connected in parallel with the capacitor C2. As shown in FIG. 7, the primary winding of the transformer T1 is connected in parallel with the capacitor C2. A load Z may be connected between both ends of the secondary winding of T1. Further, in the circuit of the present embodiment, the capacitor C2 is connected in series with the inductor L2. However, as shown in FIG. 8, the primary winding of the transformer T2 is connected in series with the inductor L2, A parallel circuit of the capacitor C2 and the load Z may be connected between both ends of the next winding.

Further, in the circuit of this embodiment, the choke coil L is connected between both ends of the high-potential side switching element Q1.
1 and a series circuit of the coupling capacitor C4 via a series circuit of the coupling capacitor C4. As shown in FIG. 9, the choke coil L1 and the coupling capacitor C4 are connected between both ends of the switching element Q1. The primary winding of the transformer T3 is connected through the series circuit of the above, and the series resonance circuit of the inductor L2 and the capacitor C2 is connected between both ends of the secondary winding of the transformer T3. You may make it connect. Also, in the circuit of FIG.
0, the transformer T3 is a leakage transformer, and the leakage inductance of the transformer T3 and the capacitor C
2 may form a resonance circuit.

(Embodiment 2) FIG. 11 is a circuit diagram of a power supply device according to this embodiment. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the circuit of FIG. 1 described in the first embodiment, the series resonance of the inductor L2 and the capacitor C2 is provided between both ends of the switching element Q1 on the high potential side via a series circuit of the choke coil L1 and the coupling capacitor C4. Although a circuit is connected and a load Z is connected in parallel with the capacitor C2, in the present embodiment, in the circuit of FIG.
A series resonance circuit of the inductor L2 and the capacitor C2 is connected between both ends of the switching element Q2 on the low potential side via a series circuit of the choke coil L1 and the coupling capacitor C4, and a load Z is connected in parallel with the capacitor C2. ing. Since the circuit of the present embodiment also performs the same operation as that of the first embodiment, the smoothing capacitor C
It is possible to suppress the voltage Vdc between both ends of 0 from increasing. Therefore, a low withstand voltage element can be used for each element, and the cost can be reduced.

(Embodiment 3) FIG. 12 is a circuit diagram of a power supply device according to this embodiment.

In the present embodiment, in the circuit shown in FIG. 1 described in the first embodiment, the inductor L2 and the inductor L2 are connected between both ends of the high-potential side switching element Q1 via a series circuit of the choke coil L1 and the coupling capacitor C4. A series circuit of the discharge lamp FL is connected, and a preheating capacitor C2 is connected between the non-power-supply-side terminals of both filament electrodes of the discharge lamp FL.
Are connected, and a series resonance circuit is formed by the inductor L2 and the capacitor C2.

In this circuit, similar to the circuit of the first embodiment,
Inverter circuit INV at light load (during preheating)
Is set to a frequency at which the current Ic1 involved in drawing in the input current Id becomes small and at a frequency near the resonance frequency f02 on the high frequency side. Voltage Vdc
Can be suppressed from increasing.

FIG. 13A shows the frequency characteristic of the filament current If of the discharge lamp FL, and FIG. 13B shows the frequency characteristic of the current Ic1 flowing through the capacitor C1, and FIG.
(C) shows a frequency characteristic of a lamp voltage (no-load secondary voltage) VLa applied between both ends of the discharge lamp FL. FIG.
Solid lines in (a) to (c) are characteristic curves when the discharge lamp FL is turned on, and dashed lines in FIGS. 13A to 13C are characteristic curves when the discharge lamp FL is preheated.

Here, at the operating frequency f1 at the time of lighting, the filament current If is equal to the upper limit im at the time of lighting the discharge lamp.
ax, and the current Ic1 involved in drawing in the input current Id is a current that can sufficiently suppress the boosting of the voltage Vdc across the smoothing capacitor C0.
Inductance of inductor L2 and capacitor C2
(I.e., the anti-resonance frequency f03), and at the operating frequency fpre at which the current Ic1 at the time of the preliminary preheating becomes a current that can sufficiently suppress the increase of the voltage Vdc across the smoothing capacitor C0. The filament current If is the current range A of the standard value of the discharge lamp FL.
And the circuit constants of the capacitors and inductors constituting the resonance circuit are designed so that the lamp voltage VLa falls within the upper limit value Vmax, and the frequency difference between the anti-resonance frequency f03 and the resonance frequency f02 on the high frequency side is designed. Is set.

For example, in the case where the filament current If during the pre-heating is small and is out of the predetermined current range A, the procedure for adjusting the filament current If by changing the resonance frequency will be described with reference to FIGS. This will be described with reference to FIG. FIG. 14A shows the frequency characteristics of the filament current If, FIG. 14B shows the frequency characteristics of the current Ic1 flowing through the capacitor C1, and FIG.
Lamp voltage applied across L (no load secondary voltage)
4 shows the frequency characteristics of VLa. 14 (a) to 14 (c).
The solid line in the middle is the characteristic curve before adjusting the resonance frequency,
14A to 14C are characteristic curves after adjusting the resonance frequency.

Here, the resonance frequency on the high frequency side is a value f02 '(f02') lower than the value f02 before the resonance frequency adjustment.
<F02) (that is, so that the difference between the two resonance frequencies becomes small), the circuit constant is designed such that the resonance frequency on the high frequency side approaches the anti-resonance frequency f03 before adjustment, so that the filament current If The minimum value becomes larger than before the adjustment. At this time, if the operating frequency at the time of the preheating is changed to a value fpre ′ (fpre ′ <fpre) lower than the value fpre before the resonance frequency adjustment,
The filament current If during the pre-heating is within the predetermined current range A, and the lamp voltage VLa is higher than the upper limit value Vm.
ax.

On the other hand, when the filament current If during the preheating is large or when the lamp voltage VLa is
FIG. 15 shows a procedure for adjusting the filament current If by changing the resonance frequency when the value exceeds max.
This will be described with reference to (a) to (c). FIG. 15A shows a frequency characteristic of the filament current If, and FIG.
Shows the frequency characteristics of the current Ic1 flowing through the capacitor C1, and FIG. 15C shows the frequency characteristics of the lamp voltage (no-load secondary voltage) VLa applied across the discharge lamp FL.
The solid lines in FIGS. 15A to 15C are characteristic curves before the resonance frequency is adjusted, and the dashed lines in FIGS. 15A to 15C are the characteristic curves after the resonance frequency is adjusted. It is.

Here, the resonance frequency on the high frequency side is a value f02 ″ (f02 ″) higher than the value f02 before the resonance frequency adjustment.
> F02) (ie, so that the difference between the two resonance frequencies becomes large), and the filament constant If is designed to keep the high-frequency resonance frequency away from the anti-resonance frequency f03 before adjustment. Is smaller than before the adjustment. At this time, if the operating frequency at the time of the preliminary preheating is changed to a value fpre ″ (fpre ″> fpre) higher than the value fpre before the resonance frequency adjustment, the filament current If at the time of the preliminary preheating falls within the predetermined current range A. And the lamp voltage VLa falls within the upper limit value Vmax.

Thus, the two resonance frequencies f01 and f01
02, the filament current I
Since f can be adjusted to be within the predetermined current range A, even when the load is a small-diameter discharge lamp whose lamp impedance is relatively high and whose upper limit is set to the filament current at the time of lighting. It is possible to design the filament current If with a capacitor preheating circuit, without adding elements such as a filament preheating transformer as in the case of using a filament inverter, and without increasing the cost due to an increase in elements. A circuit can be realized.

(Embodiment 4) FIG. 16 is a circuit diagram of a power supply device according to this embodiment.

In the present embodiment, in the circuit of the third embodiment, an inductor L2 and a capacitor C2 are connected between both ends of a high-potential side switching element Q1 via a series circuit of a choke coil L1 and a coupling capacitor C4.
, A power supply terminal of both filament electrodes of the discharge lamp FL is connected to both ends of the capacitor C2, and a preheating capacitor C2 'is connected between the non-power supply terminals of both filament electrodes of the discharge lamp FL. Are connected. The configuration other than the capacitors C2 and C2 'is the same as that of the third embodiment.

As described above, the capacitor constituting the resonance circuit together with the inductor L2 is divided into C2 and C2 ', and one of the capacitors C2' is used to preheat the filament. Can be improved in the degree of freedom in designing the filament current as compared with the case where is constituted by one capacitor C2.
The resonance frequency can be easily set as compared with the circuit of the third embodiment.

In this circuit, when the discharge lamp FL is removed, a current loop flowing through the inductor L2, the capacitors C2 and C2 'and the discharge lamp FL becomes a current loop flowing through the inductor L2, the capacitor C2 and the discharge lamp FL. Changes to FIG. 17A shows the current Ic1 when the discharge lamp FL is mounted.
FIG. 17B shows the frequency characteristics of the current Ic1 when there is no load. The solid line in FIG. 17A is a characteristic curve when the discharge lamp is turned on.
The dashed line in (a) is a characteristic curve at the time of pre-heating.

Here, when the discharge lamp FL is removed, the current Ic1
Is obtained from the characteristic curve shown in FIG.
The characteristic curve changes to the characteristic curve shown in FIG.
f02 changes to resonance frequencies f01 'and f02', respectively. The anti-resonance frequency f03 when the discharge lamp FL is mounted is determined by the inductor L2 and the capacitors C2 and C2 '. The anti-resonance frequency f03' when no load is applied is determined by the inductor L2 and the capacitor C2. Assuming that the capacitance is C2 ', the anti-resonance frequencies f03 and f03' are expressed by Expressions (2) and (3), respectively.

F03 = 1 / [2π ｛L2 (C2 + C2 ′)｝ ^1/2 ] (2) f03 ′ = 1 / {2π (L2 · C2) ^1/2 ｝ (3) By setting the operating frequency f of the inverter circuit INV when the discharge lamp FL is removed (at no load) to a frequency fNL substantially equal to the anti-resonant frequency f03 'at no load, Since the current Ic1 becomes almost zero and the period required for charging the capacitor C3 becomes longer, the period during which the input current Id is drawn can be made almost zero. C0
Can be suppressed from being raised.
Further, in this circuit, the oscillating operation is continued even when there is no load. Therefore, when the discharge lamp FL is mounted again, the discharge lamp F
L can be easily restarted and turned on, and the discharge lamp FL
It is possible to easily design a control circuit for restarting and lighting the discharge lamp FL at the time of re-installation.

(Embodiment 5) FIG. 18 is a circuit diagram of a power supply device according to this embodiment.

In the present embodiment, in the circuit of the third embodiment, the inductor L2 and the discharge lamp FL are connected in series between the both ends of the high-potential side switching element Q1 via a series circuit of the choke coil L1 and the coupling capacitor C4. In addition to connecting the circuit, a capacitor C21 is connected between the power supply side terminal of one filament electrode fa of the discharge lamp FL and the non-power supply side terminal of the other filament electrode fb to connect one filament electrode fa of the discharge lamp FL. A capacitor C22 is connected between the non-power supply terminal and the power supply terminal of the other filament electrode fb. Embodiment 3
The same components as those of the circuit of FIG.

As described in the fourth embodiment, when the capacitor constituting the resonance circuit is divided into two, if the capacitances of the divided capacitors C2 and C2 'are substantially equal, as in the present embodiment, two capacitors are used. The filament electrodes fa and fb may be independently preheated by the capacitors C22 and C21. In the circuit of FIG. 12, both filament electrodes are connected in series via a capacitor C2, whereas in the present circuit, two filament electrodes fa and fb are connected in parallel, so that the resistance component of the filament is reduced. When the filament current is the same, the filament loss can be reduced. In this circuit, the discharge lamp FL
Is removed and the inductor L2 and the capacitor C
Since there is no current loop flowing through the current lamps 21 and C22 and the discharge lamp FL, a no-load state can be detected from the presence or absence of a current flowing through this current loop.

FIG. 19A shows the frequency characteristic of the current Ic1 when the discharge lamp FL is mounted, and FIG.
Shows the frequency characteristic of the current Ic1 when there is no load. Note that the solid line in FIG. 19A is a characteristic curve when the discharge lamp is turned on, and the one-dot chain line in FIG. 19A is a characteristic curve during pre-heating. Here, when the discharge lamp FL is removed, the frequency characteristic of the current Ic1 changes from the frequency characteristic where two resonance frequencies f01 and f02 exist as shown in FIG. As shown in the figure, the frequency characteristic changes to such that only one resonance frequency f01 'exists. At this time, by setting the operating frequency f of the inverter circuit INV to be higher than the resonance frequency f01 'and to a frequency fNL at which the resonance of the resonance circuit becomes very weak, the current Ic1 relating to the charging of the capacitor C3 is reduced. Therefore, the time required for charging the capacitor C3 becomes longer. Therefore, the period during which the input current Id is drawn can be almost eliminated, and the boosting of the voltage Vdc across the smoothing capacitor C0 can be suppressed while maintaining the oscillation state.
Further, in this circuit, the oscillation state is maintained even when there is no load, so that when the discharge lamp FL is mounted again, the discharge lamp FL can be easily restarted and turned on.
It is possible to easily design a control circuit that restarts and turns on the discharge lamp FL when the lamp L is remounted.

As described above, in a circuit in which there is no current loop flowing through the inductor L2, the capacitors C21 and C22 and the discharge lamp FL when the discharge lamp FL is removed and no load is applied, the operating frequency of the inverter circuit INV when there is no load. By setting f to a frequency at which the resonance of the resonance circuit becomes very weak, the oscillation operation is maintained while the boosting of the voltage Vdc across the smoothing capacitor C0 is maintained even when no load is applied, and a standby state is set. be able to.

Also in the circuit of the third embodiment, there is no current loop flowing through the inductor L2, the capacitor C2 and the discharge lamp FL when there is no load, and the frequency characteristic of the current Ic1 when the discharge lamp FL is mounted and when there is no load. Is shown in FIG.
(B), the operating frequency f of the inverter circuit INV at the time of no load is set to a frequency at which the resonance of the resonance circuit becomes very weak.
Voltage Vdc across smoothing capacitor C0 even at no load
Oscillating operation can be continued while suppressing the step-up of the voltage, and a standby state can be achieved.

(Embodiment 6) FIG. 20 is a circuit diagram of a power supply device according to this embodiment.

In the present embodiment, in the circuit of the third embodiment, a diode D as a second diode is connected between the smoothing capacitor C0 and the low-potential-side DC output terminal of the rectifier DB.
2 and a capacitor C5 as a third capacitor is connected between a connection point between the series circuit of the choke coil L1 and the coupling capacitor C4 and the capacitor C1 and a DC output terminal on the low potential side of the rectifier DB. ing. Since the configuration other than the capacitor C5 and the diode D1 is the same as that of the circuit of the third embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

In the circuit of this embodiment, the third embodiment
Similarly to the above, the voltage Vdc across the smoothing capacitor C0 can be prevented from increasing at a light load, so that each element can be used with a low withstand voltage, and the cost can be reduced. Also, in this circuit, the filament current can be easily adjusted in the same manner as in the third embodiment. Therefore, even when a small-diameter fluorescent lamp is used as the discharge lamp FL, the filament current is set to a predetermined value by the capacitor preheating circuit. Value can be designed.

The operation of this circuit will now be described with reference to FIGS. 21 and 22.
This will be described with reference to FIG. Note that arrows in FIGS. 21 and 22 indicate paths through which current flows. 21 and 22, the control circuit 2 is omitted.

As shown in FIG. 21A, the capacitor C
When the switching elements Q1 and Q2 are both turned off in a state where the electric charge charged in 3 becomes zero, the AC power supply Vs → the rectifier DB → the diode D1 → the smoothing capacitor C0 → the parasitic diode of the switching element Q2 → the coupling capacitor C4 → The input current Id is drawn in the path of the choke coil L1 → the capacitor C5 → the rectifier DB → the AC power supply Vs, and the coupling capacitor C4 → the choke coil L1 → the capacitor C1 → the diode D1 → the smoothing capacitor C0 → the parasitic diode of the switching element Q2 → The path of the coupling capacitor C4, the coupling capacitor C4 → the choke coil L1 → the discharge lamp FL, the capacitor C2 → the inductor L2 → the smoothing capacitor C0 →
Current flows from the parasitic diode of the switching element Q2 to the path of the coupling capacitor C4, and the smoothing capacitor C0 is charged.

Thereafter, when the switching element Q2 is turned on and the switching element Q1 is turned off, as shown in FIG. 21 (b), the electric charge charged in the smoothing capacitor C0 is transferred to the smoothing capacitor C0 → the capacitor C3 → the capacitor C1 → the choke coil. L1 → coupling capacitor C4 → switching element Q2 → discharged on the path of smoothing capacitor C0, and the choke coil L1 → coupling capacitor C4 →
Switching element Q2 → Diode D2 → Capacitor C
5 → Current flows through the path of the choke coil L1, and due to the energy accumulated in the inductor L2, current flows through the path of the inductor L2 → capacitor C3 → capacitor C1 → discharge lamp FL, capacitor C2 → inductor L2. Charged.

When the voltage Vc3 across the capacitor C3 becomes substantially equal to the voltage (Vdc−Vin) between the voltage Vdc across the smoothing capacitor C0 and the input voltage Vin, the smoothing capacitor C0
As shown in FIG.
As shown in FIG. 1 (c), the input current Id is drawn in the path of AC power supply Vs → rectifier DB → capacitor C1 → discharge lamp FL, capacitor C2 → inductor L2 → smoothing capacitor C0 → diode D2 → rectifier DB → AC power supply Vs. At the same time, current flows through the path of the choke coil L1, the coupling capacitor C4, the switching element Q2, the capacitor C5, and the choke coil L1, and the smoothing capacitor C0 and the coupling capacitor C4 are charged.
Thereafter, as shown in FIG. 21 (d), the input current Id in the path of the AC power supply Vs → the rectifier DB → the capacitor C1 → the choke coil L1 → the coupling capacitor C4 → the switching element Q2 → the diode D2 → the rectifier DB → the AC power supply Vs. And the discharge current of the smoothing capacitor C0 is reduced by the smoothing capacitor C0 → the inductor L2 → the discharge lamp FL, the capacitor C2 → the choke coil L1 → the coupling capacitor C4 → the switching element Q2 → the smoothing capacitor C
The current flows along the path of 0, and the current flows through the path of the choke coil L1 → coupling capacitor C4 → switching element Q2 → diode D2 → capacitor C5 → choke coil L1 to charge the coupling capacitor C4.

Next, when both the switching elements Q1 and Q2 are turned off, as shown in FIG.
→ Rectifier DB → Capacitor C1 → Choke coil L1 →
Coupling capacitor C4 → parasitic diode of switching element Q1 → smoothing capacitor C0 → diode D2
→ The rectifier DB → the input current Id is drawn in the path of the AC power supply Vs, and the smoothing capacitor C0 is charged, and the inductor L2 → the discharge lamp FL, the capacitor C2 → the choke coil L1 → the coupling capacitor C4 → the switching element Q1. A current flows through the path of the parasitic diode → the inductor L2 and the path of the choke coil L1 → coupling capacitor C4 → parasitic diode of the switching element Q1 → smoothing capacitor C0 → diode D2 → capacitor C5 → the path of the choke coil L1. Is charged.

Thereafter, when the switching element Q1 is turned on and the switching element Q2 is turned off, as shown in FIG. 22B, the capacitor C3 → the inductor L2 → the discharge lamp F
L, capacitor C2 → capacitor C1 → capacitor C3
Current flows through the path of, the electric charge charged in the capacitor C3 is discharged, and the AC power supply Vs → the rectifier DB →
Capacitor C3 → switching element Q1 → coupling capacitor C4 → choke coil L1 → capacitor C5
→ Rectifier DB → Current flows on the path of AC power supply Vs, and when the charge charged in capacitor C3 becomes zero, FIG.
As shown in (c), a current flows through the diode D1 instead of the capacitor C3.

Thereafter, as shown in FIG. 22D, the discharge current of the coupling capacitor C4 is changed from the coupling capacitor C4 → the choke coil L1 → the capacitor C1 →
Path of diode D1 → switching element Q1 → coupling capacitor C4 and coupling capacitor C4
→ Choke coil L1 → Discharge lamp FL, condenser C2 →
The current flows through the path of the inductor L2 → the switching element Q1 → the coupling capacitor C4, and the AC power supply V
s → rectifier DB → diode D1 → switching element Q
1 → Coupling capacitor C4 → Choke coil L1
The input current Id is drawn through the path of the capacitor C5, the rectifier DB, and the AC power supply Vs. Thus, in this circuit,
Since the input current Id is drawn over substantially the entire period of one cycle of the pulsating voltage input from the rectifier DB, the peak value of the input current Id can be reduced, and the input current Id is connected between the AC power supply Vs and the rectifier DB. Input filter (not shown) can be reduced in size.

(Embodiment 7) FIG. 23 is a circuit diagram of a power supply device according to this embodiment.

This circuit is obtained by connecting a capacitor C6 as a fourth capacitor in parallel with the diode D2 in the circuit of the sixth embodiment. Note that the same components as those of the circuit of the sixth embodiment are denoted by the same reference numerals, and description thereof will be omitted. Also in this circuit, similarly to the circuit of the sixth embodiment, it is possible to suppress the voltage Vdc across the smoothing capacitor C0 from increasing at a light load, so that each element having a low withstand voltage can be used. Cost can be reduced. In addition, since the input current Id is drawn over substantially the entire period of one cycle of the pulsating voltage input from the rectifier DB, the peak value of the input current Id can be reduced, and between the AC power supply Vs and the rectifier DB. The connected input filter can be reduced in size. Further, in this circuit, the filament current can be easily adjusted in the same manner as in the third embodiment. Therefore, even when a small-diameter fluorescent lamp is used as the discharge lamp FL, the filament current is controlled by a capacitor preheating type circuit. Value can be designed.

(Embodiment 8) FIG. 24 is a circuit diagram showing a power supply device of this embodiment.

In this circuit, in the circuit of the third embodiment,
A series circuit of resistors R1 and R2 is connected between the connection point of the capacitor C1 and the choke coil L1 and the circuit ground, and a capacitor C7 is connected in parallel with the resistor R2 via a diode D3. After the potential V2 at the connection point of the capacitor C1 and the choke coil L1 is divided by the resistors R1 and R2, the voltage rectified and smoothed by the diode D3 and the capacitor C7 is input to the comparison detection circuit 3, and the comparison detection circuit 3 C7 and a predetermined threshold voltage V
Compare the magnitude relationship with th.

Here, when there is a load abnormality such as Emiless in the no-load state where the discharge lamp FL is removed or in the end-of-life state, the potential V2 at the connection point between the capacitor C1 and the choke coil L1 rises, and in response to the rise in the potential V2. The voltage across the capacitor C7 increases. Therefore, the comparison detection circuit 3 detects that the voltage between both ends of the capacitor C7 becomes larger than the threshold voltage Vth when the load is abnormal, and outputs a detection signal to the control circuit 2. In the control circuit 2, when the detection signal is input from the comparison detection circuit 3, the inverter circuit IN
V oscillation operation is stopped or the inverter circuit I
The operating frequency f of NV is changed to the voltage V across the smoothing capacitor C0.
Since the frequency is changed to a value that can suppress the rise of dc to cope with the abnormal load, the stress applied to each element can be reduced.

In this embodiment, since the potential V2 at the connection point between the capacitor C1 and the choke coil L2 becomes larger than the threshold voltage Vth, the comparison detection circuit 3 operates in the no-load state or the end-of-life state. Although a load abnormality is detected, as shown in FIG.
Compares the voltage Vdc across the smoothing capacitor C0 with a predetermined threshold voltage Vth.
dc is detected to be greater than the threshold voltage Vth,
A detection signal is output to the control circuit 3 so that the control circuit 3 stops the oscillating operation of the inverter circuit INV or sets the operating frequency f of the inverter circuit INV to a frequency that can suppress the rise of the voltage Vdc across the smoothing capacitor C0. May be changed.

(Embodiment 9) FIG. 26 is a circuit diagram showing a power supply device of this embodiment.

In this circuit, in the circuit of the third embodiment,
The inductor L2 is constituted by the primary winding of the transformer T4. After the current flowing through the secondary winding of the transformer T4 is rectified by the diode D3, the capacitor C7 is charged, and the comparison detection circuit 3 is connected to both ends of the capacitor C7. The magnitude relationship between the voltage and the predetermined threshold voltage Vth is compared.

Here, when there is no load when the discharge lamp FL is removed, there is no current loop flowing through the primary winding of the transformer T4, the discharge lamp FL and the capacitor C2.
No current flows through the primary winding of No. 4 and the capacitor C7 is no longer charged, and the voltage across the capacitor C7 becomes substantially zero. Therefore, the comparison detection circuit 3 detects that the voltage across the capacitor C7 becomes smaller than the threshold voltage Vth when there is no load, and outputs a detection signal to the control circuit 2. When the detection signal is input from the comparison detection circuit 3, the control circuit 2 stops the oscillation operation of the inverter circuit INV or suppresses the operating frequency f of the inverter circuit INV from increasing the voltage Vdc across the smoothing capacitor C0. Since the frequency is changed to such a value as possible to cope with the no-load state, the stress applied to each element can be reduced.

(Embodiment 10) FIG. 27 is a circuit diagram of a power supply device according to this embodiment.

In this circuit, in the circuit of the second embodiment,
The load Z is composed of a discharge lamp FL made of, for example, a fluorescent lamp, and a capacitor C2 is connected between the non-power-supply-side terminals of the discharge lamp FL. Then, the inductor L2 and the discharge lamp F
A series circuit of resistors R1 and R2 is connected between the connection point of L and the ground of the circuit, and a capacitor C7 is connected in parallel with the resistor R2 via a diode D3.
And the potential V3 at the connection point of the discharge lamp FL with the resistors R1 and R2.
After that, the voltage rectified and smoothed by the diode D3 and the capacitor C7 is input to the comparison detection circuit 3, and the comparison detection circuit 3 determines the magnitude relationship between the voltage across the capacitor C7 and the predetermined threshold voltage Vth. Compare.

Here, when there is a load abnormality such as Emiless in the no-load state where the discharge lamp FL is removed or in the end-of-life state, the potential V at the connection point between the inductor L2 and the discharge lamp FL is determined.
3 rises, and the voltage across the capacitor C7 rises in accordance with the rise in the potential V3. Therefore, the comparison detection circuit 3
It detects that the voltage across the capacitor C7 becomes larger than the threshold voltage Vth when the load is abnormal, and outputs a detection signal to the control circuit 2. When the detection signal is input from the comparison detection circuit 3, the control circuit 2 stops the oscillation operation of the inverter circuit INV or suppresses the operating frequency f of the inverter circuit INV from increasing the voltage Vdc across the smoothing capacitor C0. Since the frequency is changed to such a value as to cope with a load abnormality, the stress applied to each element can be reduced.

[0091]

As described above, the invention of claim 1 comprises a rectifier for rectifying an AC power supply, a smoothing capacitor connected between the DC output terminals of the rectifier via the first diode,
An inverter circuit that converts the voltage between both ends of the smoothing capacitor into a high-frequency voltage and supplies it to a load, a control circuit that controls the operating frequency of the inverter circuit, and one of the rectifiers via a series circuit of the coupling capacitor and the first inductor Feedback means for feeding back a part of the output of the inverter circuit to a connection point between the DC output terminal and the first diode; and a first capacitor connected in parallel to the first diode, the feedback means comprising: A second capacitor connected between a series circuit of the capacitor and the first inductor and one DC output terminal of the rectifier, wherein at least the inductor is connected between both ends of the second capacitor via the first diode. Connect a series resonance circuit including a capacitor, and in parallel with the impedance element included in the series resonance circuit. The load is connected, and at the time of a light load, the control circuit performs control so that the operating frequency of the inverter circuit approaches an anti-resonance frequency at which the current value of the current flowing to the load and the feedback means is minimized. When the voltage across the first capacitor is substantially equal to the difference between the voltage across the smoothing capacitor and the input voltage from the rectifier, the input current is drawn. Therefore, the input current is reduced by the current flowing through the feedback means associated with charging the first capacitor. Is determined, the control circuit brings the operating frequency of the inverter circuit closer to the anti-resonance frequency at a light load, thereby reducing the current flowing through the feedback means and increasing the time required for charging the first capacitor. The input current pull-in period can be shortened, and the voltage across the smoothing capacitor Since it is possible to reduce such stress, it is possible to use a low-voltage to each element, there is an effect that it is possible to reduce the cost.

According to a second aspect of the present invention, there is provided a rectifier for rectifying an AC power supply, a smoothing capacitor connected between the DC output terminals of the rectifier via a first diode, and converting a voltage across the smoothing capacitor into a high-frequency voltage. Circuit for controlling the operating frequency of the inverter circuit, and a connection point between one DC output terminal of the rectifier and the first diode via a series circuit of the coupling capacitor and the first inductor. And a first capacitor connected in parallel to a first diode, the feedback unit comprising: a series circuit of a coupling capacitor and a first inductor; A second capacitor connected between one of the DC output terminals of the rectifier, the coupling capacitor and the first capacitor; A series resonance circuit including at least an inductor and a capacitor is connected between a connection point between the series circuit of the inductor and the second capacitor and the other DC output terminal of the rectifier, and an impedance element included in the series resonance circuit The control circuit controls the inverter so that the operating frequency of the inverter circuit approaches an anti-resonance frequency that minimizes the value of the current flowing through the load and the feedback means when the load is light. When the voltage across the first capacitor becomes substantially equal to the difference between the voltage across the smoothing capacitor and the input voltage from the rectifier, the input current is drawn.
Since the input current pull-in period is determined by the current flowing through the feedback means relating to the charging of the first capacitor, the control circuit reduces the current flowing through the feedback means by bringing the operating frequency of the inverter circuit close to the anti-resonance frequency at a light load. It is possible to shorten the period required for charging the first capacitor by shortening the period, shorten the period for drawing the input current, suppress the voltage increase across the smoothing capacitor at light load, and reduce the stress applied to each element. Therefore, it is possible to use a device having a low withstand voltage for each element, and it is possible to reduce the cost.

According to a third aspect of the present invention, in the first or second aspect of the present invention, there are two resonance frequencies in the frequency characteristics of the current flowing through the load and the feedback means, and the control circuit sets the operating frequency of the inverter circuit to a low frequency. The control is performed between the resonance frequency on the side and the anti-resonance frequency.

According to a fourth aspect of the present invention, in the first or second aspect, the control circuit controls the operating frequency of the inverter circuit so that the current flowing through the feedback means at a light load is smaller than at the rated load. And reducing the current flowing through the feedback means when the load is light, thereby increasing the time required for charging the first capacitor to reduce the input current pulling period. Can be shortened, and it is possible to suppress an increase in the voltage across the smoothing capacitor at a light load.

According to a fifth aspect of the present invention, in the first or second aspect of the present invention, there are two resonance frequencies in the frequency characteristics of the current flowing through the load and the feedback means, and the load has a discharge lamp having a filament electrode at both ends. A capacitor for preheating is connected between the non-power-supply-side terminals of both filament electrodes so that a current equal to or less than the upper limit value of the filament current when the discharge lamp is turned on. As well as being within the current range required for preheating, the voltage across the discharge lamp is less than or equal to a predetermined upper limit, and the current flowing through the feedback means has a current value corresponding to the power consumption during preheating. The frequency difference between the resonance frequency and the anti-resonance frequency is set, and by setting the resonance frequency and the anti-resonance frequency on the high frequency side, the capacitor preheating method Since the preheating current during the preheating can be easily adjusted even on the road, there is no need to install a filament inverter to preheat the filament or add an element such as a transformer for preheating, reducing the cost of the preheating circuit. There is an effect that can be.

According to a sixth aspect of the present invention, in the invention of the fifth aspect, when the filament current during the preheating is smaller than a current range necessary for the preheating, the difference between the resonance frequency on the high frequency side and the antiresonance frequency is reduced. It is characterized in that it is set to be small, the minimum value of the current can be increased by reducing the frequency difference between the resonance frequency on the high frequency side and the antiresonance frequency, and the required filament current is increased by increasing the filament current. There is an effect that the current can be set within the current range.

According to a seventh aspect of the present invention, in the invention of the fifth aspect, when the filament current during the preheating is larger than the current range necessary for the preheating, or when the voltage across the discharge lamp during the preheating is the predetermined upper limit value If higher, the difference between the resonance frequency on the high frequency side and the anti-resonance frequency is set to be large, and the difference between the resonance frequency on the high frequency side and the anti-resonance frequency is increased. As a result, the minimum value of the current can be reduced, and there is an effect that the filament current can be reduced to be within a required current range.

According to an eighth aspect of the present invention, in the first or second aspect of the present invention, a second diode is connected between the smoothing capacitor and the other DC output terminal of the rectifier, and the coupling capacitor and the first inductor are connected. A third capacitor is connected between a connection point between the series circuit and the second capacitor and the other DC output terminal of the rectifier, and a fourth capacitor is connected in parallel with the second diode. By providing a current path through the third and fourth capacitors and the second diode, the input current can be drawn over substantially the entire period of one cycle of the input voltage, thereby reducing the peak value of the input current. Can be
There is an effect that the input filter connected between the AC power supply and the rectifier can be reduced in size.

According to a ninth aspect of the present invention, in the first or second aspect, the load comprises a discharge lamp having a filament electrode at both ends, and a series circuit of a coupling capacitor and a first inductor, and a second capacitor. The potential of the connection point is compared with a predetermined threshold voltage, and when the discharge lamp is unloaded or abnormal, it is detected that the potential of the connection point becomes higher than the threshold voltage. The control circuit operates the inverter circuit at such a frequency that the voltage across the smoothing capacitor can be suppressed from being boosted when a detection signal is input from the comparison detection circuit. When the comparison and detection circuit detects when the discharge lamp is unloaded or abnormal, the control circuit controls the operating frequency of the inverter circuit and the voltage across the smoothing capacitor increases. Since suppressed, because it is possible to reduce the stress on each element, it is possible to use a low-voltage to each element, there is an effect that it is possible to reduce the cost.

According to a tenth aspect of the present invention, in the first or second aspect, the load comprises a discharge lamp having a filament electrode at both ends, and when the discharge lamp is removed, the current loop is eliminated in the series resonance circuit. In this case, the second inductor is constituted by a primary winding of a transformer, a current-to-voltage converter is provided for detecting a current flowing through the secondary winding of the transformer, and generating a voltage corresponding to the current. Comparing the output voltage of the converter with a predetermined threshold voltage, and outputting a detection signal to the control circuit when the output voltage of the current-voltage converter is lower than the threshold voltage when the discharge lamp is not loaded. A detection circuit is provided, and the control circuit, when a detection signal is input from the comparison detection circuit, operates the inverter circuit at such a frequency that the resonance of the resonance circuit becomes weaker with the discharge lamp removed. When the comparison detection circuit detects that the discharge lamp is not loaded, the control circuit controls the operating frequency of the inverter circuit so that the resonance of the resonance circuit is weakened, so that the voltage across the smoothing capacitor increases. Can be suppressed and the stress applied to each element can be reduced. Therefore, each element can be used with a low withstand voltage, and the cost can be reduced.

According to an eleventh aspect of the present invention, in the first or second aspect, the load comprises a discharge lamp having a filament electrode at both ends, and a current loop is formed in the series resonance circuit even when the discharge lamp is removed. When the discharge lamp is removed, the control circuit operates the inverter circuit at a frequency substantially equal to the anti-resonance frequency such that the current value of the current flowing through the feedback means when the discharge lamp is removed is minimized. The control circuit operates the inverter circuit at a frequency substantially equal to the anti-resonance frequency when there is no load, so the voltage across the smoothing capacitor is suppressed from increasing and the stress on each element is reduced. Therefore, it is possible to use a device having a low withstand voltage for each element, and it is possible to reduce costs.

According to a twelfth aspect of the present invention, in accordance with the first or second aspect of the present invention, the load comprises a discharge lamp having a filament electrode at both ends, and compares the voltage between both ends of the smoothing capacitor with a predetermined threshold voltage. And a comparison detection circuit for detecting that the voltage between both ends becomes higher than the threshold voltage when the discharge lamp is unloaded or abnormal, and outputting a detection signal to a control circuit. When the detection signal is input from the inverter, the inverter circuit operates at a frequency that can suppress the voltage increase across the smoothing capacitor, and the comparison detection circuit detects when the discharge lamp is unloaded or abnormal. Then, since the control circuit controls the operating frequency of the inverter circuit and suppresses the voltage increase across the smoothing capacitor, can the stress applied to each element be reduced? , It is possible to use a low-voltage to each element, there is an effect that it is possible to reduce the cost.

[Brief description of the drawings]

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

FIGS. 2A and 2B are diagrams showing frequency characteristics of a current flowing in each part of the above.

FIGS. 3 (a) to 3 (d) are diagrams illustrating the operation of the above.

FIGS. 4A to 4D are diagrams for explaining the operation of the above.

FIGS. 5A and 5B are diagrams illustrating the operation of the above.

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

FIG. 7 is a circuit diagram showing another power supply device according to the first embodiment;

FIG. 8 is a circuit diagram showing still another power supply device according to the first embodiment.

FIG. 9 is a circuit diagram showing still another power supply device according to the first embodiment;

FIG. 10 is a circuit diagram showing another power supply device according to the first embodiment;

FIG. 11 is a circuit diagram illustrating a power supply device according to a second embodiment.

FIG. 12 is a circuit diagram showing a power supply device according to a third embodiment.

13A is a diagram showing a frequency characteristic of a filament current of the above, FIG. 13B is a diagram showing a frequency characteristic of a current Ic1 flowing through a capacitor C1, and FIG. 13C is a diagram showing a frequency characteristic of a lamp voltage. FIG.

14A is a diagram showing a frequency characteristic of a filament current of the above, FIG. 14B is a diagram showing a frequency characteristic of a current Ic1 flowing through a capacitor C1, and FIG. 14C is a diagram showing a frequency characteristic of a lamp voltage. FIG.

15A is a diagram showing a frequency characteristic of a filament current of the above, FIG. 15B is a diagram showing a frequency characteristic of a current Ic1 flowing through a capacitor C1, and FIG. 15C is a diagram showing a frequency characteristic of a lamp voltage. FIG.

FIG. 16 is a circuit diagram illustrating a power supply device according to a fourth embodiment.

17A and 17B show frequency characteristics of a current Ic1 flowing in the power supply device, where FIG. 17A shows frequency characteristics when a discharge lamp is mounted, and FIG.
FIG. 4 is a diagram showing frequency characteristics at the time of no load.

FIG. 18 is a circuit diagram illustrating a power supply device according to a fifth embodiment.

19A and 19B show frequency characteristics of a current Ic1 flowing in the power supply device of the above, where FIG.
FIG. 4 is a diagram showing frequency characteristics at the time of no load.

FIG. 20 is a circuit diagram illustrating a power supply device according to a sixth embodiment.

FIGS. 21A to 21D are diagrams for explaining the operation of the above.

FIGS. 22A to 22D are diagrams illustrating the operation of the above.

FIG. 23 is a circuit diagram showing a power supply device according to a seventh embodiment.

FIG. 24 is a circuit diagram showing a power supply device according to an eighth embodiment.

FIG. 25 is a circuit diagram showing another power supply device according to the embodiment.

FIG. 26 is a circuit diagram showing a power supply device according to a ninth embodiment.

FIG. 27 is a circuit diagram showing a power supply device according to a tenth embodiment.

FIG. 28 is a circuit diagram showing a conventional power supply device.

FIG. 29 is a waveform chart of each part of the power supply device,
(A) is a waveform diagram of the input voltage Vin, and (b) is a waveform diagram of the input current Iin.

FIG. 30 is a waveform diagram of each part of the power supply device,
3A is a waveform diagram illustrating a voltage across the impedance element Z1, FIG. 3B is a waveform diagram illustrating a voltage across the capacitor C3, and FIG. 3C is a waveform diagram illustrating a voltage across the load circuit 1.

FIG. 31 is a specific circuit diagram showing a conventional power supply device.

[Explanation of symbols]

 2 Control circuit C0 Smoothing capacitor C1 to C3 Capacitor C4 Coupling capacitor D1 Diode DB Rectifier INV Inverter circuit L1 Choke coil L2 Inductor Q1, Q2 Switching element Z Load

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K072 AA02 BA04 BB01 BC01 BC02 BC03 DB03 DD04 EA02 EB05 EB06 GA03 GB12 GC04 HA06 HB03 5H007 AA00 BB03 CA02 CB04 CB12 CC03 DA03 DA05 DB01 DC02 DC04 DC05 EA05

Claims (12)

[Claims] 1. A rectifier for rectifying an AC power supply, a smoothing capacitor connected between a DC output terminal of the rectifier via a first diode, and a voltage across the smoothing capacitor converted to a high-frequency voltage and supplied to a load. An inverter circuit, a control circuit for controlling the operating frequency of the inverter circuit, and an output of the inverter circuit connected to one of the DC output terminals of the rectifier and the first diode via a series circuit of the coupling capacitor and the first inductor. And a first capacitor connected in parallel to the first diode, the feedback means comprising: a series circuit of a coupling capacitor and a first inductor; A second capacitor connected between the second capacitor and the output terminal; In addition, a series resonance circuit including an inductor and a capacitor is connected, and a load is connected in parallel with the impedance element included in the series resonance circuit. A power supply device which controls an operating frequency of an inverter circuit to be close to an anti-resonance frequency which is minimized. 2. A rectifier for rectifying an AC power supply, a smoothing capacitor connected between a DC output terminal of the rectifier via a first diode, and a voltage across the smoothing capacitor converted to a high-frequency voltage and supplied to a load. An inverter circuit, a control circuit for controlling the operating frequency of the inverter circuit, and an output of the inverter circuit connected to one of the DC output terminals of the rectifier and the first diode via a series circuit of the coupling capacitor and the first inductor. And a first capacitor connected in parallel to the first diode, the feedback means comprising a series circuit of a coupling capacitor and a first inductor, and a direct current of one side of a rectifier. A series circuit of a coupling capacitor and a first inductor, comprising a second capacitor connected between the first capacitor and the output terminal; A series resonance circuit including at least an inductor and a capacitor is connected between a connection point with the second capacitor and the other DC output terminal of the rectifier, and a load is connected in parallel with the impedance element included in the series resonance circuit. A power supply device, wherein the control circuit controls the operation frequency of the inverter circuit to be close to an anti-resonance frequency at which a current value of a current flowing through the load or the feedback unit is minimized at a light load. 3. The frequency characteristic of the current flowing through the load and the feedback means has two resonance frequencies, and the control circuit controls the operation frequency of the inverter circuit between the low-frequency side resonance frequency and the anti-resonance frequency. The power supply device according to claim 1, wherein: 4. The power supply according to claim 1, wherein the control circuit controls the operating frequency of the inverter circuit so that a current flowing through the feedback means at a light load becomes smaller than at a rated load. apparatus. 5. The frequency characteristic of the current flowing through the load and the feedback means has two resonance frequencies. The load comprises a discharge lamp having a filament electrode at both ends, and is provided between the non-power-supply-side terminals of both filament electrodes. A capacitor for preheating is connected such that a current equal to or less than the upper limit of the filament current when the discharge lamp is turned on.
While the filament current is within the current range necessary for preheating, the voltage across the discharge lamp is equal to or less than a predetermined upper limit, and the current flowing through the feedback means has a current value corresponding to the power consumption during preheating. The power supply device according to claim 1, wherein a difference between a resonance frequency on the high frequency side and an anti-resonance frequency is set. 6. When the filament current during the preheating is smaller than the current range necessary for the preheating, the difference between the resonance frequency on the high frequency side and the antiresonance frequency is set to be small. The power supply device according to claim 5. 7. When the filament current at the time of preheating is larger than the current range necessary for preheating, or when the voltage across the discharge lamp at the time of preheating is higher than a predetermined upper limit, the resonance frequency on the high frequency side is changed. The power supply device according to claim 5, wherein a difference between the anti-resonance frequency and the anti-resonance frequency is set to be large. 8. A second diode is connected between the smoothing capacitor and the other DC output terminal of the rectifier, and a series circuit of the coupling capacitor and the first inductor is connected to the second diode.
A third capacitor is connected between a connection point of the rectifier and the other DC output terminal of the rectifier, and a fourth capacitor is connected in parallel with the second diode. 3. The power supply device according to 1 or 2. 9. The load comprises a discharge lamp having a filament electrode at both ends, a coupling capacitor and a first capacitor.
The potential of the connection point between the series circuit of the inductor and the second capacitor is compared with a predetermined threshold voltage, and when the discharge lamp is not loaded or abnormal, the potential of the connection point is higher than the threshold voltage. The detection circuit outputs a detection signal to the control circuit, and the control circuit suppresses the voltage rise across the smoothing capacitor when the detection signal is input from the comparison detection circuit. 3. The power supply device according to claim 1, wherein the inverter circuit is operated at a frequency as high as possible. 10. The load comprises a discharge lamp having a filament electrode at both ends. If the series resonance circuit has no current loop when the discharge lamp is removed, the second inductor is connected to a primary winding of a transformer. From the transformer 2
A current-to-voltage converter for detecting a current flowing in the next winding and generating a voltage corresponding to the current is provided, and the output voltage of the current-to-voltage converter is compared with a predetermined threshold voltage to determine the level of the discharge lamp. A comparison detection circuit is provided for outputting a detection signal to the control circuit when the output voltage of the current-to-voltage conversion means becomes lower than the threshold voltage during no load, and the control circuit releases when the detection signal is input from the comparison detection circuit. The power supply device according to claim 1 or 2, wherein the inverter circuit is operated at a frequency at which resonance of the resonance circuit becomes weaker in a state where the lamp is removed. 11. The control circuit according to claim 1, wherein said load comprises a discharge lamp having a filament electrode at both ends. When a current loop is formed in the series resonance circuit even when the discharge lamp is removed, the control circuit determines whether the discharge lamp has been removed. 3. The inverter circuit according to claim 1, wherein the inverter circuit is operated at a frequency substantially equal to the anti-resonance frequency such that the current value of the current flowing through the feedback means becomes minimum when the discharge lamp is removed. Power supply. 12. The load comprises a discharge lamp having a filament electrode at both ends, and compares the voltage between the both ends of the smoothing capacitor with a predetermined threshold voltage to determine whether the discharge lamp has no load or abnormal when the load is unloaded or abnormal. Is provided above the threshold voltage, and a comparison detection circuit is provided for outputting a detection signal to the control circuit. When the detection signal is input from the comparison detection circuit, the control circuit detects the voltage across the smoothing capacitor. 3. The power supply device according to claim 1, wherein the inverter circuit is operated at a frequency capable of suppressing the voltage from being increased.