JP2000245159A - Power supply equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply equipment which has little distortion in input current and has a small peak factor of the current in a load circuit and is constituted of a small number of components. SOLUTION: Between DC output terminals of a rectifier DB for rectifying an AC power supply AC, a capacitor C2 of a relatively small capacity is connected via a diode D11. To a connection between the rectifier DB and the diode D11, one end of a capacitor C0 of a relatively large capacity is connected. A series circuit of the capacitor C0, the diode D11, and the capacitor C2 is connected in parallel by a series circuit of a pair of switching elements Q1, Q2 which are alternatedly turned on and off at high frequencies, Between a connection between the capacitor C2 and the diode D11 and a connection between the switching elements Q1, Q2, a primary winding of a transformer T1 which is a leakage transformer is inserted. A load circuit 1 is connected to a secondary winding of the transformer T1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for converting a DC voltage obtained by rectifying and smoothing an AC power supply to a high frequency and supplying it to a load.

[0002]

2. Description of the Related Art Conventionally, a power supply device having a circuit configuration as shown in FIG.
-285933).

This power supply device includes a rectifier DB for full-wave rectification of an AC power supply AC such as a commercial power supply, and a capacitor C2 having a relatively small capacity is connected between the DC output terminals of the rectifier DB. Rectifier DB comprises a diode bridge. A capacitor C0 having a relatively large capacity is connected in series to the capacitor C2. A series circuit of a pair of switching elements Q1 and Q2 is connected in parallel to the series circuit of the capacitors C0 and C2, and a leakage transformer is provided between the connection point of the capacitors C0 and C2 and the connection point of the switching elements Q1 and Q2. The primary winding of the transformer T1 is inserted.
The load circuit 1 is connected to the secondary winding of the transformer T1.
Here, as the load circuit 1, a discharge lamp (fluorescent lamp) FL in which one end of a filament is connected to both ends of a secondary winding of the transformer T1 and a non-power supply end of each filament of the discharge lamp FL are connected. A capacitor provided with a preheating or resonance capacitor C1 is used, and a resonance circuit is formed by the leakage inductance of the transformer T1 and the capacitor C1. Also, the switching element Q
1 and Q2 use bipolar transistors, and diodes D1 and D2 are connected in anti-parallel, respectively. The switching elements Q1 and Q2 are alternately turned on and off at a switching frequency sufficiently higher than the power supply frequency by a control circuit (not shown).

The operation of this circuit configuration in a steady state will be described. Since the capacitor C0 is charged in the steady state, when the switching element Q1 is turned on, FIG.
6, the capacitor C0 → transformer T1
Current flows through the path of the primary winding → the switching element Q1 → the capacitor C0, and power is supplied to the load circuit 1 via the transformer T1. Next, when the switching element Q1 is turned off, as shown by the broken line in FIG. 17, the energy stored in the transformer T1 is changed to the primary winding of the transformer T1.
The energy is discharged through the path of the diode D2 → the capacitor C2 → the primary winding of the transformer T1, and the energy of the transformer T1 is transferred to the capacitor C2. During this period, the capacitor C2
Voltage across V _C2 of the is increased by resonance of the leakage inductance of the transformer T1 (see FIG. 21 (c)).

Thereafter, when the switching element Q2 is turned on, the leakage inductance of the transformer T1 and the resonance action of the capacitors C1 and C2 cause the primary winding of the capacitor C2 → the switching element Q2 → the transformer T1 as shown by the broken line in FIG. A resonance current flows through the path from the line to the capacitor C2, and power is supplied to the load circuit 1 via the transformer T1. At this time, since the direction of the current flowing through the primary winding of the transformer T1 is opposite to the direction when the switching element Q1 is on, an alternating high-frequency voltage can be applied to the load circuit 1.

When the charge of the capacitor C2 is released in the state of FIG. 18 and the voltage V _C2 across the capacitor C2 decreases to the output voltage of the rectifier DB as shown in FIG.
As indicated by a broken line in FIG. 9, a current flows through the route of the rectifier DB → the switching element Q2 → the primary winding of the transformer T1 → the rectifier DB. That is, the input current Iin flows from the AC power supply AC to the rectifier DB.

Thereafter, when the switching element Q2 is turned off, the energy stored in the transformer T1 is changed to the state shown in FIG.
As indicated by a broken line at 0, the light is emitted through the path of the primary winding of the transformer T1, the capacitor C0, the diode D1, and the primary winding of the transformer T1. In this power supply, the capacitor C
Since energy is stored in the transformer T1 from not only the AC power source AC but also the AC power supply AC, a relatively large energy can be stored in the transformer T1. Further, the capacitor C0
Are given by the energy stored in the transformer T1. By such an operation, the positive electrode of the capacitor C0 provided for smoothing corresponds to the negative electrode of the DC output terminal of the rectifier DB. Here, FIG. 19 and FIG.
0, the switching element Q2, the transformer T1, and the diode D1 are of a polarity reversal type (Buck Boost
(Type) chopper circuit.

When the energy stored in the transformer T1 is released in the state shown in FIG. 20, the operation returns to the state in which the electric charge is released from the capacitor C0 as shown in FIG. 16, and the operations in FIGS. 16 to 20 are repeated. To supply the alternating high-frequency power to the load circuit 1.

FIG. 21 shows operation waveforms of each part in each state shown in FIGS. FIG. 7A shows a signal voltage input to the base of the switching element Q1,
V corresponds to the off state of the switching element Q1. FIG. 4B shows a current I _T1 flowing through the primary winding of the transformer T1, and FIG. 4C shows a power supply voltage Vs of the AC power supply AC and a capacitor C.
2 (d) shows the relationship between the voltage V _{C2 of the} two terminals, and FIG.
5 shows the input current Iin. Further, a to e show states corresponding to FIGS. As is clear from FIG. 21, there is a period during which the input current Iin flows from the AC power supply AC while the switching elements Q1 and Q2 are repeatedly turned on and off once. The switching elements Q1, Q2
The switching frequency of the AC power supply AC during one cycle
Are set to such an extent that the power supply voltage Vs can be regarded as constant.

By such an operation, the operation waveform of each part of the circuit of FIG. 15 becomes as shown in FIG. 22 during one cycle of the voltage change of the AC power supply AC. 2A shows the waveform of the voltage V _C2 across the capacitor C2, FIG. 2B shows the current I _T1 flowing through the primary winding of the transformer _T1 , and FIG. 2C shows the input current Iin to the rectifier DB. (D) is a current I _La flowing through the discharge lamp FL provided in the load circuit 1.

Incidentally, although not shown in FIG.
In the circuit that supplies the high frequency power of the type
In order to prevent high frequency components from being mixed into the power supply AC,
Filter for blocking high frequency between power supply AC and rectifier DB
It is common to insert circuits. This
By providing such a filter circuit,
The input current Iin has a sinusoidal waveform as shown in FIG.
It takes shape. That is, the input current I shown in FIG.
only the envelope component of the AC power
An input current substantially proportional to the pressure Vs is obtained. Also input
In the current waveform, the capacitance of the capacitor C2 is an important factor.
You. For example, the voltage V across the capacitor C2 _C2Large amplitude
When it becomes difficult, as shown in FIG.
Input current Iin from the filter circuit
Polarity is inverted during the period of
You. The voltage V across the capacitor C2_C2Small amplitude
When it becomes difficult, as shown in FIG.
A pause occurs in the input current Iin to the filter. Either
In the case of, noise is mixed into the AC power supply AC.
As shown in FIG. 23B, the input current Iin is substantially proportional to the power supply voltage.
The capacity of the capacitor C2 is set appropriately so that
Not only reduces input current harmonics, but also
The power factor also increases.

The above publication also discloses a circuit as shown in FIG. The circuit of FIG. 24 is different from the circuit of FIG. 15 in that a capacitor C0 having a relatively large capacity is connected in series to the positive electrode side of the capacitor C2, and the operation is almost the same as the circuit of FIG.

[0013]

However, FIG.
In the conventional configuration shown in FIG. 21, the voltage V _C2 across the capacitor C2 increases due to the resonance operation during the off period of the switching element Q1 shown in FIG. 21 (see FIG. 21C).
As shown in (a), although the absolute value of the voltage of the AC power supply AC rises significantly during a period (valley), the voltage applied to the switching element Q1 is the voltage of the capacitor C2 and the voltage of the capacitor C0. Therefore, there is a problem that a switching element having a high withstand voltage is required as the switching element Q1.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to reduce input current harmonics, reduce the crest factor of current flowing in a load circuit, further reduce the number of components, and to reduce the number of components. It is an object of the present invention to provide a power supply device capable of lowering the withstand voltage of the power supply.

[0015]

According to a first aspect of the present invention, there is provided a rectifier for rectifying an AC power supply, and a first series circuit including a first diode and a first capacitor connected between the DC output terminals of the rectifier. A second capacitor having one end connected to a connection point between the rectifier and the first diode and having a capacity sufficiently larger than the capacity of the first capacitor; and both ends of the first series circuit via the second capacitor. A second series circuit of first and second switching elements connected between the first and second switching elements and alternately turned on and off at a frequency sufficiently higher than the frequency of the AC power supply; A primary winding is provided between a second diode and a third diode through which currents in opposite directions flow, and a connection point between the first diode and the first capacitor and a connection point between the first and second switching elements. Insertion And a transformer for providing a secondary output to the load circuit, wherein the first diode is inserted between the first capacitor and the second capacitor, so that the first Since the sum of the voltage across the first capacitor and the voltage across the second capacitor is not applied to the first switching element during the off period of the switching element, the withstand voltage of the first switching element can be reduced. it can. Further, during the period when the first switching element is on, the rectifier, the second capacitor, the first
Since the current flows through the path of the switching element, the primary winding of the transformer, the first capacitor, and the rectifier, the voltage of the first capacitor during the period in which the absolute value of the voltage of the AC power supply is low is reduced, and the primary It is possible to make the peak value of the voltage substantially constant over one cycle of the AC power supply,
The crest factor of the current flowing through the load circuit can be reduced.
In addition, during the period when the second switching element is on, a current flows through the rectifier, the first diode, the primary winding of the transformer, the second switching element, and the rectifier. The input current flows through different paths during the ON period of each of the switching elements, and the input current harmonics can be reduced by appropriately setting the capacity of the first capacitor. In addition, since only the first diode is added as the number of parts, the above object can be achieved with a relatively small number of parts.

According to a second aspect of the present invention, in the first aspect of the present invention, a control circuit capable of adjusting the on / off switching frequency of the first and second switching elements is provided.
By changing the switching frequency, the power supplied to the load circuit can be adjusted.

According to a third aspect of the present invention, in the first or second aspect of the present invention, since a control circuit capable of adjusting the on-periods of the first and second switching elements is provided, the on-period of the switching elements is changed. Thus, the power supplied to the load circuit can be adjusted.

According to a fourth aspect of the present invention, in the third aspect of the present invention, when the control circuit reduces the power consumption of the load circuit, the control circuit performs the second switching with respect to the sum of the ON period and the OFF period of the second switching element. Since the ratio of the ON period of the element is reduced, the power supplied to the load circuit and the input current can be adjusted, and the voltage across the second capacitor can be prevented from abnormally increasing.

According to a fifth aspect of the present invention, in the first aspect of the present invention, a voltage detecting means for detecting a voltage between both ends of the second capacitor is provided, and the first and the second switching are performed based on a voltage detected by the voltage detecting means. Since a control circuit for controlling at least one of a switching frequency for turning on and off the element and an on-period is provided, when the voltage across the second capacitor rises abnormally, the operation is stopped or the output to the load circuit is stopped. , It is possible to avoid stress on the circuit components. Further, if the voltage across the second capacitor is controlled to be kept substantially constant, the current supplied to the load circuit will be kept substantially constant, and stable operation of the load circuit can be expected. In particular, when the load circuit includes a discharge lamp, a light output with less flicker can be obtained.

According to a sixth aspect of the present invention, in the first aspect of the present invention, since a third capacitor connected in parallel to the first diode is provided, the first switching element is turned on during the period when the first switching element is on. Next winding, third capacitor, second
Capacitor, first switching element, transformer 1
A period for charging the third capacitor in the path of the secondary winding is provided, and the primary winding of the rectifier, the second capacitor, the first switching element, and the transformer is provided while the first switching element is on. , The period during which current flows through the path of the first capacitor and the rectifier can be shortened, and the input current during the period when the absolute value of the voltage of the AC power supply is low can be reduced. Can be appropriately set to reduce input current harmonics.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) As shown in FIG. 1, a power supply device of this embodiment includes a rectifier DB composed of a diode bridge for full-wave rectification of an AC power supply AC such as a commercial power supply. A capacitor C2 having a relatively small capacity is connected via a diode 11 between the DC output terminals of DB. One end of a capacitor C0 having a relatively large capacity is connected to a connection point between the rectifier DB and the diode D11. Capacitor C0, diode D11, capacitor C
2, a series circuit of a pair of switching elements Q1 and Q2 is connected in parallel, and a transformer T1 as a leakage transformer is provided between a connection point of the capacitor C2 and the diode D11 and a connection point of the switching elements Q1 and Q2. Is inserted. The load circuit 1 is connected to the secondary winding of the transformer T1.

Here, the load circuit 1 includes a discharge lamp (fluorescent lamp) FL in which one end of a filament is connected to both ends of a secondary winding of a transformer T1 and a non-power supply side end of each filament of the discharge lamp FL. And a capacitor C1 for preheating or resonance connected to the capacitor T1, and a resonance circuit is formed by the leakage inductance of the transformer T1 and the capacitor C1. The switching elements Q1 and Q2 use MOSFETs. The switching elements Q1 and Q2 are alternately turned on and off at a switching frequency sufficiently higher than the power supply frequency by a control circuit (not shown). By the way, in the conventional configuration of FIG. 15, an example is shown in which bipolar transistors are used as the switching elements Q1 and Q2. However, if MOSFETs are used as the switching elements Q1 and Q2 as in the present embodiment, a parasitic diode is formed in the MOSFET. because there is,
The diodes D1 and D2 become unnecessary.

Considering the operation in the steady state, since the capacitor C0 is charged in the steady state, when the switching element Q1 is turned on, the rectifier DB → the capacitor C0 → the switching as shown by the broken line in FIG. Element Q1 → primary winding of transformer T1 → capacitor C
2 → Current flows through the path of the rectifier DB, and power is supplied to the load circuit 1 via the transformer T1 while drawing in the input current. Next, when the switching element Q1 is turned off, the energy stored in the transformer T1 is changed from the primary winding of the transformer T1 to the capacitor C2 as shown by the broken line in FIG.
→ Parasitic diode of switching element Q2 → Transformer T
The energy of the transformer T1 is discharged to the path of the primary winding 1 and transferred to the capacitor C2. During these periods, the voltage V _C2 across the capacitor C2 increases due to the resonance action with the leakage inductance of the transformer T1 (FIG. 7 (c)).
reference).

Thereafter, when the switching element Q2 is turned on, the resonance action of the leakage inductance of the transformer T1 and the capacitors C1 and C2 causes the capacitor C2 → the primary winding of the transformer T1 → the switching element as shown by the broken line in FIG. A resonance current flows through the path from Q2 to capacitor C2, and power is supplied to the load circuit 1 via the transformer T1. At this time, since the direction of the current flowing through the primary winding of the transformer T1 is opposite to the direction when the switching element Q1 is on, an alternating high-frequency voltage can be applied to the load circuit 1.

When the electric charge of the capacitor C2 is released in the state of FIG. 4 and the voltage V _C2 across the capacitor C2 decreases to the output voltage of the rectifier DB as shown in FIG. 7C, as shown by a broken line in FIG. Rectifier DB → diode D11 → primary winding of transformer T1 → switching element Q2 → rectifier D
A current flows through the path B. That is, the input current Iin flows from the AC power supply AC to the rectifier DB.

Thereafter, when the switching element Q2 is turned off, as shown in FIG. 6, the energy stored in the transformer T1 is transferred to the primary winding of the transformer T1, the parasitic diode of the switching element Q1, the capacitor C0, and the diode D11. → Emitted through the path of the primary winding of the transformer T1. In this power supply device, since energy is stored in the transformer T1 not only from the capacitor C2 but also from the AC power supply AC, a relatively large amount of energy can be stored in the transformer T1. Further, all the charged charges of the capacitor C0 are given by the energy stored in the transformer T1.
By such an operation, the negative electrode of the capacitor C0 provided for smoothing corresponds to the positive electrode of the DC output terminal of the rectifier DB. Here, paying attention to the operations of FIGS. 5 and 6, the switching element Q2, the transformer T1, and the parasitic diode of the switching element Q1 are of a polarity reversal type (Buck Boos
This constitutes a (t-type) chopper circuit.

When the energy stored in the transformer T1 is released in the state shown in FIG. 6, the operation returns to the state in which the electric charge is released from the capacitor C0 as shown in FIG. 2, and the operations in FIGS. To supply the alternating high-frequency power to the load circuit 1.

FIG. 7 shows operation waveforms of each part in each state shown in FIGS. FIG. 3A shows a signal voltage input to the gate of the switching element Q1, and 0V corresponds to the off state of the switching element Q1. FIG.
Is the current I _T1 flowing in the primary winding of the transformer T1, and FIG. 3C is the power supply voltage Vs of the AC power supply AC and the capacitor C2.
The relationship between the voltage across V _C2 of FIG. (D) of indicating the input current Iin from the AC power source AC. A to e show states corresponding to FIGS. 2 to 6. As is clear from FIG. 7, there is a period during which the input current Iin flows from the AC power supply AC while the switching elements Q1 and Q2 are repeatedly turned on and off once. The switching frequency of switching elements Q1 and Q2 is set to such an extent that power supply voltage Vs of AC power supply AC can be regarded as constant during one cycle.

By such an operation, the operation waveform of each part of the circuit of FIG. 1 becomes as shown in FIG. 8 during one cycle of the voltage change of the AC power supply AC. 2A shows the waveform of the voltage V _C2 across the capacitor C2, FIG. 2B shows the current I _T1 flowing through the primary winding of the transformer _T1 , and FIG. 2C shows the input current Iin to the rectifier DB. (D) is a discharge lamp FL provided in the load circuit 1
Is the current I _La flowing through.

Here, in the present embodiment, similarly to the conventional configuration,
During the periods a and b shown in FIG. 7, the voltage V _C2 across the capacitor C2 increases due to the resonance operation (see FIG. 7C). However, in the present embodiment, since the diode D11 is inserted between the capacitor C2 and the capacitor C0, the voltage applied to the switching element Q1 during the OFF period of the switching element Q1 is different from the power supply voltage Vs of the AC power supply AC. The sum of the voltage across the capacitor C0 and the voltage across the capacitor C2 and the sum of the voltage V _C2 across the capacitor C2 and the voltage across the capacitor C0 are not applied to the switching element Q1 (that is, the voltage applied to the switching element Q1 is It does not depend on the voltage of the capacitor C2), so that the withstand voltage of the switching element Q1 can be reduced.

In the circuit configuration of the present embodiment, the rectifier DB → the capacitor 0 → the switching element Q1 → while the switching element Q1 is on as shown by the broken line in FIG.
Primary winding of transformer T1, capacitor C2, rectifier DB
Since the current flows through the path, the power supply voltage V of the AC power supply AC
The voltage V _C2 across the capacitor C2 during the period when the absolute value of s is low is reduced as shown in FIG. Therefore, the peak value of the primary voltage of the transformer T1 can be made substantially constant over one cycle of the AC power supply AC, and the crest factor of the current flowing through the load circuit 1 can be reduced.

Further, in the circuit configuration of the present embodiment, while the switching element Q2 is on, as shown by the broken line in FIG. 5, the rectifier DB → the diode D11 → the primary winding of the transformer T1 → the switching element Q2 → the rectifier. Current flows through the path of DB. Therefore, switching elements Q1, Q
2 repeats on / off once, there are two periods during which the input current Iin flows from the AC power supply AC. In other words, the input current Iin flows through two types of paths during the ON periods of the switching elements Q1 and Q2. Therefore, by appropriately setting the capacitance of the capacitor C2, it is possible to adjust the input current through the two types of paths, reduce input current harmonics, and increase the input power factor. In addition, the above object can be achieved with a relatively small number of components because only the diode D11 is added to the components of the conventional configuration shown in FIG.

Although not shown in FIG. 1, a high frequency blocking filter circuit may be inserted between the AC power supply AC and the rectifier DB in order to prevent high frequency components from being mixed into the AC power supply AC. Not to mention the good things.

(Second Embodiment) In the first embodiment, the configuration including the transformer T1 which is a leakage transformer as the load circuit 1 has been described. However, as shown in FIG.
The same operation is performed by employing a configuration in which the inductor L1 is connected to the secondary winding of the transformer T2 in series while using the inductor 2 in series. That is, the inductor L1 is used instead of the leakage inductance of the transformer T1. Other configurations and operations are the same as those of the first embodiment. In each of the embodiments described later, the transformer T2 is used instead of the transformer T1.
And the inductor L1.

(Embodiment 3) In this embodiment, as shown in FIG. 10, the positive electrode of the capacitor C0 provided for smoothing in the first embodiment corresponds to the negative electrode of the DC output terminal of the rectifier DB. . In short, in the circuit configuration of FIG. 1, the positive and negative electrodes of the DC output terminal of the rectifier DB are replaced. Note that a leakage transformer is used for the transformer T1 as in the first embodiment, and the load circuit 1 includes a discharge lamp FL similar to the first embodiment.

Also in this configuration, as in the first embodiment, since the diode D11 is inserted between the capacitor C2 and the capacitor C0, the capacitor C2
Is applied to the diode D11,
The voltage applied to the switching element Q1 can be reduced, and the withstand voltage of the switching element Q1 can be reduced. Further, since the voltage V _C2 across the capacitor C2 is reduced during the period when the absolute value of the power supply voltage Vs of the AC power supply AC is low, the peak value of the primary voltage of the transformer T1 is made substantially constant over one cycle of the AC power supply AC. It is possible to reduce the crest factor of the current flowing through the load circuit 1.

(Embodiment 4) In the present embodiment, as shown in FIG.
And a capacitor C3 connected in parallel.

In this configuration, during the period a shown in FIG. 7, the primary winding of the transformer T1 → the capacitor C3 → the capacitor C0 → the switching element Q1 → the primary winding of the transformer T1, as shown by the broken line in FIG. , The period for charging the capacitor C3 is provided, so that the rectifier D
B → Capacitor C0 → Switching Element Q1 → Primary Winding of Transformer T1 → Capacitor C2 → Rectifier DB The input current Iin is shortened during the period of drawing the input current Iin, and the input current Iin during the period when the absolute value of the voltage of the AC power supply AC is low. Is reduced. Therefore, by appropriately setting the capacitances of the capacitors C2 and C3, the input current Iin through the above two types of paths can be adjusted, the input current harmonics can be reduced, and the input power factor can be increased.

In this embodiment, as in the first embodiment, the withstand voltage of the switching element Q1 can be made lower than in the conventional configuration, and the crest factor of the current output to the load circuit 1 can be further reduced.

(Embodiment 5) As shown in FIG. 13, the present embodiment has the same configuration as that of Embodiment 1 shown in FIG. 1, but is for controlling on / off of the switching elements Q1 and Q2. The control circuit 3 is shown. The difference between the present embodiment and the first embodiment is that the control circuit 3 is capable of arbitrarily controlling a switching frequency for turning on and off the switching elements Q1 and Q2, an on-time, a duty ratio, and the like. The point is that the supplied power can be adjusted. That is, the light output of the discharge lamp FL can be adjusted, and dimming control can be performed. Here, the above-described control of the on-time means that the on-time is changed (generally, the off-time is kept constant), and the control of the duty ratio means that the ratio between the on-time and the off-time is made constant with the frequency kept constant. Means to change.

For example, if the ratio of the ON period to one cycle of the switching element Q2 is controlled to be small,
AC power supply A when switching element Q2 is on
The power taken from C is reduced, and abnormal voltage rise of the voltage between both ends of the capacitor C0 due to excess energy can be prevented. For example, in the load circuit 1 including the discharge lamp FL, it is necessary to preheat or start the discharge lamp FL, and during these periods, the power consumption of the load circuit 1 is small. By shortening the period, it is possible to prevent abnormal voltage increase of the voltage across the capacitor C0.

As the control circuit 3, as in this embodiment,
By using an element that can control at least one of a switching frequency and a duty ratio for turning on and off the switching elements Q1 and Q2, the discharge lamp FL
When the lamp is turned on, the power supplied to the load circuit 1 can be changed by changing at least one of the on / off switching frequency and the duty ratio of the switching elements Q1 and Q2, and the dimming of the discharge lamp FL becomes possible. . Further, even when dimming is performed, the switching element Q
By adjusting the ON time of No. 2, it is possible to suppress an increase in the voltage across the capacitor C0 and prevent an abnormal boost.

In the configuration of the present embodiment, the control circuit 3 enables control of preheating, starting and lighting of the discharge lamp FL provided in the load circuit 1 and discharge by adjusting the power supplied to the load circuit 1. It is also possible to dimming the light output of the lamp FL. Further, it is possible to prevent abnormal voltage increase of the voltage between both ends of the capacitor C0 due to the fluctuation of the power consumption in the load circuit 1, thereby preventing the destruction of the circuit components. Other configurations and operations are the same as those of the first embodiment.

(Embodiment 6) The circuit configuration of this embodiment is the same as that of Embodiment 5, and the power supply method to the load circuit 1 is different.

In this embodiment, for example, the discharge lamp FL
In order to reduce the power consumption by the control circuit 3, the control circuit 3 increases the operating frequency of the switching elements Q1 and Q2,
It is characterized in that the ratio of the ON period of the switching element Q2 to one cycle of the switching element Q2 is reduced.
Thus, in the present embodiment, the power taken from the AC power supply AC when the switching element Q2 is on is reduced, and abnormal boosting of the capacitor C0 due to surplus power can be prevented, thereby preventing the destruction of the circuit components. be able to. Also, in the present embodiment, similarly to the fifth embodiment, the light output of the discharge lamp FL can be adjusted.

(Embodiment 7) In this embodiment, as shown in FIG. 14, a control circuit 3 similar to that of Embodiment 5 is provided in the configuration of Embodiment 3, and furthermore, a voltage detection circuit for detecting a voltage across the capacitor C0. A circuit 4 is added, and the control circuit 3 switches the switching element Q based on the voltage detected by the voltage detection circuit 4.
1, Q2 ON / OFF switching frequency, ON time,
The duty ratio is changed, and the on / off of the switching elements Q1 and Q2 is stopped as necessary.

That is, if the voltage across the capacitor C0 is controlled to be substantially constant, the voltage applied to the load circuit 1 can be stabilized, and stable operation of the load circuit 1 can be expected. Therefore, the voltage applied to the discharge lamp FL can be stabilized, and the output fluctuation of the discharge lamp FL can be suppressed. Further, when the voltage across the capacitor C0 rises and reaches a predetermined value, the switching elements Q1 and Q2 are stopped from being turned on and off, or the switching frequency is made sufficiently high to cause destruction due to application of an overvoltage to circuit components. Can be avoided.

The second to seventh embodiments described above
In the same manner as in the first embodiment, a high frequency blocking filter circuit may be inserted between the AC power supply AC and the rectifier DB in order to prevent high frequency components from being mixed into the AC power supply AC. Absent.

[0049]

According to the first aspect of the present invention, there is provided a rectifier for rectifying an AC power supply, a first series circuit of a first diode and a first capacitor connected between the DC output terminals of the rectifier, A second capacitor having one end connected to a connection point with the first diode and having a capacity sufficiently larger than the capacity of the first capacitor; and a second capacitor connected between both ends of the first series circuit via the second capacitor. A second series circuit of the first and second switching elements, which is alternately turned on and off at a frequency sufficiently higher than the frequency of the AC power supply; Second and third diodes for conducting current;
A primary winding is inserted between a connection point between the diode and the first capacitor and a connection point between the first and second switching elements to provide a secondary output to a load circuit; Since the first diode is inserted between the first capacitor and the second capacitor,
During the off period of the first switching element, the sum of the voltage across the first capacitor and the voltage across the second capacitor is equal to the first voltage.
Is not applied to the first switching element.
This has the effect that the breakdown voltage of the switching element can be reduced. In addition, during the period when the first switching element is on, current flows through the path of the rectifier, the second capacitor, the first switching element, the primary winding of the transformer, the first capacitor, and the rectifier. The voltage of the first capacitor during a period in which the absolute value of the voltage is low is reduced,
The crest value of the primary voltage of the transformer can be made substantially constant over one cycle of the AC power supply, and the crest factor of the current flowing through the load circuit can be reduced. In addition, while the second switching element is on, current flows through the rectifier, the first diode, the primary winding of the transformer, the second switching element, and the rectifier.
The input current flows in different paths during the ON periods of the first switching element and the second switching element, and the input current harmonics can be reduced by appropriately setting the capacity of the first capacitor. There is an effect that there is. Moreover, since the number of parts is only the addition of the first diode, the above object can be achieved with a relatively small number of parts.

According to a second aspect of the present invention, in the first aspect of the present invention, a control circuit capable of adjusting the on / off switching frequency of the first and second switching elements is provided.
There is an effect that the power supply to the load circuit can be adjusted by changing the switching frequency.

According to a third aspect of the present invention, in the first or second aspect of the present invention, since a control circuit capable of adjusting the on-period of the first and second switching elements is provided, the on-period of the switching element is changed. This has the effect that the power supplied to the load circuit can be adjusted.

According to a fourth aspect of the present invention, in the third aspect of the present invention, when the control circuit reduces the power consumption of the load circuit, the control circuit performs the second switching with respect to the sum of the ON period and the OFF period of the second switching element. Since the ratio of the ON period of the element is reduced, it is possible to adjust the power supplied to the load circuit and the input current, and it is possible to suppress an abnormal increase in the voltage across the second capacitor.

According to a fifth aspect of the present invention, in the first aspect of the present invention, a voltage detecting means for detecting a voltage between both ends of the second capacitor is provided, and the first and the second switching are performed based on a voltage detected by the voltage detecting means. A control circuit for controlling at least one of a switching frequency for turning on / off the element and an on-period is provided. When the voltage across the second capacitor rises abnormally, the operation is stopped or the load circuit By reducing the output of the above, there is an effect that stress can be prevented from being applied to the circuit components. Further, if the voltage across the second capacitor is controlled to be kept substantially constant, the current supplied to the load circuit will be kept substantially constant, and stable operation of the load circuit can be expected. In particular, when the load circuit includes a discharge lamp, a light output with less flicker can be obtained.

According to a sixth aspect of the present invention, in the first aspect of the present invention, since a third capacitor connected in parallel to the first diode is provided, the first switching element is turned on during the period when the first switching element is on. Next winding, third capacitor, second
Capacitor, first switching element, transformer 1
A period for charging the third capacitor in the path of the secondary winding is provided, and the primary winding of the rectifier, the second capacitor, the first switching element, and the transformer is provided while the first switching element is on. , The period during which current flows through the path of the first capacitor and the rectifier can be shortened, and the input current during the period when the absolute value of the voltage of the AC power supply is low can be reduced. Has an effect that input current harmonics can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is an operation explanatory view of the above.

FIG. 3 is an operation explanatory view of the above.

FIG. 4 is an operation explanatory view of the above.

FIG. 5 is an operation explanatory view of the above.

FIG. 6 is an operation explanatory view of the above.

FIG. 7 is an operation explanatory diagram of the above.

FIG. 8 is an operation explanatory view of the above.

FIG. 9 is a circuit diagram showing a second embodiment of the present invention.

FIG. 10 is a circuit diagram showing a third embodiment of the present invention.

FIG. 11 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 12 is an operation explanatory view of the above.

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

FIG. 14 is a circuit diagram showing a seventh embodiment of the present invention.

FIG. 15 is a circuit diagram showing a conventional example.

FIG. 16 is an operation explanatory view of the above.

FIG. 17 is an operation explanatory view of the above.

FIG. 18 is an operation explanatory view of the above.

FIG. 19 is a diagram illustrating the operation of the above.

FIG. 20 is an explanatory diagram of the operation of the above.

FIG. 21 is an explanatory diagram of the operation of the above.

FIG. 22 is an explanatory diagram of the above operation.

FIG. 23 is an explanatory diagram of the operation of the above.

FIG. 24 is a circuit diagram of another conventional example.

[Explanation of symbols]

 1 Load circuit AC AC power supply T1 Transformer Q1, Q2 Switching element D11 Diode C0 Capacitor C1 Capacitor C2 Capacitor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K072 AA02 BA03 BB01 BC01 BC02 CA14 DB03 DD04 EB05 GA03 GB12 GC04 HA06 HA10 HB03 5H007 AA02 AA08 BB03 CA02 CB04 CB17 CB22 CB25 CC03 CC12 CC32 DA05 DA06 DC05

Claims (6)

[Claims] 1. A rectifier for rectifying an AC power supply, a first series circuit including a first diode and a first capacitor connected between DC output terminals of the rectifier, and a connection between the rectifier and the first diode. A second capacitor having one end connected to the point and having a capacity sufficiently larger than the capacity of the first capacitor;
Of the first and second switching elements, which are connected between both ends of the first series circuit through the capacitors of the first and second switching elements and are alternately turned on and off at a frequency sufficiently higher than the frequency of the AC power supply.
, A second diode and a third diode connected in parallel to the respective switching elements, and flowing currents in the opposite directions to those when the respective switching elements are turned on, the first diode and the first diode.
And a transformer having a primary winding inserted between the connection point of the capacitor and the connection point of the first and second switching elements to provide a secondary output to a load circuit. 2. The power supply device according to claim 1, further comprising a control circuit capable of adjusting an on / off switching frequency of the first and second switching elements. 3. The power supply device according to claim 1, further comprising a control circuit capable of adjusting an on-period of the first and second switching elements. 4. The control circuit according to claim 1, wherein when reducing the power consumption of the load circuit, a ratio of an ON period of the second switching element to a sum of an ON period and an OFF period of the second switching element is reduced. The power supply device according to claim 3, wherein 5. A voltage detecting means for detecting a voltage between both ends of the second capacitor, wherein at least a switching frequency for turning on and off the first and second switching elements and an on-period based on a voltage detected by the voltage detecting means. 2. The power supply device according to claim 1, further comprising a control circuit for controlling one of the power supplies. 6. A third diode connected in parallel to the first diode.
The power supply device according to claim 1, further comprising: