JP3494035B2 - Power supply - Google Patents

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 supplying high frequency power to a load circuit by converting the power of an alternating current power supply to direct current and then converting the power of direct current to high frequency.

[0002]

2. Description of the Related Art As a power supply device of this type, there is a circuit as shown in FIG. This circuit is provided between the DC output terminals of a rectifier DB for full-wave rectifying an AC power source Vs such as a commercial power source.
A series circuit including a smoothing capacitor C1, a diode D2, and a primary winding of the leakage transformer T1 is connected, and by operating an inverter circuit INV that uses the smoothing capacitor C1 as a power source, high-frequency power is supplied to a discharge lamp La as a load. It is configured to supply and charge the smoothing capacitor C1.

The inverter circuit INV has a pair of switching elements Q connected across the smoothing capacitor C1.
1 and Q2 are provided in series, and both switching elements Q1,
The drive circuit DV alternately turns on and off Q2 at a frequency sufficiently higher than the power supply frequency of the AC power supply AC. In the illustrated example, bipolar transistors are used as the switching elements Q1 and Q2.
Diodes D1 and D2 are respectively connected in antiparallel to the switching elements Q1 and Q2 in order to form a path for current regeneration when the transistor 2 is turned off. That is, the diode D
1, 1 and 2 are connected in parallel to the switching elements Q1 and Q2, respectively, so that a current in a direction opposite to that when the switching elements Q1 and Q2 are turned on can pass. When MOSFETs or the like are used as the switching elements Q1 and Q2, the body diodes function as the diodes D1 and D2, so that the diodes D1 and D2 can be omitted.

A small capacity (smoothing capacitor) as an impedance element is provided between the connection point of both switching elements Q1 and Q2 (the output terminal of the inverter circuit INV) and one DC output terminal (the positive electrode in the illustrated example) of the rectifier DB. A series circuit of a capacitor C2 having a capacity sufficiently smaller than that of C1) and a primary winding of the leakage transformer T1 is connected. The connection point between the capacitor C2 and the primary winding of the leakage transformer T1 is connected to the other DC output terminal (negative electrode in the illustrated example) of the rectifier DB. Therefore, the capacitor C2
Will be connected between the DC outputs of the rectifier DB.

A discharge lamp La having a filament such as a fluorescent lamp between both ends of the secondary winding of the leakage transformer T1.
And a capacitor C3 that forms a resonance circuit together with the leakage inductance of the leakage transformer T1 is connected between the non-power source side ends of both filaments of the discharge lamp La. The capacitor C3 forms a path through which a preheating current flows when the filament of the discharge lamp La is preheated.

The normal operation of the circuit shown in FIG. 11 will be briefly described. When the switching element Q2 is on, a current flows through the path of the smoothing capacitor C1-capacitor C2-leakage transformer T1-switching element Q2-smoothing capacitor C1. At this time, the voltage across the capacitor C2 increases due to the resonance action of the resonance circuit composed of the capacitor C2 and the leakage inductance of the leakage transformer T1. The resonance frequency of this resonance circuit is set lower than the switching frequencies of the switching elements Q1 and Q2, the direction of the current does not reverse during the ON period of the switching element Q2, and the leakage transformer remains even after the switching element Q2 is turned OFF. The current continues to flow in the path of T1-diode D1-capacitor C2-leakage transformer T1, and the energy accumulated in the leakage transformer T1 is released. That is, the voltage across the capacitor C2 continues to increase, and the diode D1 forms a path through which the regenerative current flows.

Next, when the switching element Q1 is turned on, the leakage inductance of the leakage transformer T1 and the resonance action of the capacitors C2 and C3 reverse the direction of the current flowing through the primary winding of the leakage transformer T1,
A current flows through the path of the capacitor C2-the switching element Q1-the leakage transformer T1-the capacitor C2. In this way, when the capacitor C2 is discharged and the voltage across the capacitor C2 becomes lower than the output voltage of the rectifier DB, the rectifier DB-the switching element Q1-the leakage transformer T1.
-A current will flow in the path of the rectifier DB. That is, the input current flows from the AC power supply Vs to the rectifier DB.
Since the current continues to flow in the same direction in the primary winding of the leakage transformer T1 even if the switching element Q1 is turned off, the current flows through the path of the rectifier DB-smoothing capacitor C1-diode D2-leakage transformer T1-rectifier DB. Flows, and the rectifier DB from the AC power supply Vs
Input current flows to. Thus, when the added voltage of the output voltage of the rectifier DB and the voltage across the primary winding of the leakage transformer T1 becomes lower than the voltage across the smoothing capacitor C1, the diode D2 becomes non-conductive, and the input current from the AC power supply Vs becomes Stop. After that, the switching element Q2
Is turned on again, and the above operation is repeated.

As is clear from the above description, during one cycle of the on / off operation of the switching elements Q1 and Q2 in the inverter circuit INV, the rectifier D is switched from the AC power source Vs.
Since there is a period in which the input current flows in B, and the switching frequency of the switching elements Q1 and Q2 is sufficiently higher than the power supply frequency of the AC power supply Vs, almost the entire period within one cycle of the voltage waveform of the AC power supply Vs. , The input current from the AC power supply Vs to the rectifier DB can be passed at high frequency,
The envelope of the input current waveform to the rectifier DB can be made to continue almost smoothly. As a result, AC power supply V
If a filter that blocks a high frequency of about the switching frequency is provided between s and the rectifier DB, the input current from the AC power supply Vs can be made substantially continuous, and an increase in harmonic distortion of the input current can be suppressed. it can. Further, the input current waveform becomes substantially similar to the voltage waveform of the AC power supply Vs, and it is possible to suppress the decrease of the input power factor. That is, a power supply device with low input distortion and high power factor can be provided.

By the way, as described above, the switching frequency of the inverter circuit INV is set higher than the resonance frequency of the resonance circuit, and the load current is in a lag phase. However, for example, when a phase advance current flows in the load. The operation becomes abnormal and stress is applied to the components such as the switching elements Q1 and Q2. Therefore, in order to detect such an operation abnormality, as shown in FIG. 12, a detection resistor Rsc is connected in series to the switching element Q2 (in the illustrated example, the emitter of the switching element Q2 and the smoothing capacitor C2).
(Connected to the negative electrode of 1), a voltage obtained by half-wave rectifying the voltage across the detection resistor Rsc with a diode Df,
It is considered to compare with the reference voltage Vk by the comparator CP1. In the illustrated example, the reference voltage Vk is applied to the inverting input terminal of the comparator CP1, and the output of the comparator CP1 is connected to the H level when the voltage across the detection resistor Rsc exceeds the reference voltage Vk.

Therefore, if the drive circuit DV is configured so that the output of the comparator CP1 becomes H level when the output of the comparator CP1 becomes H level, the inverter circuit INV is provided when an abnormality such as a leading current flows. The operation of can be stopped. Further, by configuring the drive circuit DV so that the switching frequency of the inverter circuit INV is increased when the output of the comparator CP1 becomes H level, it is possible to cope with the abnormality such as the advance current flows. As described above, when the peak value of the current passing through the detection resistor Rsc becomes larger than the reference voltage Vk, it is determined that an abnormality has occurred, and the drive circuit DV is controlled to reduce the stress on the components. Of.

By the way, it is considered that the reference voltage Vk is a constant voltage and the reference voltage Vk is changed according to the operating state of the discharge lamp La (for example, the dimming amount).

FIG. 13 shows the relationship with the reference voltage Vk when the voltage across the detection resistor Rsc changes when the reference voltage Vk is kept constant. FIG.
(A) is a state in which the discharge lamp La is lit at almost the rated value,
FIG. 13C shows the discharge lamp L with the light output reduced to near the lower limit value.
FIG. 13B shows a state in which the discharge lamp La is dimmed and lit so that a light output about the middle of the two is obtained. In the figure, the voltage Vk1 indicates the voltage value of the reference voltage Vk, and the waveform changing up and down indicates the voltage across the detection resistor Rsc. In addition,
When the discharge lamp La is dimmed and lit, the switching frequency of the inverter circuit INV may be changed in the lighting state of the discharge lamp La, or the ratio (duty ratio) of the ON periods of both switching elements Q1 and Q2 may be changed. ,
The light output can be changed.

Each of the states shown in FIGS. 13 (a) to 13 (c) indicates a normal operation state, and in each case, the voltage across the detection resistor Rsc is set to be lower than the reference voltage Vk1. Since the reference voltage Vk1 must be set, the reference voltage Vk is higher than the peak voltage in the state of FIG. 13A in which the amplitude of the voltage across the detection resistor Rsc is the largest.
The reference voltage Vk1 is set so that k1 becomes high. With this setting, the output of the comparator CP1 is maintained at the L level during normal operation, and the inverter circuit INV continues its operation.

On the other hand, when an abnormality such as a leading current flows, the voltage across the detection resistor Rsc abnormally rises, and the peak value of the voltage across the detection resistor Rsc exceeds the reference voltage Vk1. . As a result, the comparator C
A period in which the output of P1 becomes H level occurs, and the drive circuit DV
Controls the switching elements Q1 and Q2 so that the output of the inverter circuit INV becomes small, thereby suppressing an increase in stress on the components.

On the other hand, FIG. 14 shows the relationship between the reference voltage Vk and the reference voltage Vk when the voltage across the detection resistor Rsc changes when the reference voltage Vk is changed according to the state of the load. FIG. 14A shows a state in which the discharge lamp La is lit almost at a rating, and FIG. 14C shows a state in which the discharge lamp La is dimmed and lit by narrowing the light output to near the lower limit value. (B) shows a state in which the discharge lamp La is dimmed and lit so as to obtain a light output about the middle of the two. In the figure, voltages Vk1 to Vk3 indicate the voltage values of the reference voltage Vk, respectively.

Each of the states shown in FIGS. 14A to 14C shows a normal operation state, and each reference voltage V is higher than the peak value of the voltage across the detection resistor Rsc in each state.
The reference voltages Vk1 to Vk3 in each state are set so that k1 to Vk3 are slightly higher. Thus, the reference voltage V
Even if k1 to Vk3 are changed, the output of the comparator CP1 is maintained at the L level during normal operation, and the inverter circuit INV continues its operation.

When an abnormality such as a leading current flows, the voltage across the detection resistor Rsc abnormally rises, the peak value of the voltage across the detection resistor Rsc exceeds the reference voltage Vk1, and the comparator CP1 There is a period in which the output of H becomes H level. In such a state, the drive circuit DV controls the switching elements Q1 and Q2 so that the output of the inverter circuit INV becomes small, thereby suppressing an increase in stress on the components.

[0018]

As described above, the inverter circuit INV operates normally when the reference voltage Vk is constant or when the voltage is changed according to the operating state of the load. It is possible to continue and reduce the output of the inverter circuit INV at the time of abnormality.

However, if the reference voltage Vk is a constant voltage, as is apparent from FIG.
In the period in which the peak value of the voltage across both ends becomes small, the difference between the peak value and the reference voltage Vk becomes large, and even if an abnormality occurs, the peak value of the voltage across the detection resistor Rsc hardly exceeds the reference voltage Vk, The detection of abnormality may be delayed. In other words, even if an abnormality occurs in the state where the light is controlled near the lower limit, it is difficult to detect the abnormality, which causes a problem that stress is applied to the component parts.

On the other hand, if the reference voltage Vk is changed according to the operating state of the load, the difference between the peak value of the voltage across the detection resistor Rsc and the reference voltage Vk can always be kept small. Is not a problem.
However, in order to change the reference voltage Vk according to the operating state of the load, there is a problem that the circuit configuration becomes complicated and the number of parts increases as compared with the case where the reference voltage Vk is a constant voltage.

The present invention has been made in view of the above reasons, and an object thereof is to quickly detect an abnormality while setting a reference value to be compared with a detection value that changes depending on the presence or absence of an abnormality to a substantially constant value. It is possible to provide a power supply device that can prevent unnecessary stress from being applied to the components.

[0022]

According to a first aspect of the present invention, a rectifier for rectifying an AC power source, a transformer having a load connected to a secondary side thereof, and a series circuit of a primary winding of the transformer have a DC rectifier. A first switching element inserted between the output terminals,
A second switching element connected in series to the first switching element, a detection resistor connected in series with the first and second switching elements, and a series connection of the first and second switching elements and detection resistor A smoothing capacitor connected in parallel to the circuit, first and second diodes connected in parallel to the first and second switching elements and capable of passing a current in a direction opposite to that when each switching element is on, and an alternating current A drive circuit that alternately turns on and off the first and second switching elements at a frequency sufficiently higher than the power source frequency of the power source, and is connected between both ends of the series circuit of the primary winding of the transformer and the first switching element. A capacitor that forms a resonance circuit with the inductance component of the transformer and the load, and a resistance for detection during the ON period of the second switching element. And an abnormality detection circuit that controls the drive circuit in a direction to eliminate the abnormality by detecting the voltage across both ends of the voltage in the vicinity of the peak value of the voltage of the AC power supply and determining that the detected voltage exceeds the reference voltage. .
According to this configuration, in the abnormality detection circuit, the current in the ON period of the second switching element of the voltage across the detection resistor is detected only near the peak value of the voltage of the AC power supply, and as described below. , The peak value of the voltage across the detection resistor detected during this period is almost constant regardless of the power supplied to the load, so the reference voltage remains unchanged even if the switching frequency of the first and second switching elements is changed. The voltage can be set to a constant voltage close to the peak value of the voltage across the detection resistor, and as a result, the circuit configuration required to set the reference voltage is simple. Moreover, even if the switching frequency changes, the difference between the peak value of the voltage across the detection resistor and the reference voltage when the load is normal can be set to a relatively small value. It is possible to suppress stress on the components.

According to a second aspect of the present invention, in the first aspect of the present invention, the abnormality detection circuit detects a power supply voltage detection circuit for detecting a predetermined period near the peak value of the voltage of the AC power supply and a voltage across the detection resistor. A diode for half-wave rectifying and extracting the voltage across the detection resistor generated by the current flowing through the detection resistor during the ON period of the second switching element, and a detection for detecting by the power supply voltage detection circuit and extracted by the diode during the predetermined period. It consists of a multiplier that allows the voltage across the resistor to pass, and a comparator that compares the output of the multiplier with a reference voltage. According to this configuration, by using the multiplier, the voltage across the detection resistor can be input to the comparator and compared with the reference voltage only during a predetermined period near the peak value of the voltage of the AC power supply. The abnormality detection circuit of the invention can be easily realized by this configuration.

According to a third aspect of the present invention, in the second aspect of the present invention, the power supply voltage detection circuit detects a period during which the output voltage of the rectifier is equal to or higher than a set voltage. According to this configuration, the output voltage of the rectifier is used to detect the predetermined period near the peak value of the voltage of the AC power supply,
It is not necessary to separately provide a rectifier, and the circuit configuration is relatively simple.

According to a fourth aspect of the present invention, in the second or third aspect of the invention, a filter circuit for removing a high frequency component from the voltage across the detection resistor is provided. According to this configuration, high-frequency noise is removed from the voltage across the detection resistor, so that malfunction due to noise can be reduced.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) Since the basic configuration of this embodiment is the same as the conventional configuration shown in FIG. 12, the components having the same functions are designated by the same reference numerals. The description will be omitted, and the characteristic part of the present embodiment will be mainly described below.

In this embodiment, the voltage across the detection resistor Rsc is half-wave rectified by the diode Df and is not directly input to the comparator CP1 but is input to the multiplier M1 and the multiplier M1 detects the power supply voltage. Circuit V
The result of multiplication with the output of D is input to the comparator CP1. The power supply voltage detection circuit VD is a circuit that outputs a predetermined value during a period when the absolute value of the voltage of the AC power supply Vs is equal to or higher than a preset specified voltage, and outputs 0 V during a period when the absolute value is less than the specified voltage. Power supply voltage detection circuit VD and diode D
An abnormality detection circuit is configured by f, the multiplier M1, and the comparator CP1.

In this configuration, a voltage corresponding to a voltage obtained by half-wave rectifying the voltage across the detection resistor Rsc is input to the comparator CP1 while the absolute value of the voltage of the AC power supply Vs is near the peak value. The input to the comparator CP1 becomes 0 during the period near the zero cross point of the voltage waveform. Even if the state of the discharge lamp La changes, the change in the peak value of the voltage across the detection resistor Rsc is small in the vicinity of the peak value of the voltage of the AC power supply Vs. As a result, even if the reference voltage Vk is constant, The difference from the peak value of the voltage between both ends can always be made small regardless of the load condition. Here, since the output of the power supply voltage detection circuit VD is binary, the multipliers input to the multiplier M1 may be 0 and 1, and it is possible to use, for example, an analog switch as the multiplier M1.

The reason why the peak value of the voltage across the detection resistor Rsc becomes almost constant regardless of the load condition near the peak value of the voltage of the AC power supply Vs will be considered below.

FIG. 2A shows the voltage waveform of the AC power supply Vs. At this time, the output of the power supply voltage detection circuit VD is shown in FIG.
become that way. The voltage across the detection resistor Rsc is
It changes like FIG.2 (b)-(d) according to the state of a load. FIG. 2B shows a state in which the discharge lamp La is substantially turned on, and FIG. 2C shows a state in which dimming is turned on and when the light output at the time of rated lighting is 100%. FIG. 2D shows a state in which the light output is narrowed down to about 50%, and a state in which the light output is turned on, and the light output is narrowed down to an adjustable lower limit value. The voltage across the detection resistor Rsc changes at a high frequency as shown by the broken line that changes finely in FIGS. 2B to 2D, and the envelope of the change in the voltage across the detection resistor Rsc is AC. The voltage waveform of the power supply Vs changes so as to have a half cycle period.

When dimming is performed by changing the switching frequency of the inverter circuit INV or changing the duty ratio of the switching elements Q1 and Q2, the voltage across the detection resistor Rsc is as described above. The waveforms of the currents that change as shown in (b) to (d) and naturally flow through the switching element Q2 are shown in FIGS.
It becomes similar to the waveform shown in (d).

By the way, when the voltage across the detection resistor Rsc is enlarged near the peak value (point A in FIG. 2) and near the zero cross point (point B in FIG. 2) of the voltage waveform of the AC power source Vs, respectively, It becomes like FIG. 3 and FIG. 3 and 4
And (a) to (c) are shown in FIG.
The state corresponding to (d) is shown. As is apparent from FIG. 4, the peak value of the voltage across the detection resistor Rsc changes depending on the dimming amount near the zero cross point of the voltage waveform of the AC power supply Vs, and the deeper the dimming, the smaller the peak value. On the other hand, as is apparent from FIG. 3, when the dimming amount changes near the peak value of the voltage of the AC power supply Vs, the lower limit value of the voltage across the detection resistor Rsc changes, but the peak value ( The upper limit) is almost constant.

The voltage across the detection resistor Rsc has the above-mentioned waveform in the circuit configuration shown in FIG.
Not only the leakage transformer T1 constitutes a resonance circuit together with the capacitor C2, but also the leakage transformer T1
It is considered that the primary winding of the above constitutes a kind of chopper circuit together with the switching element Q1 and the diode D2. That is, the energy accumulated in the leakage transformer T1 during the ON period of the switching element Q1 is released after the OFF of the switching element Q1, and the input current flows from the AC power supply Vs to the rectifier DB during the energy releasing period.
At the same time, the smoothing capacitor C1 is charged. The current relating to the operation of the chopper circuit as described above is extracted from the current iT1 flowing through the primary winding of the leakage transformer T1 as shown in FIG. That is, the envelope of the current iT1 is almost proportional to the absolute value of the voltage of the AC power supply Vs.

As described above, the voltage across the detection resistor Rsc is obtained by superposing the current related to the operation of the chopper circuit as described above and the current related to the operation of the inverter circuit INV by the power supply from the smoothing capacitor C1. Considered to be electric current. Therefore, when the output voltage waveform of the rectifier DB is near the peak value, both currents are almost canceled out and the detection resistor R is turned on during the ON period of the switching element Q2.
The peak value of the current flowing through sc becomes small. Further, during the period near the zero cross point of the voltage waveform of the AC power supply Vs,
While the current related to the operation of the chopper circuit becomes small, the current related to the operation of the inverter circuit INV is kept almost constant by the power supply from the smoothing capacitor C1, and therefore, the current for the switching element Q2 is for detection. It is considered that the peak value of the current flowing through the resistor Rsc becomes relatively large. Then, since the current related to the operation of the inverter circuit INV changes according to the consumption current (that is, the depth of dimming) in the discharge lamp La, the detection resistor Rsc is eventually obtained.
The positive peak value of the voltage across both ends of the output voltage waveform of the rectifier DB changes in accordance with the dimming depth of the discharge lamp La in the period near the zero cross point of the voltage waveform of the AC power supply Vs. During the certain period, even if the dimming depth of the discharge lamp La changes, it hardly changes. Therefore, if the voltage across the detection resistor Rsc is taken out only during the period when the output voltage of the rectifier DB is close to the peak value and the current flows through the switching element Q2, there is almost no effect on the dimming depth. The voltage that is not applied can be taken out.

As is clear from the above description, if the reference voltage Vk of the comparator CP1 for detecting an abnormality due to the influence of the phase advancing operation is set for the voltage waveform shown in FIG. Even if the reference voltage Vk is not changed according to the dimming depth and is set to a substantially constant value, the detection resistor R
The difference between the peak value of the voltage across sc and the reference voltage Vk can be set small regardless of the dimming depth of the discharge lamp La, and surge current due to an abnormality such as a phase advance operation can be detected quickly. It will be possible. Moreover, the voltage waveform of FIG. 3 is a waveform resulting from the superimposition of the current relating to the operation of the chopper circuit as described above, and is a waveform which is more likely to be affected by the phase-advancing operation than the voltage waveform of FIG. I can say. In other words, during the period when the output voltage of the rectifier DB is near the peak value, the effect of the phase advance operation is more likely to occur than during the period when the voltage waveform of the AC power supply Vs is near the zero cross point. It becomes possible to detect.

As described above, by setting the reference voltage Vk of the comparator CP1 to a constant value, the reference voltage Vk
Is simpler than in the case of changing according to the dimming depth of the discharge lamp La, and moreover, the voltage across the detection resistor Rsc is taken out only during the period when the voltage waveform of the AC power supply Vs is near the peak value. Thus, it is possible to quickly detect an abnormality such as a phase advance operation.

FIG. 6 specifically shows a circuit for generating the power supply voltage detection circuit VD and the reference voltage Vk. The power supply voltage detection circuit VD performs full-wave rectification using the rectifier DB2 formed of a diode bridge after stepping down the voltage of the AC power supply Vs by the transformer T2, and a resistor R3 and a capacitor C5 connected between the DC output terminals of the rectifier DB2.
The comparator CP2 compares the voltage smoothed by the smoothing circuit of No. 2 with the reference voltage obtained by dividing the control power supply voltage (constant voltage) Vcc by the series circuit of the resistors R1 and R2.
Therefore, if the reference voltage is set appropriately, the AC power source V
The output of the comparator CP2 can be set to the H level during a desired period when the voltage of s is near the peak value. Further, the reference voltage Vk is obtained by dividing the control power supply voltage Vcc by the resistors R4 and R5.

With the above configuration, the inverter circuit INV is normally operated while the output of the comparator CP1 is at the L level, and when the output of the comparator CP1 is at the H level, the drive circuit DV keeps the switching elements Q and Q2 off. Or the frequency at which the switching elements Q1 and Q2 are turned on / off can be increased so that the delay operation can be surely performed.

Although only one discharge lamp La is connected in the description, the discharge lamp La can be similarly configured even when two or more discharge lamps La are connected in series or in parallel.
Further, the parallel circuit of the switching element Q1 and the diode D1 and the parallel circuit of the switching element Q2 and the diode D2 may be replaced with MOSFETs, respectively. The circuit configuration of the present embodiment can be applied regardless of whether or not the operating frequency of the inverter circuit INV changes to detect the phase advance operation. Further, regarding the form of dimming, even if the light output is continuously changed,
Further, the light output may be changed stepwise.

(Second Embodiment) This embodiment is shown in FIG.
As shown in, the negative electrode of the rectifier DB and the smoothing capacitor C1
, And the primary winding of the leakage transformer T1 is inserted between one end on the positive electrode side of the capacitor C2 and the connection point of the switching elements Q1 and Q2.
That is, the switching element that operates the chopper circuit is the switching element Q1 in the first embodiment, whereas it is the switching element Q2 in the present embodiment.

Further, the positive electrode of the rectifier DB and the capacitor C2
A diode DDB is inserted between one end of the rectifier DB and the other end of the rectifier DB, and a capacitor CDB is connected between the DC output ends of the rectifier DB. In this circuit configuration, the switching elements Q1, Q2
Since the current associated with turning on and off flows through the diode DDB, a high-speed diode with a short storage time is required for the diode DDB. However, even if the current flowing from the rectifier DB to the diode DDB is insufficient, the current flows from the capacitor CDB to the diode DDB. Since the capacitor CDB functions as a kind of buffer, it is not necessary to use a diode having a short storage time such as a switching diode as the rectifier DB. That is, generally, the diode used for rectification has a longer storage time than the diode used for switching, and the circuit configuration shown in FIG. 1 also requires a diode having a short storage time in the rectifier DB, resulting in high cost. However, by adopting the configuration of the present embodiment, a normal rectifier DB can be used, and only one high-speed diode DDB is used, so that the cost can be reduced.

Moreover, in this embodiment, the detection resistor Rs is used.
c is inserted between the switching element Q1 and the switching element Q2 to detect the detection resistor Rsc and the switching element Q2.
One end of the primary winding of the leakage transformer T1 is connected to the connection point with the. Further, unlike the first embodiment in which one end of the detection resistor Rsc is at the ground potential, the potential at the connection point with the switching element Q2 in the detection resistor Rsc depends on whether the switching elements Q1 and Q2 are on or off. Therefore, instead of the diode Df in the first embodiment, the voltage detection circuit VS for detecting the voltage across the detection resistor Rsc is provided in the present embodiment.

Further, in order to detect the period when the voltage of the AC power supply Vs is near the peak value, the first embodiment is
The power supply voltage detection circuit VD is connected to the AC power supply Vs, but in the present embodiment, the output voltage of the rectifier DB is input to the power supply voltage detection circuit VD. With this configuration, it is not necessary to provide a rectifier in the power supply voltage detection circuit VD, and the period near the peak value of the voltage of the AC power supply Vs can be detected only by comparing the divided voltage using a resistor or the like with the reference voltage. It becomes possible to do. That is, by adopting the configuration of this embodiment and extracting the period when the voltage of the AC power supply Vs is near the peak value, the power supply voltage detection circuit V shown in FIG.
Since the transformer T2 and the rectifier DB2 can be omitted from D, downsizing and cost reduction can be achieved. Other configurations and operations are similar to those of the first embodiment.

(Third Embodiment) This embodiment is shown in FIG.
As shown in, a parallel circuit of a resistor Rf and a capacitor Cf is inserted between the diode Df and the multiplier M1 in the first embodiment shown in FIG. This parallel circuit functions as a filter for removing high frequency components from the voltage half-wave rectified by the diode Df.

When the voltage waveform of the AC power supply Vs becomes as shown in FIG. 9A, the voltage across the resistor Rf (diode Df
(The voltage half-wave rectified by) changes according to the dimming depth of the discharge lamp La as shown in FIGS. 9B to 9D. Figure 9
(B) is the lighting state of the discharge lamp La at the rated lighting, (d) is the lighting state with the deepest dimming in the dimming range of the discharge lamp La, (c) is the same drawing as (b) in the same figure. The state between (d) is shown. That is, the envelope component of the voltage across the detection resistor Rsc is extracted by the resistor Rf and the capacitor Cf. If such a configuration is adopted, the detection resistor R
The responsivity of the change in the output of the comparator CP1 slightly decreases with respect to the change in the voltage across sc. Therefore, even if the voltage across the detection resistor Rsc contains some noise, it is averaged. Malfunctions will be prevented.

FIG. 10 shows the operation of this embodiment. FIG. 10A shows the voltage of the AC power supply Vs (the broken line shows the output voltage of the rectifier DB), and FIG. 10B shows the power supply voltage detection circuit. The output of VD, the same figure (c) has shown the reference voltage Vk input into the comparator CP1 and the output of the multiplier M1. Other configurations and operations are similar to those of the first embodiment.

[0047]

According to the invention of claim 1, a series circuit of a rectifier for rectifying an AC power source, a transformer having a load connected to the secondary side, and a primary winding of the transformer is provided between the DC output terminals of the rectifier. A first switching element to be inserted, a second switching element connected in series with the first switching element,
A detection resistor connected in series with the first and second switching elements, a smoothing capacitor connected in parallel to a series circuit of the first and second switching elements and the detection resistor, and first and second First and second diodes connected in parallel to the switching elements and capable of passing a current in a direction opposite to that when the respective switching elements are turned on, and the first and second diodes at a frequency sufficiently higher than the power source frequency of the AC power source. A drive circuit for alternately turning on and off the switching element; a capacitor connected between both ends of a series circuit of the primary winding of the transformer and the first switching element to form a resonance circuit together with an inductance component and a load of the transformer; The voltage across the detection resistor during the ON period of the switching element is detected near the peak value of the AC power supply voltage. When the detected voltage exceeds the reference voltage, it is determined that there is an abnormality, and an abnormality detection circuit that controls the drive circuit in a direction to eliminate the abnormality is provided. The abnormality detection circuit includes a second voltage of the voltage across the detection resistor. The current during the ON period of the switching element is detected only near the peak value of the voltage of the AC power supply, and the voltage across the detection resistor detected during this period has a substantially constant peak value regardless of the power supplied to the load. Therefore, even if the switching frequencies of the first and second switching elements are changed, the reference voltage can be set to a constant voltage close to the peak value of the voltage across the detection resistor, and as a result, the reference voltage There is an advantage that the circuit configuration required for setting is simple. Moreover, even if the switching frequency changes, the difference between the peak value of the voltage across the detection resistor when the load is normal and the reference voltage can be set to a relatively small value. It is possible to suppress the stress on the circuit components.

According to a second aspect of the present invention, in the first aspect of the present invention, the abnormality detection circuit detects the power supply voltage detection circuit for detecting a predetermined period near the peak value of the voltage of the AC power supply and the voltage across the detection resistor by half. A diode for extracting the voltage across the detection resistor generated by the current rectified by the current flowing through the detection resistor during the ON period of the second switching element, and the detection resistor detected by the power supply voltage detection circuit and extracted by the diode for the predetermined period. It consists of a multiplier that allows the voltage across both terminals to pass, and a comparator that compares the output of the multiplier with a reference voltage.By using the multiplier, the detection resistor is used only for a predetermined period near the peak value of the AC power supply voltage. It is possible to input the voltage between both ends of the
There is an advantage that the abnormality detection circuit of the invention of claim 1 can be easily realized with a relatively simple circuit configuration.

According to a third aspect of the present invention, in the second aspect of the present invention, the power supply voltage detection circuit detects a period during which the output voltage of the rectifier is equal to or higher than a set voltage, and the voltage near the peak value of the voltage of the AC power supply. Since the output voltage of the rectifier is used to detect the predetermined period, there is no need to provide a separate rectifier, and the circuit configuration is relatively simple.

According to a fourth aspect of the present invention, in the second or third aspect of the present invention, a filter circuit for removing a high frequency component from the voltage across the detection resistor is provided. Noise is removed,
There is an advantage that malfunction due to noise can be reduced.

[Brief description of drawings]

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

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

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

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

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

FIG. 6 is a specific circuit diagram of the above.

FIG. 7 is a circuit diagram showing a second embodiment of the present invention.

FIG. 8 is a circuit diagram showing a third embodiment of the present invention.

FIG. 9 is an explanatory diagram of an operation of the above.

FIG. 10 is an operation explanatory diagram of the above.

FIG. 11 is a circuit diagram showing a conventional example.

FIG. 12 is a circuit diagram showing another conventional example.

FIG. 13 is an operation explanatory diagram of the above.

FIG. 14 is an explanatory diagram of an operation of the above.

[Explanation of symbols]

C1 smoothing capacitor C2 capacitor C3 capacitor CP1 comparator Cf capacitor D1, D2 diode DB rectifier Df diode DV drive circuit La discharge lamp M1 multiplier Q1, Q2 switching element Rsc detection resistor Rf resistance T1 leakage transformer VD power supply voltage detection circuit Vs AC power supply

Claims (4)

(57) [Claims] 1. A first switching device in which a series circuit including a rectifier for rectifying an AC power source, a transformer having a load connected to a secondary side thereof, and a primary winding of the transformer is inserted between DC output terminals of the rectifier. An element, a second switching element connected in series with the first switching element, and a detection resistor connected in series with the first and second switching elements,
The smoothing capacitor connected in parallel to the series circuit of the first and second switching elements and the detection resistor, and the smoothing capacitor connected in parallel to the first and second switching elements, respectively, are in the opposite direction to the ON state of each switching element. A first and second diode through which a current can pass, a drive circuit for alternately turning on and off the first and second switching elements at a frequency sufficiently higher than the power supply frequency of the alternating current power supply, and a primary winding of a transformer A capacitor connected between both ends of the series circuit with the first switching element to form a resonance circuit together with the inductance component of the transformer and the load, and a voltage across the detection resistor during the ON period of the second switching element are supplied to the AC power supply. In the direction of detecting the voltage near the peak value, if the detected voltage exceeds the reference voltage, it is judged as abnormal and the abnormality is corrected. Power supply, characterized in that it comprises an abnormality detection circuit for controlling the dynamic circuit. 2. The abnormality detection circuit includes a power supply voltage detection circuit for detecting a predetermined period near the peak value of the voltage of the AC power supply, and a half-wave rectification of the voltage across the detection resistor to turn on the second switching element. And a diode that extracts the voltage across the detection resistor that is generated by the current flowing through the detection resistor,
7. A multiplier comprising: a multiplier for allowing a voltage across the detection resistor, which is detected by a power supply voltage detecting circuit and taken out by a diode during the predetermined period, to pass through; and a comparator for comparing the output of the multiplier with a reference voltage. 1. The power supply device according to 1. 3. The power supply device according to claim 2, wherein the power supply voltage detection circuit detects a period in which the output voltage of the rectifier is equal to or higher than a set voltage. 4. The power supply device according to claim 2, further comprising a filter circuit for removing a high frequency component from the voltage across the detection resistor.