JP2013048516A - Power factor improvement circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power factor improvement circuit capable of suppressing reduction in efficiency by reducing a loss at the time of voltage conversion.SOLUTION: In a power factor improvement circuit, control means divides the half wavelength of the rectified wave outputted from rectification means into a first area which is a part of having voltage of the rectified wave increased from 0 V, a second area which begins after the first area and ends at a part where the rectified wave passes the maximum value and descends, and a third area which begins after the second area and has voltage ending at 0 V. In the first area and the third area, a first switching element Tr1 is turned on and a control signal for switching a second switching element Tr2 is outputted, and in the second area, the second switching element Tr2 is turned off and a control signal for switching the first switching element is outputted.

Description

  The present invention relates to a power factor correction circuit used in a power supply device that supplies a constant voltage to electronic equipment, LED lighting, and the like.

  2. Description of the Related Art A circuit that rectifies and transforms an AC input voltage and outputs a DC voltage is used as a power supply device such as an electronic device or LED lighting. For example, in the case of a power supply device that outputs 100V direct current from 100V alternating current, the PFC circuit converts it to about 380V direct current, and then steps down the voltage to 100V using a DC-DC converter.

  As described above, since the PFC circuit and the DC-DC converter are passed, there is a loss when passing through the respective circuits, and the total loss is increased. In addition, since the two circuits of the PFC circuit and the DC-DC converter are provided, the circuit configuration becomes large and the manufacturing cost increases accordingly.

  Therefore, Japanese Patent Application Laid-Open No. 2004-135372 discloses first and second switching elements connected in series between outputs of a full-wave rectifier circuit and third and fourth switches connected in series between output terminals. A switching element; and a reactor (coil) connected between a node of the first and second switching elements and a node of the third and fourth switching elements, and the first switching element to the fourth switching element. A power factor correction converter is described in which the input voltage is stepped down or stepped up by performing on / off control (switching control) while synchronizing.

  Japanese Patent Laid-Open No. 11-98825 also describes a power factor correction circuit. In this power factor correction circuit, a step-up converter and a step-down converter are arranged in series, and when the input voltage is lower than a predetermined voltage, a boost operation is performed, and when the input voltage is higher than a predetermined voltage, switching included in the step-up converter is performed. The device and the switching device included in the step-down switching converter are synchronously controlled to perform step-down operation.

  By using the circuit as described above, the voltage does not need to be boosted by the PFC circuit as in the conventional power supply device, and loss can be reduced.

JP 2004-135372 A JP 11-98825 A

  However, the power factor correction converter described in Japanese Patent Application Laid-Open No. 2004-135372 has a configuration in which at least two of the four switching elements are switched synchronously, and Japanese Patent Application Laid-Open No. 11-98825 discloses. In the described power factor correction circuit, since two switching elements are switched in synchronization during the step-down operation, the efficiency due to switching decreases. In addition, since the two switching elements are configured to be switched synchronously, an element that is driven at high speed is used in a control circuit that transmits a control signal to the two switching elements, or the control signal is signal-processed. It is necessary to add a processing circuit (element), which increases the cost of the power factor correction circuit.

  Accordingly, an object of the present invention is to provide a power factor correction circuit capable of suppressing a decrease in efficiency by reducing a loss during voltage conversion.

  In order to achieve the above object, the present invention includes a rectifying means for rectifying alternating current to convert it to direct current, a first switching element, a coil, and a first diode, and stepping down the direct current voltage converted by the rectifying means. A step-up unit that includes a step-down unit, a second switching element, the coil, and a second diode, boosts a DC voltage converted by the rectifier, and turns on the first switching element and the second switching element. A power factor improving circuit for converting alternating current into direct current of an arbitrary output voltage, wherein the control means converts the half wavelength of the rectified wave output from the rectifying means to 0V A first region that is part of the portion where the voltage rises from the first region, a second region that starts after the first region and ends at a portion where the rectified wave exceeds the maximum value and the voltage drops, and begins after the second region. Voltage In the first region and the third region, the first switching element is turned on and a signal for switching the second switching element is output in the first region and the third region. The second switching element is turned off to switch the first switching element in the previous period.

  According to this configuration, a circuit for boosting to a high voltage is not required as compared to a configuration in which the voltage is once boosted to a high voltage and then stepped down to obtain a direct current of a desired voltage as in the conventional power factor correction circuit. Further, loss when boosting to a high voltage can be reduced. Further, since the voltage is boosted when the rectified voltage is low and the voltage is lowered when the rectified voltage is high, generation of harmonics can be prevented and the power factor can be improved.

  In the above configuration, the control unit changes a switching timing between the first region and the second region and / or a switching timing between the second region and the third region in accordance with the output voltage. You may do.

  In the above configuration, the control means raises the switching timing between the first region and the second region and the switching timing between the second region and the third region from a half wavelength of the rectified wave increased from 0V. You may manage in the time after starting.

  At this time, for each of the output voltages, a table storing information on the timing of switching between the first region and the second region and the timing of switching between the second region and the third region is provided, The control means may refer to the timing of switching between the first area and the second area and the timing of switching between the second area and the third area according to the output voltage from the table. Good.

  In the above-mentioned configuration, the control means switches the first region and the second region to the time when the rectified wave reaches the first voltage value, and the second region and the third region are switched. You may perform control which makes a timing the time when the said rectification wave reaches | attains the said 2nd voltage value.

  In the above configuration, a table of the first voltage value and the second voltage value set for each output voltage is provided, and the control means uses the first voltage value and the second voltage according to the output voltage from the table. You may make it refer to a voltage value.

  In the above configuration, the first switching element is disposed between an anode of the first diode and a low voltage side terminal of the rectifier, and one output side electrode of the first switching element and the One output-side electrode of the second switching element may be connected to a common node.

  In the above configuration, the third switching element is replaced with the first diode, the fourth switching element is replaced with the second diode, and the control means includes the first switching element, the second switching element, and the third switching element. A switching element that sends a control signal to the fourth switching element, and the control means turns on the fourth switching element and switches the third switching element to the first when switching the first switching element. A control signal that alternately turns on and off the switching element is output, and when the second switching element is switched, the third switching element is turned off, and a control signal that turns the fourth switching element on and off alternately with the second switching element You may make it output.

  The said structure WHEREIN: The capacitor charged with the said output voltage and the switching element which switches discharge or charge of the said capacitor may be provided.

  As a device using the above-described power factor correction circuit, for example, a lighting device including a light emitting source that emits light with a direct current, such as an LED, can be cited.

  ADVANTAGE OF THE INVENTION According to this invention, the power factor improvement circuit which can suppress the fall of efficiency and can suppress the fall of the efficiency at the time of voltage conversion can be provided.

It is a figure which shows an example of the power factor improvement circuit concerning this invention. 2 is a timing chart showing control of the control circuit shown in FIG. It is a timing chart which shows control of the control circuit in the case of controlling by a different control method using the power factor improvement circuit shown in FIG. It is a figure which shows the other example of the power factor improvement circuit concerning this invention. 5 is a control signal when the power factor correction circuit shown in FIG. 4 is boosted. 5 is a control signal when the power factor correction circuit shown in FIG. 4 is stepped down. It is a figure which shows the further another example of the power factor improvement circuit concerning this invention. It is a figure of the power supply device using the power factor improvement circuit shown in FIG. It is a figure which shows an input voltage. It is a figure which shows a rectification voltage. FIG. 9 is a control signal input to the gate of the second switching element included in the power factor correction circuit shown in FIG. 8. FIG. 9 is a control signal input to the gate of the first switching element included in the power factor correction circuit shown in FIG. 8. FIG. It is a figure which shows an input current. It is a figure which shows a rectification current. It is a figure which shows an output voltage. It is a figure which shows a rectification voltage. FIG. 9 is a control signal input to the gate of the second switching element included in the power factor correction circuit shown in FIG. 8. FIG. 9 is a control signal input to the gate of the first switching element included in the power factor correction circuit shown in FIG. 8. FIG. It is a figure which shows an output voltage. It is a figure which shows the rectified voltage when the timing which switches pressure | voltage rise operation and pressure | voltage fall operation is changed. It is a figure which shows an output voltage. It is a figure of the power supply circuit using the power factor improvement circuit shown in FIG.

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

(First embodiment)
FIG. 1 is a diagram showing an example of a power factor correction circuit according to the present invention. As shown in FIG. 1, the power factor correction circuit A includes a first input terminal In1, a second input terminal In2, a first output terminal Out1, and a second output terminal Out2. An AC power supply Pa is connected to the first input terminal In1 and the second input terminal In2 of the power factor correction circuit A through a rectifier circuit Rc (rectifier means). The alternating current from the alternating current power source Pa is converted into a direct current pulsating flow by the rectifier circuit Rc and input to the first input terminal In1 and the second input terminal In2. The high voltage side of the rectifier circuit Rc is connected to the first input terminal In1, and the low voltage side is connected to the second input terminal In2. Here, a circuit that performs full-wave rectification is employed as the rectifier circuit Rc.

  Further, an LED lamp 3 having 25 LEDs 31 connected in series is connected as a load to the first output terminal Out1 and the second output terminal Out2. The first output terminal Out1 is connected to the positive terminal of the LED lamp (the anode of the LED 31), and the second output terminal Out2 is connected to the negative terminal of the LED lamp 3 (the cathode of the LED 31). Further, the second input terminal In2 and the low voltage side of the rectifier circuit Rc are connected to the ground line (the second input terminal In2 may not be connected to the ground line).

  The power factor correction circuit A includes a first switching element Tr1, a first diode Di1, a coil L1, a second switching element Tr2, a second diode Di2, a capacitor C1, and a control circuit Cont (control means). And. The first switching element Tr1 and the second switching element Tr2 are n-type MOSFETs. In some cases, a bipolar transistor is used as the switching circuit. In this case, the source shown below is replaced with the emitter, the gate is replaced with the base, and the drain is replaced with the collector.

  The source of the first switching element Tr1 is connected to the second input terminal In2. The drain of the first switching element Tr1 is connected to the anode of the first diode Di1. The connection point between the drain of the first switching element Tr1 and the anode of the first diode Di1 is connected to the second output terminal Out2. The cathode of the first diode Di1 is connected to one end of the coil L1, and the connection point between the cathode of the first diode Di1 and the coil L1 is connected to the first input terminal In1.

  The other end of the coil L1 is connected to the drain of the second switching element Tr2 and the anode of the second diode Di2. The cathode of the second diode Di2 is connected to one terminal of the capacitor C1, and the connection point is connected to the first output terminal Out1. The other end of the capacitor C1 is connected to the second output terminal Out2. That is, the other terminal of the capacitor C1, the negative terminal of the LED lamp 3, the drain of the first switching element Tr1, and the anode of the first diode Di1 are connected to the second output terminal Out2. The source of the second switching element Tr2 is connected to the second input terminal In2. That is, the source of the first switching element Tr1 and the source of the second switching element Tr2 are connected to the second input terminal In2.

  In the power factor correction circuit A, the first switching element Tr1, the first diode Di1, and the coil L1 form a step-down converter, and the second switching element Tr2, the second diode Di2, and the coil L1 form a step-up converter. . In addition, a control signal from the control circuit Cont is input to the gates of the first switching element Tr1 and the second switching element Tr2, and on / off switching control is performed by the control signal. More specifically, the first switching element Tr1 and the second switching element Tr2 are turned on when the voltage of the signal from the control circuit Cont is at a high level, and turned off when the voltage is at a low level.

  The first switching element Tr1, the first diode Di1, and the coil L1 constitute a step-down converter that steps down and outputs an input voltage. The second switching element Tr2, the second diode Di2, and the coil L1 constitute a boost converter that boosts the input voltage. That is, the power factor correction circuit A has a configuration in which one coil L1 is shared by the step-down converter and the step-up converter.

  The power factor correction circuit A becomes a step-down converter by always turning off the second switching element Tr2. That is, the control circuit Cont transmits a Low level control signal to the gate of the second switching element Tr2, and switches the first switching element Tr1 on and off in a short time with the second switching element Tr2 turned off. By switching (switching), the voltage (rectified voltage Vpfc) rectified by the rectifier circuit Rc connected to the first input terminal In1 and the second input terminal In2 is stepped down, and the first output terminal Out1 and the second output terminal Out2 Output from.

  The power factor correction circuit A becomes a boost converter by always turning on the first switching element Tr1. That is, the control circuit Cont transmits a High level signal to the gate of the first switching element Tr1, and switches the second switching element Tr2 in a state where the first switching element Tr1 is turned on. The voltage rectified by the rectifier circuit Rc connected to In1 and the second input terminal In2 is boosted and output from the first output terminal Out1 and the second output terminal Out2.

  The circuit shown in FIG. 1 includes a capacitor C1 connected to the first output terminal Out1 and the second output terminal Out2. Since the capacitor C1 is attached, the voltage output from the coil L1 (regardless of step-down or step-up) can be smoothed and the smoothed voltage can be applied to the LED lamp 3.

  1, in the power factor correction circuit A, the source of the first switching element Tr1 and the source of the second switching element Tr2 are both connected to the second input terminal In2 (the source of the first switching element Tr1). And the source of the second switching element Tr2 is short-circuited), and the second input terminal In2 is short-circuited.

  As shown in FIG. 1, the power factor correction circuit A has a rectified voltage detection unit Svp that detects a voltage (rectified voltage Vpfc) between the first input terminal In1 and the second input terminal In2. The rectified voltage Vpfc detected by the rectified voltage detector Svp and the output voltage Vo detected by the output voltage detector Svo are input to the control circuit Cont.

  The control circuit Cont is a circuit that drives the power factor correction circuit A as a step-down converter or a step-up converter. The control circuit Cont controls on / off of the first switching element Tr1 and the second switching element Tr2, and causes the power factor correction circuit A to perform a step-down operation or a step-up operation.

  Hereinafter, the operation of the control circuit will be described with reference to the drawings. FIG. 2 is a timing chart showing control of the control circuit shown in FIG. As shown in FIG. 2, in the control circuit Cont, the rectified voltage Vpfc output from the rectifier circuit Rc has a shape in which half wavelengths of 0V or more of a sine wave are arranged.

  The half-wavelength (one peak) of the rectified voltage Vpfc shown in FIG. 2 is set to the first region F1 between the portion intersecting with 0V and the first voltage V1, and from the voltage V1 up to the second voltage V2. The second region F2 and the third region F3 until the rectified voltage Vpfc reaches 0V again from the second voltage will be described. FIG. 2 shows control signals input to the gate of the first switching element Tr1 and the second switching element Tr2.

  As shown in FIG. 2, since the rectified voltage Vpfc is low in the first region F1, the power factor correction circuit A is boosted. That is, the control circuit Cout always inputs a high level signal to the first switching element Tr1, and simultaneously inputs a signal (switching signal) that switches between the high level and the low level in a short time to the second switching element Tr2. As a result, the first switching element Tr1 is on and the second switching element Tr2 is controlled to be switched. Thereby, the power factor correction circuit A boosts the rectified voltage Vpfc and outputs it from the first output terminal Out1.

  In addition, since the rectified voltage Vpfc is high in the second region F2, the power factor correction circuit A is stepped down. That is, the control circuit Cout always inputs a low level signal to the second switching element Tr2, and simultaneously inputs a signal (switching signal) that switches between the high level and the low level in a short time to the first switching element Tr1. Thereby, the second switching element Tr2 is off, and the first switching element Tr1 is controlled to be switched. Thereby, the power factor correction circuit A steps down the rectified voltage Vpfc and outputs it from the first output terminal Out1.

  As shown in FIG. 2, the rectified voltage Vpfc is small in the third region F3. The power factor correction circuit A is boosted. The control circuit Cout always inputs a high level signal to the first switching element Tr1, and simultaneously inputs a signal (switching signal) that switches between the high level and the low level in a short time to the second switching element Tr2. As a result, the first switching element Tr1 is on and the second switching element Tr2 is controlled to be switched. Thereby, the power factor correction circuit A boosts the rectified voltage Vpfc and outputs it from the first output terminal Out1.

  As shown in FIG. 2, in the power factor correction circuit A, the voltage is boosted in the region where the rectified voltage Vpfc is low (first region F1 and third region F3), and in the region where the rectified voltage Vpfc is high (second region F2). By stepping down the voltage, the waveform of the current value flowing through the first input terminal In1 can be shaped along the waveform of the rectified voltage Vpfc, thereby improving the power factor.

  Further, since only one of the first switching element Tr1 and the second switching element need be switched, the loss due to switching of the switching element can be reduced. Further, since the two switching elements do not have to be switched synchronously, there is no need to operate the control circuit at high speed, and accordingly, the configuration of the control circuit can be simplified and the cost can be reduced.

  Thus, by determining the two voltages, it is possible to output an accurate output voltage even if the frequency and amplitude of the AC voltage from the AC power supply Pa vary. In addition, since the output voltage can be adjusted by appropriately changing the first voltage V1 and the second voltage V2, even if the frequency and amplitude of the AC voltage from the AC power supply Pa vary, the desired voltage can be obtained by simple control. Can be output.

  FIG. 3 is a timing chart showing control of the control circuit in the case where control is performed by a different control method using the power factor correction circuit shown in FIG. In the timing chart shown in FIG. 3, the timing at which the first region F1 and the second region F2 are switched is as follows. When the time T1 has elapsed after the rectified voltage Vpfc starts to rise from 0 V, the second region F2 and the third region F3 The switching timing is managed in terms of time as the time T2 has elapsed since switching to the second region F2.

  As described above, the power factor correction circuit A performs a step-up operation in the first region and the third region, and performs a step-down operation in the second region. In this way, switching between the step-up operation and the step-down operation over time can be performed at an accurate timing. From this, it is possible to output a direct current that accurately matches a desired voltage. Further, since only the time is adjusted, the control of the control circuit Cont can be simplified.

  Note that the method of managing the time and switching the step-up operation or the step-down operation in this way is suitable when an alternating current with a small variation in frequency and amplitude is supplied from the alternating current power source Pa or when the load is used in a state where the load is hardly changed. ing.

  In other words, since the data size can be reduced by using the circuit for supplying power to a highly accurate input voltage or a load with little fluctuation, the size and the size can be simplified. Further, since the step-up operation and the step-down operation are switched over time, the control is simple.

  In the present embodiment, the first region, the second region, and the third region are fixed regions, but either the first region or the third region (in other words, one of the switching timings of the step-up operation and the step-down operation). It is possible to change the output voltage by fixing one) and changing the other. This facilitates control of the output voltage. Further, when the load does not change like an LED lamp, a lookup table for each voltage can be used, and the data size of the table necessary for control can be reduced accordingly.

(Second Embodiment)
Another example of the power factor correction circuit according to the present invention will be described with reference to the drawings. FIG. 4 is a diagram showing another example of the power factor correction circuit according to the present invention. As shown in FIG. 4, the power factor correction circuit B has a configuration in which the first diode Di1 of the power factor correction circuit A shown in FIG. 1 is replaced with a third switching element Tr3 and the second diode Di2 is replaced with a fourth switching element Tr4. is there. Further, the control circuit Cont is configured to transmit a control signal to the third switching element Tr3 and the fourth switching element Tr4. Other than that, it has the same configuration as the power factor correction circuit A, and substantially the same parts are denoted by the same reference numerals and detailed description of the same parts is omitted.

  As described above, the power factor correction circuit B includes the third switching element Tr3 and the fourth switching element Tr4 in addition to the first switching element Tr1 and the second switching element Tr2.

  In the power factor improving circuit B, the second switching element Tr2 and the fourth switching element Tr4 are alternately turned on / off in a state where the first switching element Tr1 is turned on and the third switching element Tr3 is turned off. Works as.

  Control signals supplied to the respective switching elements at this time will be described with reference to the drawings. FIG. 5 shows control signals when the power factor correction circuit shown in FIG. 4 is boosted. As shown in FIG. 5, the control signal Cont always receives a high-level control signal from the control circuit Cont and the third switching element Tr3 receives a control signal always at the low level. As a result, the first switching element Tr1 is always on, and the third switching element Tr3 is always off.

  In this state, when a high level control signal is input to the second switching element Tr2, a low level control signal is input to the fourth switching element Tr4. Conversely, when a low level control signal is input to the second switching element Tr2, a high level control signal is input to the fourth switching element Tr4. That is, the second switching element Tr2 and the fourth switching element Tr4 are driven such that when one is on, the other is off, and when one is off, the other is on (synchronous switching).

  In the power factor correction circuit B, the first switching element Tr1 and the third switching element Tr3 are alternately turned on / off while the second switching element tr2 is turned off and the fourth switching element Tr4 is turned on. Operates as a buck converter.

  Control signals supplied to the respective switching elements at this time will be described with reference to the drawings. FIG. 6 shows control signals when the power factor correction circuit shown in FIG. 4 is stepped down. As shown in FIG. 6, the control signal Cont always receives a low-level control signal from the control circuit Cont and the fourth switching element Tr4 always receives a high-level control signal. Thereby, the second switching element Tr2 is always off, and the fourth switching element Tr4 is always on.

  In this state, when a high level control signal is input to the first switching element Tr1, a low level control signal is input to the third switching element Tr3. Conversely, when a low level control signal is input to the first switching element Tr1, a high level control signal is input to the third switching element Tr3. That is, the first switching element Tr1 and the third switching element Tr3 are driven such that when one is on, the other is off, and when one is off, the other is on (synchronous switching).

  Similar to the power factor correction circuit A, in the power factor correction circuit B, the control circuit Cont has the first switching element Tr1 to the fourth switching element when the rectified voltage Vpfc, which is the output voltage from the rectifier circuit Rc, is lower than the output voltage Vo. A control signal for performing a boosting operation as shown in FIG. 5 is transmitted to Tr4. When the rectified voltage Vpfc is higher than the output voltage Vo, the control circuit Cont transmits a control signal for performing a step-down operation as shown in FIG. 6 to the first switching element Tr1 to the fourth switching element Tr4.

  As a result, the power factor can be improved, and when performing the step-up operation or the step-down operation, the two switching elements are turned on and the other two switching elements are synchronized with the other turned off. It is only necessary to perform switching, and the number of synchronized switching elements is small, so that the control circuit Cont can be simplified accordingly.

(Third embodiment)
Still another example of the power factor correction circuit according to the present invention will be described with reference to the drawings. FIG. 7 is a diagram of still another example of the power factor correction circuit according to the present invention. The power factor correction circuit C shown in FIG. 7 includes a flicker prevention capacitor C2 and a flicker prevention switching element Tro on the output side. The other parts have the same configuration as that of the power factor correction circuit A shown in FIG. 1, and substantially the same parts are denoted by the same reference numerals and detailed description of the same parts is omitted.

  The power factor correction circuit C is a circuit that converts alternating current into direct current and outputs it. In Japan, the frequency of alternating current is 50 Hz in eastern Japan and 60 Hz in western Japan, and the output of the power factor correction circuit is direct current, but fluctuates between 50 Hz and 60 Hz. When the LED lamp 3 is turned on with fluctuation direct current, the LED lamp 3 (LED 31) flickers. Such a flicker can be eliminated by increasing the capacitance of the capacitor C1 in the power factor correction circuit A. However, the larger the capacitance, the larger the volume and the higher the cost of the capacitor. Hinders

  Therefore, in order to suppress such flickering of the LED 31, the power factor correction circuit C shown in FIG. 7 connects the first output terminal Out1 and the second output terminal Out2, that is, the LED lamp 3 as a load. The anti-flickering capacitor C2 is connected in parallel, and the anti-flickering switching element Tro is disposed between the cathode of the second diode Di2 and one terminal of the anti-flickering capacitor C2. As shown in FIG. 7, the flicker prevention capacitor C2 is attached to the output side of the capacitor C1. Further, the flicker prevention switching element Tro is arranged between one terminal of the capacitor C1 and one terminal of the flicker prevention capacitor C2.

  Here, a method of suppressing flicker by the power factor correction circuit C will be described. When the output of the power factor correction circuit C (current value of the output current) fluctuates between 50 Hz and 60 Hz, the light emission luminance of the LED 31 also fluctuates between 50 Hz and 60 Hz. When the light emission luminance is switched at a frequency of 60 Hz or less, the human eye visually recognizes the switching as flickering. Therefore, the current supplied to the LED lamp 3 is made constant in a minute time by switching the flicker prevention switching element Tro at a high speed. As the operating frequency of the flicker prevention switching element Tro, flicker can be suppressed by setting it to a frequency (approximately 200 Hz) or more that is not recognized by human eyes. The flicker prevention switching element Tro is ON / OFF controlled by a signal from the control circuit Cont. Note that the switching element Tro for preventing flickering switches at 1 MHz or less because switching loss increases when the switching is performed at 1 MHz or more and the control becomes complicated.

  Further, since the operating frequency of the flicker prevention switching element Tro is high and a constant current has only to be supplied in a very short time, it is necessary to light the LED lamp 3 even if the capacitance of the capacitor C1 and the flicker prevention capacitor C2 is small. Current can be supplied.

  From the above, the power factor improvement circuit C can improve the power factor as well as the power factor improvement circuit A, and can reduce loss due to switching of the switching element. Further, since the two switching elements do not have to be switched synchronously, there is no need to operate the control circuit at high speed, and accordingly, the configuration of the control circuit can be simplified and the cost can be reduced. Furthermore, it is possible to prevent the flickering of the LED without using a large-capacity capacitor or using a special circuit.

  In the present embodiment, the flicker prevention switching element Tro is disposed on the first output terminal side (the anode side of the LED lamp 3), but is disposed on the second output terminal side (the cathode side of the LED lamp 3). However, it is possible to provide a power factor correction circuit that performs the same operation.

(First embodiment)
An embodiment using the power factor correction circuit according to the present invention as described above will be described with reference to the drawings. FIG. 7 is a diagram of a power supply device using the power factor correction circuit according to the present invention. As shown in FIG. 7, the power supply device Ps includes a power factor correction circuit A, an AC power source Pa, an AC voltage detector Svi that detects an input voltage Vin from the AC power source Pa, and an input current Iin from the AC power source Pa. An AC current detector Sai for detecting a rectifier, a rectifier circuit Rc for full-wave rectification of AC from the AC power supply Pa, a rectified voltage detector Svp for detecting a rectified voltage Vpfc rectified by the rectifier circuit Rc, and a first input terminal A rectified current detector Sap for detecting the rectified current Ipfc flowing in In1 and an output voltage detector Svo for detecting the output voltage Vout of the power factor correction circuit are provided.

  An example of boosting operation of the power supply device Ps shown in FIG. 7 will be described with reference to the drawings. 8 is a diagram showing the input voltage, FIG. 9 is a diagram showing the rectified voltage, and FIG. 10 is a control signal inputted to the gate of the second switching element included in the power factor correction circuit shown in FIG. 11 is a control signal input to the gate of the first switching element included in the power factor correction circuit shown in FIG. 7, FIG. 12 is a diagram showing the input current, and FIG. 13 is a diagram showing the rectified current. FIG. 14 is a diagram showing the output voltage. In FIGS. 10 and 11, the vertical axis indicates that 1 is a high level and 0 is a low level.

  As shown in FIG. 8, the AC power supply Pa inputs an AC voltage having a frequency f = 50 Hz and an effective voltage value Vrms = 100 V (peak value of about 140 V) to the rectifier circuit Rc. When this AC voltage is full-wave rectified by the rectifier circuit Rc, a positive voltage pulse wave as shown in FIG. 9 is obtained.

  The control circuit Cont acquires the rectified voltage Vpfc from the rectified voltage detector Svp. While the rectified voltage Vpfc changes from 0 V to 100 V (corresponding to the first voltage V1) (during the first region), the control circuit Cont inputs a high level signal to the gate of the first switching element Tr1. Then, a signal (switching signal, see FIG. 10) for switching between the high level and the low level in a short time is input to the gate of the second switching element Tr2.

  Since the first switching element Tr1 is on and the second switching element Tr2 is switched, the power factor correction circuit A performs a boost operation.

  When the rectified voltage Vpfc rises and exceeds 100 V (first voltage V1), the control circuit Cont inputs a low level signal to the gate of the second switching element Tr2 and switches the switching signal to the gate of the first switching element Tr1. (See FIG. 11). As a result, the second switching element Tr2 is off and the first switching element Tr1 is switched, so that the power factor correction circuit A is stepped down. The power factor correction circuit A performs a step-down operation until the rectified voltage Vpfc reaches 60 V (during the second region).

  Then, while the rectified voltage Vpfc is between 60 V and 0 V (during the third region), a high level signal is input to the gate of the first switching element Tr1, and the high level is input to the gate of the second switching element Tr2 in a short time. And a signal for switching between low level and low level (switching signal, see FIG. 10).

  As described above, by boosting or stepping down the rectified voltage Vpfc by the power factor correction circuit A and smoothing it by the capacitor C1, it is possible to output a substantially constant output voltage as shown in FIG. In addition, by increasing the voltage when the rectified voltage Vpfc is small and by decreasing the voltage when the rectified voltage Vpfc is large, it is possible to prevent current from flowing easily or flowing a large current in a short time. Thereby, the input current Iin from the AC power source Pa and the rectified current Ipfc from the rectifier circuit Rc have waveforms as shown in FIGS. 12 and 13, respectively. The waveform of the input current Iin shown in FIG. 12 is similar to the input voltage Vin, and the waveform of the rectified current Ipfc shown in FIG. 13 is approximate to the rectified voltage Vpfc, and the power factor correction circuit A is a PFC circuit. It can be seen that the power factor has been improved.

(Second embodiment)
The second embodiment is the same as the first embodiment except that the control method is different, and substantially the same parts are denoted by the same reference numerals. 15 is a diagram showing the rectified voltage, FIG. 16 is a control signal input to the gate of the second switching element included in the power factor correction circuit shown in FIG. 7, and FIG. 17 is a power factor improvement shown in FIG. FIG. 18 is a diagram illustrating an output voltage, which is a control signal input to the gate of the first switching element included in the circuit.

  In the second embodiment, an AC voltage having the same frequency as that of the first embodiment (as shown in FIG. 8) and having a frequency f = 50 Hz and an effective voltage value Vrms = 100 V (peak value about 140 V) is input to the rectifier circuit Rc. ing. When this AC voltage is full-wave rectified by the rectifier circuit Rc, a positive voltage pulse wave as shown in FIG. 9 is obtained.

  The control circuit Cont acquires the rectified voltage Vpfc from the rectified voltage detector Svp. As shown in FIG. 15, the control circuit Cont inputs a high-level signal to the gate of the first switching element Tr1 for 2.5 ms (during the first region) after the rectified voltage Vpfc starts to rise from 0V. Then, a signal for switching between the high level and the low level in a short time is input to the gate of the second switching element Tr2 (see FIG. 16).

  While the rectified voltage Vpfc starts to rise from 0V and exceeds 2.5 ms to 8.5 ms (during the second region), the control circuit Cont inputs a low level signal to the gate of the second switching element Tr2, A switching signal (see FIG. 17) is input to the gate of the first switching element Tr1. As a result, the second switching element Tr2 is off and the first switching element Tr1 is switched, so that the power factor correction circuit A is stepped down.

  Then, the rectified voltage Vpfc starts to increase from 0V and exceeds 8.5 ms to 10 ms (during the third region), while inputting a High level signal to the gate of the first switching element Tr1, the second switching element Tr2 A signal (switching signal, see FIG. 16) for switching between the high level and the low level in a short time is input to the gate of the first gate.

  Thus, by controlling the power factor correction circuit A, a DC voltage of about 72 V is output as shown in FIG.

  FIG. 19 is a diagram showing the rectified voltage when the timing for switching between the step-up operation and the step-down operation is changed, and FIG. 20 is a diagram showing the output voltage. As illustrated in FIG. 19, the second region is set to 2.5 ms to 6.0 ms (between 3.5 ms), and during that time, the control circuit Cont inputs a low level signal to the gate of the second switching element Tr2, A switching signal is input to the gate of the first switching element Tr1. As a result, the second switching element Tr2 is off and the first switching element Tr1 is switched, so that the power factor correction circuit A is stepped down.

  The third region is set to 6.0 ms to 10 ms (4 ms), and during that time, a high level signal is input to the gate of the first switching element Tr1, and a high level and a low level are quickly input to the gate of the second switching element Tr2. Input a signal for switching between and.

  Thus, by controlling the power factor correction circuit A, a DC voltage of about 90 V is output as shown in FIG.

  From the above, the output voltage can be changed by fixing the switching timing of the first region and the first region and changing the switching timing of the second region and the third region. In this embodiment, the switching timing of the first area and the second area is fixed, but the switching timing of the first area and the second area is changed, and the switching timing of the second area and the third area is changed. Needless to say, it is the same even if fixed.

  When the alternating current waveform from the alternating current power supply Pa is always constant, a lookup table for the first region, the second region, and the third region is prepared according to the output voltage, and the table is read out according to the desired output voltage. It is also possible to do.

(Third embodiment)
Another embodiment using the power factor correction circuit according to the present invention as described above will be described with reference to the drawings. FIG. 22 is a diagram of a power supply device using the power factor correction circuit shown in FIG. The power factor correction circuit C according to the present invention is a circuit that converts AC into DC and outputs the result.

  The power supply device Ps2 has the same configuration as the power supply device Ps shown in FIG. 8 except that it uses the power factor correction circuit C and includes an output current detector Sao that detects the output current Aout. The same parts are denoted by the same reference numerals, and detailed description of the same parts is omitted.

  The control circuit Cont detects the output current detected by the output current detector Sao, and switches the flicker prevention switching element Tro on and off based on the output current. More specifically, the flicker prevention switching element Tro is controlled so that the average current becomes constant within a very short time by the current detected by the output current detector Sao.

  A case where the flicker prevention switching element Tro is operated at 10 kHz will be described. For example, if the current value detected by the output current detector Sao is 10 A and the average value of the current supplied to the LED lamp 3 is 1 A, the control circuit Cont sets the flicker prevention switching element Tro to an on-duty of 0.1. (The flicker prevention switching element Tro has an on time of 0.1 ms and an off time of 0.9 ms).

  At this time, the flicker prevention capacitor C2 is charged for 0.1 ms, and discharged for 0.9 ms, so that a current is supplied to the LED lamp 3 and the LED 31 emits light. When the LED 31 emits light, the flickering prevention capacitor C2 is discharged, the current value changes, and the brightness of the LED 31 decreases (when the capacity of C2 is small, the capacitor is discharged within 0.9 ms, and the current flows to the LED lamp 3). No longer supplied). The frequency at this time is 10 kHz, and cannot be recognized by human eyes, and the flickering of the LED 31 can be suppressed.

  Similarly, when the output current detector Sao is 2 A, the LED lamp 3 is supplied with an average current of 1 A by driving at an on-duty of 0.5. Also in this case, since the LED 31 is repeatedly turned on and off at high speed, flickering of the LED 31 cannot be recognized by human eyes.

  In the above-described example, an example in which the flicker prevention switching element Tro is driven at 10 kHz has been described. However, the present invention is not limited to this, and 200 Hz, which cannot be recognized by human eyes. That is all you need. In consideration of ease of control, the upper limit is preferably about 1 MHz.

  The first switching element Tr1 and the second switching element Tr2 are controlled such that the output current from the power factor correction circuit is higher than the average value of the current supplied to the LED lamp 3. This is because, for example, when the output current from the power factor correction circuit has the same average value of the current supplied to the LED lamp 3, the on-duty of the flicker prevention switching element Tro becomes 1, and the flicker prevention switching element Tro is always on. This is because the flicker prevention effect is lost.

  As described above, by using the power factor correction circuit according to the present invention, the switching control can be simplified and the configuration of the control circuit can be simplified. In addition, since there is no need to boost the voltage with a PFC circuit as in the conventional circuit, a decrease in efficiency during voltage conversion can be suppressed accordingly. Furthermore, when switching two switching elements, synchronous switching is not required, so it is possible to suppress losses due to synchronous switching of the switching elements, and it is possible to suppress a decrease in efficiency during voltage conversion. It is.

  Further, although the MOSFET is used as the switching element described above, the present invention is not limited to this, and for example, a switching element such as a bipolar transistor, a MOS transistor, or an IGBT can be widely used.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The embodiments of the present invention can be variously modified without departing from the spirit of the invention.

  The illumination power supply circuit according to the present invention can be used in an illumination device that adjusts illuminance (brightness) by lighting with a direct current such as an LED or an organic EL and changing an on / off duty.

Tr1 first switching element Tr2 second switching element Di1 first diode Di2 second diode Cont control circuit C1 capacitor L1 coil 3 LED lamp 31 LED

Claims (10)

Rectifying means for rectifying alternating current and converting it into direct current;
A step-down unit including a first switching element, a coil, and a first diode, for stepping down a DC voltage converted by the rectifier;
A boosting unit that boosts a direct-current voltage converted by the rectifying means, including a second switching element, the coil, and a second diode;
Control means for controlling on / off of the first switching element and the second switching element, and a power factor correction circuit for converting alternating current into direct current of an arbitrary output voltage,
The control means sets the half wavelength of the rectified wave output from the rectifying means to a first region that is a part of a portion where the voltage rises from 0 V, and the rectified wave that starts after the first region exceeds the maximum value. Divided into a second region that ends at the part where the voltage drops and a third region that starts after the second region and reaches the voltage of 0V,
In the first region and the third region, the first switching element is turned on and a control signal for switching the second switching element is output. In the second region, the second switching element is turned off. A power factor correction circuit, characterized by outputting a control signal for switching the first switching element.   2. The control means changes a switching timing between the first area and the second area and / or a switching timing between the second area and the third area in accordance with the output voltage. Power factor correction circuit described in 1.   The control means determines the switching timing between the first region and the second region and the switching timing between the second region and the third region after the half wavelength of the rectified wave starts to rise from 0V. 3. The power factor correction circuit according to claim 1, wherein the power factor improvement circuit is managed by time. A table storing information on the switching timing of the first region and the second region and the switching timing of the second region and the third region for each output voltage;
The said control means refers to the switching timing of the said 1st area | region and the said 2nd area | region according to output voltage from the said table, and the switching timing of the said 2nd area | region and the said 3rd area | region. Power factor correction circuit.   The control means sets a timing at which the first region and the second region are switched as a time when the rectified wave reaches the first voltage value, and a timing at which the second region and the third region are switched as the rectification. 3. The power factor correction circuit according to claim 1, wherein the power factor correction circuit is a time point when a wave reaches the second voltage value. 4. A table storing information of the first voltage value and the second voltage value for each output voltage;
6. The power factor correction circuit according to claim 5, wherein the control means refers to a first voltage value and a second voltage value corresponding to an output voltage from the table.   The first switching element is disposed between an anode of the first diode and a low voltage side terminal of the rectifying means, and one output side electrode of the first switching element and the second switching element The power factor correction circuit according to any one of claims 1 to 6, wherein one of the output electrodes is connected to a common node. A third switching element instead of the first diode, a fourth switching element instead of the second diode;
The control means sends a control signal to the first switching element, the second switching element, the third switching element, and the fourth switching element;
The control means outputs a control signal for turning on the fourth switching element and turning on and off the third switching element alternately with the first switching element when switching the first switching element; The power factor according to any one of claims 1 to 6, wherein a control signal that turns off the third switching element and turns on and off the fourth switching element alternately with the second switching element is output when switching the power supply. Improvement circuit. A capacitor charged with the output voltage;
The power factor correction circuit according to claim 1, further comprising a switching element that switches discharging or charging of the capacitor.   An illumination apparatus using the power factor correction circuit according to any one of claims 1 to 9.

Images