JP2008193818A - Power factor improving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power factor improving circuit which can switch a current critical mode and a current continuous mode without needing a slope compensation for countermeasure to subharmonics. <P>SOLUTION: The power factor improving circuit has a rectifying means DB1 which rectifies AC voltage, a transformer T1 which has primary winding Np and secondary winding Nc, and a main switching element Q1 connected to the above primary winding. It is equipped with a zero current detecting means 16 which is connected to the above secondary winding and detects the above main switch having turned off and detects the primary winding current having vanished during the OFF period of the above main switching element, and a current continuous mode operating means 2 which generates triangular wave signals from voltage generated in the above secondary winding and turns on the above main switching element forcedly thereby operating it in the current continuous mode, ignoring the detection results of the zero current detecting means, when the peak value of this triangular wave signal gets over a set value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power factor correction circuit used for a switching power supply.

  Conventional power factor correction circuits are classified into a current critical type and a current continuous type. In the current critical type, when the output power is large and the input voltage is low, the oscillation frequency of the main switching element is lowered, choke howling occurs, and the current peak of the main switching element and the choke is increased. Since the current execution value increases, the efficiency decreases, so that it is suitable for a power factor improvement circuit with a low power up to 300 W, but not suitable for a power factor improvement circuit with a large power of 300 W or more. On the other hand, the continuous current type has a large switching loss of the main switching element. Therefore, it is suitable for a power factor improvement circuit with a large power of 300 W or more that is not greatly affected by this problem. Not suitable for.

As a means for solving such a problem, a power factor improvement circuit including a switching means that operates in a current critical mode and switches to a current continuous mode by fixing the frequency when a certain output voltage is reached (Patent Document 1) A power factor correction circuit having switching means for switching between a current critical mode and a current continuous mode when a certain output power is reached by fixing the off period of the main switching element has been developed (Patent Document 2). reference).
Japanese Patent Laid-Open No. 2005-20994 US Patent Application Publication No. 2004/263140

  However, when switching means for switching between the current critical mode and the current continuous mode is provided with the frequency fixed, subharmonics are generated when the on-duty of the main switching element is 50% or more. Slope compensation is necessary for this subharmonic countermeasure.

  In addition, when the switching means for switching between the current critical mode and the current continuous mode is provided while fixing the OFF period of the main switching element, the oscillation frequency does not decrease when the input / output voltage difference is small, such as the 200 V system input. Because the current peak of the main switching element is also small, the current critical mode is more efficient, but the off time is widened and it becomes easier to operate in the current continuous mode, and the switching means between the current critical mode and the current continuous mode is stopped. There was a need to do.

  The present invention has been made in view of the above problems, and does not require slope compensation for subharmonic countermeasures, and has a power factor correction circuit capable of continuously switching between a current critical mode and a current continuous mode. provide.

  In order to solve the above problems, a power factor correction circuit according to the present invention includes rectifying means for rectifying and supplying an AC voltage, a primary winding and a secondary winding, and one end of the primary winding is the Connected to a transformer connected to the rectifier and a main switching element connected to the other end of the primary winding of the transformer, and repeatedly turned on by the main switching element at a cycle faster than the cycle of the AC voltage. A power factor correction circuit that turns off and controls the output voltage of the rectifier, and is connected to the secondary winding, detects that the main switching element is turned off, and turns off the main switching element A triangular current signal is generated from zero current detecting means for detecting that the primary winding current has become zero during the period and the voltage generated in the secondary winding, and the peak value of the triangular wave signal is equal to or greater than a set value. Sometimes said Z Characterized by comprising a current continuous mode operation means for operating in a continuous current mode is forcibly turns on the main switching element ignores the detection result of the current detecting means.

The continuous current mode operation means includes a switching element, generates a triangular wave signal from a voltage generated in the secondary winding, and turns on the switching element when a peak value of the triangular wave signal exceeds a set value. The main switching element is forcibly turned on.
The continuous current mode operation means includes an OR circuit, generates a triangular wave signal from a voltage generated in the secondary winding, and outputs the triangular wave signal from the OR circuit when a peak value of the triangular wave signal becomes a set value or more. An on signal is forcibly oscillated to the switching element to turn on the main switching element.
The continuous current mode operation means includes a capacitor, and is configured to generate a triangular wave signal by charging and discharging based on a voltage generated in the secondary winding.

  According to the present invention, the triangular wave signal is generated from the voltage generated in the secondary winding of the transformer having the primary and secondary windings that are magnetically coupled, and the peak value of the triangular wave signal is greater than the set value. Sometimes, the main switching element is forcibly turned on and operated in the continuous current mode ignoring the detection result of the zero current detecting means for detecting that the primary winding current becomes zero during the OFF period of the main switching element. By providing the continuous current mode operation means, it is possible to take advantage of each mode by operating in the current critical mode at light loads and in the continuous current mode at heavy loads. Therefore, there is an effect that no slope compensation is required.

  Further, according to the present invention, for example, even when the input / output voltage difference is small, such as a 200V system input, the positive voltage of the secondary winding is small, the negative voltage is large, and the level of the triangular wave signal is increased. Therefore, there is an effect that the current continuous mode is hardly obtained and the operation can be smoothly performed in the current critical mode.

  Embodiments according to the power factor correction circuit of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a power factor correction circuit according to the present invention. As shown in FIG. 1, the power factor correction circuit according to one embodiment of the present invention includes a diode bridge DB1 (rectifying means), a transformer T1, a switching element Q1, a diode D1, capacitors C1 and C13, and a resistor R1. To R10 and the control circuit 1.

  The diode bridge DB1 forms a rectifier circuit and rectifies AC power input from an outlet. The transformer T1 has a primary winding Np and a secondary winding Nc that are electromagnetically coupled to each other. The main switching element Q1 is composed of a MOSFET and has a drain and a source as first and second main terminals and a gate as a control electrode.

  One end of the input end ACinput is connected to one AC input end of the diode bridge DB1. The other end of the input end ACinput is connected to the other AC input end of the diode bridge DB1. The positive DC output terminal of the diode bridge DB1 is connected to one terminal of the resistor R1. The other end of the resistor R1 is connected to one end of the capacitor C1, the negative side of the primary winding Np of the transformer T1, and one end of the resistor R2.

  The positive side of the primary winding Np of the transformer T1 is connected to the drain of the main switching element Q1 and the anode of the diode D1. The cathode of the diode D1 is connected to the positive side of the capacitor C13, the positive voltage end + V of the output end Output, and one end of the resistor R8.

  The negative DC output terminal of the diode bridge DB1 is connected to the other terminal of the capacitor C1, one terminal of the resistors R6 and R7, the negative electrode side of the capacitor C13, and the negative voltage terminal -V of the output terminal Output.

  The other end of the resistor R2 is connected to one end of the resistor R3 and the input end A of the control circuit 1. The other end of the resistor R3 is grounded to the ground potential. The resistors R2 and R3 serve as input side voltage dividing resistors.

  The negative electrode side of the secondary winding Nc of the transformer T1 is grounded to the ground potential. The positive side of the secondary winding Nc of the transformer T1 is connected to one end of the resistor R4. The other end of the resistor R4 is connected to the input end B of the control circuit 1. The source of the main switching element Q1 is connected to the input terminal C of the control circuit 1 through the other end of the resistor R7 and the resistor R10. The resistor R7 is a current detection resistor for detecting the switching current IQ1 of the main switching element Q1.

  The other end of the resistor R8 is connected to one end of the resistor R9 and the input end D of the control circuit 1. The other end of the resistor R9 is grounded to the ground potential. The resistors R8 and R9 form output side voltage dividing resistors.

  The gate of the main switching element Q1 is connected to one end of the resistor R5 and the other end of the resistor R6. The other end of the resistor R5 is connected to the output end E of the control circuit 1.

  The control circuit 1 includes a driver 11, a comparator 12 (switching element current detection means), a multiplier 13, an RS flip-flop 15, a comparator 16 (zero current detection means), and an amplifier 17 (output voltage detection means). , A one-shot multivibrator (OSMV: monostable multivibrator) 19 and constant voltage sources E16 and E17, and the main switching element Q1 is turned on / off based on signals input at the input terminals A to D The voltage VGS for generating the voltage VGS is generated and the output operation is performed from the output terminal E.

  One input end of the multiplier 13 is connected to the input end A of the control circuit 1. The positive output terminal of the constant voltage source E17 is connected to the positive input terminal of the amplifier 17, and the negative output terminal of the constant voltage source E17 is grounded to the ground potential. The negative input terminal of the amplifier 17 is connected to the input terminal D of the control circuit 1. The other input end of the multiplier 13 is connected to the output end of the amplifier 17. The negative input terminal of the comparator 12 is connected to the output terminal of the multiplier 13. The positive input terminal of the comparator 12 is connected to the input terminal C of the control circuit 1, and the output terminal of the comparator 12 is connected to the reset terminal R of the RS flip-flop 15.

  The positive output terminal of the constant voltage source E16 is connected to the negative input terminal of the comparator 16, and the negative output terminal of the constant voltage source E16 is grounded to the ground potential. The positive input terminal of the comparator 16 is connected to the input terminal B of the control circuit 1, and the output terminal of the comparator 16 is connected to the input terminal of the OSMV 19. The output terminal of the OSMV 19 is connected to the set terminal S of the RS flip-flop 15. The output terminal Q of the RS flip-flop 15 is connected to the input terminal of the driver 11, and the output terminal of the driver 11 is connected to the output terminal E of the control circuit 1.

  The multiplier 13 multiplies the voltage MULT input from the input terminal A by the comparison result between the voltage input from the input terminal D by the amplifier 17 and the output voltage of the constant voltage source E17, and outputs the result to the comparator 12. The comparator 12 compares the voltage input from the input terminal C with the multiplication result input from the multiplier 13 and outputs the comparison result to the reset terminal R of the RS flip-flop 15.

  The comparator 16 compares the voltage input from the input terminal B with the comparison result between the output voltage of the constant voltage source E16 and outputs the comparison result to the OSMV 19. The OSMV 19 outputs a low level signal to the set terminal S of the RS flip-flop 15 when a signal that maintains a constant level or a signal that rises from a low level to a high level is input, but a signal that falls from a high level to a low level. When input, a signal (pulse) that is at a low level before the falling of the signal, becomes a high level for a certain time in synchronization with the rising, and then returns to a low level is output to the set terminal S of the RS flip-flop 15 To do.

  The RS flip-flop 15 performs a set operation or a reset operation on the output terminal Q based on the voltage input to the reset terminal R or the set terminal S. The driver 11 is composed of a switching circuit using a transistor, for example, and at a frequency (switching frequency) higher than the frequency of the alternating current input to the switching power supply 1 based on the voltage at the output terminal Q of the RS flip-flop 15. The main switching element Q1 is turned on / off. The driver 11 turns on the main switching element Q1 when a high level signal is inputted, and turns off the main switching element Q1 when a low level signal is inputted. As described above, the configuration of the driver 11 is not limited as long as the gate of the main switching element Q1 can be turned on / off.

  The power factor correction circuit according to the present embodiment operates in the continuous current mode by forcibly turning on the main switching element Q1 ignoring the detection result of the zero current detection means (comparator 16) separately from the control circuit 1. A continuous current mode operation circuit 2 is provided. The continuous current mode operation circuit 2 includes a comparator 21, a switching element Q2 composed of a MOSFET, a constant voltage source E21, a Schottky barrier diode SBD, a capacitor C21, and a resistor R21.

  The secondary winding Nc of the transformer T1 is connected to a resistor R21, and this resistor R21 is connected to the positive input terminal of the comparator 21 so as to input a voltage generated in the secondary winding Nc. Further, the resistor R21, the capacitor C21 having one end connected to the ground terminal of the main circuit of the power factor correction circuit, and the positive input end of the comparator 21 are connected in series. A triangular wave signal is generated from the winding Nc.

  At this time, when the input voltage is high and the difference between the output voltage and the output voltage is small, the positive voltage of the secondary winding Nc decreases and the negative voltage increases. As a result, the charging current of the capacitor C21 is small and the discharging current is large, and the triangular wave voltage of the capacitor C21 is reduced to a negative voltage. At this time, a current flows from the A terminal of the control circuit 1 to the capacitor, causing a malfunction of the control circuit 1. In order to suppress this current, in this embodiment, the Schottky barrier diode SBD is connected in parallel with the capacitor C21, the anode of the Schottky barrier diode SBD and one end of the capacitor C21 are provided on the common potential side, and the cathode of the Schottky barrier diode SBD. The other end of the capacitor C21 is connected to one end of the secondary winding Nc of the transformer T1 via a resistor R21. The Schottky barrier diode SBD is an optional component in the present invention.

  The positive input terminal of the comparator 21 is connected to one end of the secondary winding Nc of the transformer T1 via the capacitor C21 and the resistor R21, and the negative input terminal of the comparator 21 is connected to the constant voltage source E21. The output terminal of the comparator 21 is connected to the gate of the switching element Q2, and the drain of the switching element Q2 is connected to the positive input terminal of the comparator 16.

  The comparator 21 charges and discharges the capacitor C21 from the voltage generated in the secondary winding Nc of the transformer T1 according to a time constant determined by the resistor R21 and the capacitor C21 to generate a triangular wave signal. The triangular wave signal and the constant voltage source E21 generate the triangular wave signal. Is compared with the reference signal to be output from the comparator 21 to the gate terminal of the switching element Q2 so that the switching element Q2 is turned on when the peak value of the triangular wave signal is equal to or higher than the set value. 1 is forced to zero, the comparator 16 outputs a high signal, and before the primary winding current becomes zero, the main switching element Q1 is turned on to operate in the continuous current mode.

  Next, the operation of the switching power supply will be described. First, when the main switching element Q1 is on, the alternating current input from the input terminal ACinput is rectified by the diode bridge DB1, and the rectified direct current is the resistance R1, the primary winding Np of the transformer T1, the main switching Electromagnetic energy is accumulated in the primary winding Np through the element Q1 and the resistor R7.

  Next, the main switching element Q1 is turned off, the electromagnetic energy accumulated in the primary winding Np is released, a current flows through the diode D1 and the capacitor C13, and the capacitor C13 is boosted and charged. Thereby, a DC output voltage having a value higher than the AC voltage input from the input terminal ACinput is output from both ends of the capacitor C13 at the output terminal Output. Then, control is performed in which the current (inductor current) flowing through the primary winding Np gradually decreases and returns to zero.

  Next, an outline of the operation of the control circuit 1 will be described. FIG. 2 shows an operation waveform diagram according to this embodiment. First, assume that the main switching element Q1 is turned on. At the input terminal A, a voltage MULT that is a voltage obtained by dividing the DC voltage output from the diode bridge DB1 by the resistors R2 and R3 is input. At the input terminal D, the DC voltage at the output terminal Output is divided by the resistors R8 and R9. A voltage MO, which is a compressed voltage, is input and compared with the output voltage of the constant voltage source E17 in the amplifier 17, and the output voltage of the amplifier 17 and the voltage MULT are multiplied by the multiplier 13 to generate a reference signal of the AC input current. Is done. Then, the comparator 12 compares the voltage of the reference signal with the detection voltage of the resistor R7. At this time, if the detection voltage of the resistor R7 is larger than the reference voltage, the comparator 12 outputs a high level signal to the input terminal R of the RS flip-flop 15, and outputs a low level signal from the output terminal Q of the RS flip-flop 15. The main switching element Q1 is turned off via the driver 11.

  As described above, when the main switching element Q1 changes from the on state to the off state, the following voltage is generated in the resistor R7. That is, a difference voltage between the Vds of the main switching element Q1 and the ground potential is generated. Accordingly, a similar voltage is generated in the primary winding Np, and a voltage is also generated in the secondary winding Nc in proportion to the winding ratio. The voltage is generated at the input terminal B of the control circuit 1 via the resistor R4. , Observed as a ZCD (zero / current) signal.

  With the above operation, the secondary winding Nc can detect in the control circuit 1 that the current flowing through the primary winding Np becomes zero during the OFF period of the main switching element Q1. Here, when the current flowing through the primary winding Np becomes zero, the voltage of the secondary winding Nc becomes negative, the ZCD signal becomes low level, and the voltage of the ZCD signal becomes smaller than the output voltage of the constant voltage source E16. The comparator 16 outputs a low level signal to the OSMV 19, the OSMV 19 emits a prescribed high level signal, outputs it to the input terminal S of the RS flip-flop 15, and outputs a high level signal from the output terminal Q of the RS flip-flop 15. A signal is output (set), and the main switching element Q1 is turned on via the driver 11. With the above operation, the control circuit 1 performs on / off control of the main switching element Q1.

  Next, details of the operation of the control circuit 1 will be described. First, a case where the control circuit 1 performs on / off control of the main switching element Q1 at a constant period will be described. When the capacitor input type power supply is used instead of the control circuit 1, the current flowing at the input terminal ACinput is a pulsed current that changes sharply.

  Here, since the electric power is a product of the voltage and the current, a region where the electric power that is the product of the voltage and the current becomes zero is widened in time, and it is difficult to efficiently extract the electric power. In addition, since the current waveform changes sharply, electrical noise is generated, which adversely affects the operation of other devices.

  Therefore, a primary winding current INp that satisfies the following conditions is passed through the primary winding Np. That is, the envelope Evr1 formed by the peak value of the primary winding current INp, in other words, the current flowing at the input terminal ACinput has the same waveform as the voltage applied at the input terminal ACinput.

  Specifically, in order to pass the primary winding current INp as described above to the primary winding Np, the following operation is performed. That is, in the region where the primary winding current INp has a slope that rises to the right, the main switching element Q1 is turned on and the primary winding current INp increases, and the primary winding current INp falls to the right. In the region having the slope of, the primary winding current INp is decreasing due to the off period of the main switching element Q1. Therefore, the peak value of the primary winding current INp is adjusted by adjusting the time length for turning on the main switching element Q1.

  Here, a signal (on trigger) for turning on the main switching element Q1 is detected by the secondary winding Nc and is generated based on the ZCD signal input at the input terminal B. On the other hand, a signal (off trigger) for turning off the main switching element Q1 is a voltage proportional to the voltage MULT inputted at the input terminal A, the voltage MO inputted at the input terminal D, and the switching current IQ1 flowing through the main switching element Q1. Generated based on CS. These on-trigger and off-trigger are output from the output terminal E as the voltage VGS. With the above operation, the control circuit 1 turns on / off the main switching element Q1 while improving the power factor, and reduces the influence on the surrounding electrical devices.

  Next, the operation of the continuous current mode operation circuit 2 will be described. In the continuous current mode operation circuit 2, the capacitor C <b> 21 charges and discharges from the voltage generated in the secondary winding Nc of the transformer T <b> 1 to generate a triangular wave signal, and outputs it to the positive input terminal of the comparator 21. The comparator 21 compares this triangular wave signal with a reference signal generated by the voltage of the constant voltage source E21. When the peak value of the triangular wave signal becomes equal to or higher than a set value, the comparator 21 outputs a high signal to the gate terminal of the switching element Q2. Output. Thereby, the switching element Q2 is turned on.

  When the switching element Q2 is turned on, the voltage at the ZCD terminal is inverted to change from high to low and output to the positive input of the comparator 16. When the low ZCD signal is output to the comparator 16, a high signal for a predetermined time is output from the OSMV 19. The OSMV 19 outputs this signal to the set terminal S of the RS flip-flop 15.

  The RS flip-flop 15 performs a set operation. Based on the voltage at the output terminal Q of the RS flip-flop 15, the driver 11 turns the main switching element Q <b> 1 on and off at a frequency (switching frequency) higher than the frequency of the alternating current input to the switching power supply 1. In this case, the driver 11 inputs a high-level signal by turning on the switching element Q2 before the current of the primary winding becomes zero and setting the ZCD terminal to low, so that the main switching element Q1 has the primary winding. Turns on before the line current becomes zero. As a result, as shown in FIG. 2, the current of the primary winding Np becomes a continuous current operation, and the main circuit of the power factor correction circuit can be operated in the continuous current mode.

  On the other hand, when the peak value of the triangular wave signal becomes equal to or less than the set value, it is output as a low signal to the gate terminal of the switching element Q2. Thereby, the switching element Q2 is turned off. When the switching element Q2 is turned off, the comparator 16 compares the voltage input from the input terminal B with the comparison result of the output voltage of the constant voltage source E16 and outputs the comparison result to the OSMV 19. The OSMV 19 outputs a low level signal to the set terminal S of the RS flip-flop 15 when a signal that maintains a certain level or a signal that rises from a low level to a high level is input, but a signal that falls from a high level to a low level. When input, a signal (pulse) that is at a low level before the falling of the signal, becomes a high level for a certain time in synchronization with the rising, and then returns to a low level is output to the set terminal S of the RS flip-flop 15 To do.

  Based on the voltage input to the reset terminal R or the set terminal S, the RS flip-flop 15 outputs a high signal during the set operation and a low signal during the reset operation. The driver 11 is composed of a switching circuit using a transistor, for example, and at a frequency (switching frequency) higher than the frequency of the alternating current input to the switching power supply 1 based on the voltage at the output terminal Q of the RS flip-flop 15. The main switching element Q1 is turned on / off. The driver 11 turns on the main switching element Q1 when a high level signal is inputted, and turns off the main switching element Q1 when a low level signal is inputted. As a result, the main circuit of the power factor correction circuit which was in the current continuous mode returns to the current critical mode.

  From the above operations, in this embodiment, by operating in the current critical mode at light load and in the current continuous mode at heavy load, it is possible to take advantage of each mode and to take measures against subharmonics. No slope compensation is required. Further, from the above, for example, even when the input / output voltage difference is small, such as a 200 V system input, the positive voltage of the secondary winding Nc is small, the negative voltage is large, and the level of the triangular wave signal is lowered. Therefore, it becomes difficult to enter the current continuous mode, and it is possible to operate in the current critical mode with little switching loss.

  Next, FIG. 3 shows an embodiment in which the main part of the power factor correction circuit according to the present invention is integrated. The same components as those in the above embodiment are given the same numbers in FIG. 3 as in FIG.

  The control circuit 1 according to the embodiment shown in FIG. 3 includes a driver 11, a comparator 12 (switching element current detecting means), a multiplier 13, an RS flip-flop 15, and a comparator 16 (zero) as in the above-described embodiment. Current detection means), an amplifier 17 (output voltage detection means), a comparator 18 (frequency setting means), and constant voltage sources E16 and E18, which are based on various signals input at input terminals A to D. A voltage VGS for turning on / off the switching element Q1 is generated, and output operation is performed from the output terminal E.

  In this embodiment, an OR circuit 14 is provided. The OR circuit 14 is connected to the output of the comparator 16 and the output of the comparator 18, and the OR circuit 14 emits a prescribed high-level signal and the input terminal S of the RS flip-flop 15. And a high level signal is output (set) from the output terminal Q of the RS flip-flop 15, and the main switching element Q 1 is turned on via the driver 11.

  On the other hand, the continuous current mode operation circuit 2 according to this embodiment includes a comparator 18, a constant voltage source E18, an OR circuit 14, a Schottky barrier diode SBD, a capacitor C21, and a resistor R21. The comparator 18, the constant voltage source E18, and the OR circuit 14 are included in the control circuit 1.

  Similar to the above embodiment, the triangular wave signal is generated from the secondary winding Nc by the charge / discharge operation of the capacitor C21, and this triangular wave signal is output from the input terminal A of the control circuit 1 to the positive input terminal of the comparator 18. The comparator 18 plays the same role as the comparator 21 of the above-described embodiment, and the triangular wave signal generated by the continuous current mode operation circuit 2 and the reference signal generated by the constant voltage source E18 are compared by the comparator 18 to obtain the triangular wave signal. An ON signal is output from the comparator 18 to the OR circuit 14 when the peak value of becomes higher than the set value.

  Next, the operation of the continuous current mode operation circuit 2 will be described. In the continuous current mode operation circuit 2, the capacitor C21 charges and discharges from the voltage generated in the secondary winding Nc of the transformer T1, generates a triangular wave signal, and outputs it to the positive input terminal of the comparator 18. The comparator 18 compares this triangular wave signal with a reference signal generated by the voltage of the constant voltage source E18. When the peak value of this triangular wave signal becomes equal to or higher than a set value, the comparator 18 outputs a high signal to the input terminal of the OR circuit 14. The OR circuit 14 outputs this signal to the set terminal S of the RS flip-flop 15, and the main choke current is in continuous current operation as in the previous embodiment, and the main circuit of the power factor correction circuit is in the continuous current mode. It can be operated.

  On the other hand, when the peak value of this triangular wave signal becomes equal to or less than the set value, it is output as a low signal to the input terminal of the OR circuit 14. The OR circuit 14 does not output a signal even when this signal is received. On the other hand, the OR circuit 14 outputs a signal to the RS flip-flop 15 according to the signal output from the comparator 16, and the RS flip-flop 15 outputs the output terminal based on the voltage input to the reset terminal R or the set terminal S. Q outputs a high signal during the set operation and a low signal during the reset operation. Based on the voltage at the output terminal Q of the RS flip-flop 15, the main switching element Q1 is turned on / off at a frequency (switching frequency) higher than the frequency of the alternating current input to the switching power supply 1. The driver 11 turns on the main switching element Q1 when a high level signal is inputted, and turns off the main switching element Q1 when a low level signal is inputted. As a result, the main circuit of the power factor correction circuit which was in the current continuous mode returns to the current critical mode.

  From the above operation, in this embodiment as well, in the same way as in the previous embodiment, the operation in the current critical mode at the time of light load and the current continuous mode at the time of heavy load can be utilized to take advantage of each mode. At the same time, slope compensation for sub-harmonic countermeasures is not required. Further, from the above, for example, even when the input / output voltage difference is small, such as a 200 V system input, the positive voltage of the secondary winding Nc is small, the negative voltage is large, and the level of the triangular wave signal is lowered. The current continuous mode is less likely to be achieved and the current critical mode can be smoothly operated.

  Although the control circuit 1 according to the embodiment of the present invention is assumed to be configured by one module or one integrated circuit, the present invention is not limited to the embodiment.

  According to the present invention, the triangular wave signal is generated from the voltage generated in the secondary winding of the transformer having the magnetically coupled primary and secondary windings, and the peak value of the triangular wave signal is equal to or higher than the set value. When the main switching element is off, the output current becomes zero. By providing mode operation means, it is possible to take advantage of each mode by operating in current critical mode at light load and continuous current mode at heavy load, and for sub-harmonic measures. Slope compensation is unnecessary, and the circuit can be simplified, so that it can be used industrially.

  Further, according to the present invention, for example, even when the input / output voltage difference is small, such as a 200V system input, the positive voltage of the secondary winding is small, the negative voltage is large, and the level of the triangular wave signal is increased. Therefore, the current continuous mode becomes difficult to operate, and since it can operate smoothly in the current critical mode, it can be used industrially.

It is the circuit diagram which showed one Example of the power factor improvement circuit which concerns on this invention. It is an operation | movement waveform diagram in the circuit shown in FIG. It is the circuit diagram which showed the Example at the time of integrating the principal part of the power factor improvement circuit based on this invention into an integrated circuit.

Explanation of symbols

T1 transformer Np transformer T1 primary winding Nc transformer T1 secondary winding Q1 main switching element Q2 switching element D1 rectifier diode DB1 diode bridge R1, R5, R6, R7, R8, R9, R10, R21 resistor C1 input capacitor C13 Smoothing capacitors E16, E17, E18, E21 Constant voltage source C21 Time constant capacitor SBD Schottky barrier diode 1 Control circuit 2 Continuous current mode operation circuit 11 Driver 12 Comparator (switching element current detection means)
13 multiplier 14 OR circuit 15 RS flip-flop 16 comparator (zero current detection means)
17 Amplifier (Output voltage detection means)
18 Comparator (frequency setting means)
19 One-shot multivibrator (OSMV)
21 Comparator

Claims (4)

Rectifying means for rectifying and supplying AC voltage, a primary winding and a secondary winding, one end of the primary winding being connected to the rectifying means, and the other end of the primary winding of the transformer Power factor improvement for controlling the output voltage of the rectifying means by being repeatedly turned on and off at a cycle faster than the cycle of the AC voltage by the main switching device. A circuit,
Zero current detecting means connected to the secondary winding, detecting that the main switching element is turned off, and detecting that the primary winding current is zero during the off period of the main switching element;
A triangular wave signal is generated from a voltage generated in the secondary winding, and when the peak value of the triangular wave signal exceeds a set value, the detection result of the zero current detecting means is ignored and the main switching element is forcibly A continuous current mode operation means for operating in a continuous current mode by turning on
A power factor correction circuit characterized by comprising: The continuous current mode operation means includes a switching element, generates a triangular wave signal from a voltage generated in the secondary winding, and turns on the switching element when a peak value of the triangular wave signal exceeds a set value. The power factor correction circuit according to claim 1, wherein the main switching element is forcibly turned on. The continuous current mode operation means includes an OR circuit, generates a triangular wave signal from a voltage generated in the secondary winding, and outputs the triangular wave signal from the OR circuit when a peak value of the triangular wave signal becomes a set value or more. 2. The power factor correction circuit according to claim 1, wherein an on signal is forcibly oscillated to the switching element to turn on the main switching element. 4. The continuous current mode operation means includes a capacitor, and is configured to generate a triangular wave signal by charging and discharging based on a voltage generated in the secondary winding. Power factor correction circuit.

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