JP4279937B2 - Power factor correction circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power factor correction circuit for a switching power supply that obtains an output voltage having substantially the same potential from an AC 100V / 200V power supply.
[0002]
[Prior art]
FIG. 6 shows the configuration of a power factor correction circuit for a switching power supply disclosed in Japanese Patent Laid-Open No. 7-194124 as a first conventional example. As shown in the figure, the power factor correction circuit of this example includes a low-pass filter LF, a boosting inductor L1, a rectifier bridge D1, diodes D7 and D8, a boosting switching element MOS FET (hereinafter simply referred to as a switching element). Q4, Q5, boosting output capacitors C1, C2, a transformer T4, and a changeover switch SW1. The changeover switch SW1 is a switch for switching between AC100V / AC200V.
[0003]
The operation of the power factor correction circuit when AC 100 V is input will be described. When the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N and the switching element Q4 is turned on, the input current is the active line side L → inductor L1 → rectifier bridge D1 → switching element Q4 → When the switching element Q4 is turned off and the switching element Q4 is turned off, the input current flows from the active line L → inductor L1 → rectifier bridge D1 → diode D7 → output capacitor C1 → switch SW1 → It flows along the route from the transformer T4 to the neutral wire side N.
[0004]
Further, when the voltage on the neutral line side N is higher than the voltage on the active line side L and the switching element Q5 is turned on, the input current is neutral line side N → transformer T4 → switching switch SW1 → switching element Q5 → rectifier. When the switching element Q5 is turned off and the switching element Q5 is turned off, the input current flows through the path of the bridge D1 → inductor L1 → active line side L. It flows through the path of L1 → active line side L.
[0005]
Next, the operation at the time of AC200V input will be described. When the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N and the switching element Q4 is turned on, the input current is the active line side L → inductor L1 → rectifier bridge D1 → switching element Q4 → When switching element Q5 → rectifier bridge D1 → transformer T4 → neutral line side N flows and switching element Q4 is turned off, the input current is L → active line side L1 → rectifier bridge D1 → diode D7 → output capacitor C1 → It flows through the path of the output capacitor C2, the diode D8, the rectification bridge D1, the transformer T4, and the neutral line side N.
[0006]
When the voltage on the neutral line side N is higher than the voltage on the active line side L and the switching element Q5 is turned on, the input current is neutral line side N → transformer T4 → rectifier bridge D1 → switching element Q4 → switching. When the element Q5 → rectifier bridge D1 → inductor L1 → active line side L flows and the switching element Q5 is turned off, the input current is neutral line side N → transformer T4 → rectifier bridge D1 → diode D7 → output capacitor C1 → It flows through the path of the output capacitor C2, the diode D8, the rectification bridge D1, the inductor L1, and the active line side L.
[0007]
The power factor correction circuit includes a control circuit 7 that performs switching control of the switching elements Q4 and Q5. The control circuit 7 converts the induced voltage of the secondary winding of the transformer T4, in which the primary winding is inserted on the neutral line between the low-pass filter LF and the rectifier bridge D1, to the choke of the boosting inductor L1. Monitor as current detection signal. Based on this detection signal, the control circuit 7 turns on / off the switching elements Q4 and Q5 so that the series voltage between the output capacitors C1 and C2 is constant and the input current waveform is a sine wave. Control the width.
[0008]
Reference numeral 1 denotes a first DC / DC converter corresponding to the load of the power factor correction circuit, and performs constant voltage control independently by an internal control circuit.
[0009]
Next, a power factor correction circuit disclosed in Japanese Patent Laid-Open No. 7-298611 will be described as a second conventional example with reference to FIG.
[0010]
As shown in the figure, this power factor correction circuit includes a rectifier bridge D1, step-up switching inductors L4 and L5, control windings 50 and 51, a primary winding 52, a secondary winding 53, and a tertiary winding. 54, a transformer D5, a diode D9, a rectifying and smoothing circuit 9 including diodes D10 and D11, an inductor L2, and an output capacitor C5, and a boosting switching element MOS FET (hereinafter simply referred to as a switching element) Q6. , Smoothing capacitors C1 and C2 and a changeover switch SW2. Switching of AC100V / AC200V is performed by the changeover switch SW2. Further, 11 is a control circuit for controlling the switching element Q6, and 10 is a load.
[0011]
Next, the operation of the power factor correction circuit when AC 100 V is input will be described. When the switching element Q6 is on and the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N, the input current is the active line side L → rectifier bridge D1 → step-up switching inductor L4. → Control winding 50 → Smoothing capacitor C1 → Changeover switch SW2 → Neutral line N When the voltage on the neutral line side N is higher than the voltage on the active line side L, the input current is neutral line N → selection switch SW2 → smoothing capacitor C2 → control winding 51 → step-up switching inductor L5 → rectifier bridge. It flows along the route of D1 → active line side L.
[0012]
At the time of AC200V input, when the switching element Q6 is on and the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N, the input current is the active line side L → rectifier bridge D1 → boost Switching inductor L4 → control winding 50 → smoothing capacitor C1 → smoothing capacitor C2 → control winding 51 → step-up switching inductor L5 → rectifier bridge D1 → neutral line side N path, neutral line side N Is higher than the voltage on the active line side L, the input current is neutral side N → rectifier bridge D1 → step-up switching inductor L4 → control winding 50 → smoothing capacitor C1 → smoothing capacitor C2 → control winding. The current flows through a path 51 → step-up switching inductor L5 → rectifier bridge D1 → active line side L.
[0013]
When switching element Q6 is turned on, the voltage at point I of control winding 50 of transformer T5 is lower than the voltage at point J, while the voltage at point K of control winding 51 of transformer T5 is lower than the voltage at point L. Also gets higher. Therefore, boosting operation of inductors L4 and L5 is performed in the same manner as when switching elements Q4 and Q5 of the conventional circuit shown in FIG. 6 are turned on.
[0014]
[Problems to be solved by the invention]
However, the power factor correction circuit shown in FIG. 6 has a problem that the circuit configuration is complicated as a whole, such as requiring two switching elements Q4 and Q5. In contrast, the circuit shown in FIG. 7 has a relatively simple configuration, but has a problem that the voltages of the input capacitors C1 and C2 are likely to fluctuate greatly at light loads.
[0015]
The present invention solves such a problem, and can simplify the circuit configuration and can make the voltage of the input capacitor constant regardless of the load current. It is to provide a rate improvement circuit.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 includes a rectifier bridge connected to an AC power supply, an inductor connected to one end on the output side of the rectifier bridge, and a load at one end of the inductor. for A transformer having one winding connected in series, another winding connected in parallel to the load at one end of the one winding, and the load at one end of one winding of the transformer Against A capacitor connected in parallel; Above Input from rectifier bridge Voltage Means for detecting and said detection Comparing means for comparing the input voltage detected by the means for comparing with a reference voltage; The capacitor voltage is the input To voltage Almost proportional , Switching the switching element based on the comparison result of the comparison means, Control means for controlling an AC voltage applied to the other winding of the transformer.
[0017]
According to a second aspect of the present invention, there is provided a rectifier bridge connected to an AC power source and one end on the output side of the rectifier bridge. Parallel to each other Followed by boosting Volume 1 and 2 An inductor having a line and the inductor A third winding connected in series to the load at one end of the first winding, and a fourth winding connected in series to the load at one end of the second winding of the inductor A transformer having a fifth winding connected in parallel to the load at one end of the third winding, and a third of the transformer A first capacitor and a second capacitor connected in parallel to the winding and across the first midpoint; Above From the rectifier bridge Input voltage on the positive or negative side Detecting means for detecting, and the input detected by the detecting means A first comparison unit that compares a voltage on the positive side of the voltage with a reference voltage; a second comparison unit that compares a voltage on the negative side of the input voltage detected by the detection unit with a reference voltage; The second The voltage of the capacitor is the input To voltage Almost proportional , Switching the switching element based on the comparison result of the first and second comparison means, Of trance 5th And a control means for controlling an AC voltage applied to the winding.
[0018]
As described above, according to the first and second aspects of the present invention, the voltage of the capacitor applied to both ends of one winding and the current flowing through the inductor are controlled by controlling the AC voltage applied to the other winding of the transformer. Since the capacitor voltage is made substantially proportional to the input current, the circuit configuration can be simplified and the input capacitor voltage can be made constant regardless of the load current.
[0020]
Claim Three The invention provides another winding of the transformer Or directly to the fifth winding Connected to the column With one end Second inductor And the control means turns on or off the switching element. More control the magnetic flux of the second inductor, the other winding of the transformer Or on the fifth winding It is characterized in that an AC voltage to be applied is obtained.
[0021]
Claim Four The invention is characterized in that an inductance leaking from another winding of the transformer is used as the inductor for boosting.
[0022]
That is, according to the present invention, if the leakage inductance of the transformer is used as a boost inductor, the number of parts can be reduced and the circuit configuration can be simplified.
[0024]
According to this invention, the control means for generating the control signal can be realized with a relatively simple circuit configuration.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0026]
FIG. 1 shows a configuration of a power factor correction circuit according to the first embodiment of the present invention.
[0027]
As shown in the figure, this power factor correction circuit includes a rectifier bridge D1, a boosting inductor L1, a transformer T2 including windings n1, n2, and nr, a switching element SW1, an input capacitor C1, a diode D3, and a switching element SW1. It is comprised from the control part 2 which performs switching control. The control unit 2 includes a diode D2, resistors R1 to R4, a capacitor C3, comparators CMP1 and CMP2, and a triangular wave generator 20.
[0028]
Reference numeral 1 denotes a DC / DC converter corresponding to a load of the power factor correction circuit, and constant voltage control is performed independently of the power factor correction circuit by an internal control circuit. In this power factor correction circuit, there is no switch for switching the input power supply, and either one of the commercial AC power supply 100V or 200V is used.
[0029]
Next, the operation of the power factor correction circuit of this embodiment will be described.
[0030]
First, a process of generating a signal for switching the switching element SW1 will be described. The peak value Vp of the input voltage from the commercial AC power supply is detected by the diode D2, the resistors R1 and R2, and the capacitor C3. The detected peak value Vp is compared with the reference voltage value generated by dividing the terminal voltage Vc of the capacitor C3 by the resistors R3 and R4 by the comparator CMP1, and the error signal as the comparison result is the comparator CMP2. Is compared with the triangular wave generated by the triangular wave generator 20. This comparison result is generated as an on / off signal supplied to the switching element SW1. By switching the switching element SW1 based on the on / off signal generated in this way, the terminal voltage Vc of the input capacitor C1 is controlled to be proportional to the peak value Vp of the input voltage of the commercial AC power supply.
[0031]
Next, the principle that the power factor is improved by the switching control of the switching element SW1 will be described. Note that n1, n2, and nr represent the number of turns of each winding.
[0032]
When the switching element SW1 is turned on, the terminal voltage Vc of the input capacitor C1 is applied to the winding n1 of the transformer T2, and a voltage of Vc × n2 / n1 is generated in the winding n2 of the transformer T2. The relationship between the voltage at point A and the voltage at point B at both ends of the winding n2 is point A <point B, and the current IL flowing through the boosting inductor L1 increases. Therefore, if the input voltage of the commercial AC power supply is higher than Vc × (1−n2 / n1), the input current flows, and the power factor improvement effect is obtained.
[0033]
On the other hand, when the switching element SW1 is turned off, the terminal voltage Vc of the input capacitor C1 is applied to the winding nr of the transformer T2, and a negative voltage of −Vc × n2 / nr is generated in the winding n2 of the transformer T2. Therefore, the voltage at the point A becomes higher than the voltage at the point B, and the current IL flowing through the boosting inductor L1 decreases.
[0034]
Therefore, according to the power factor correction circuit of the present embodiment, the circuit configuration can be simplified, and the voltage generated in the input capacitor C1 can be made constant without being affected by the load current of the DC / DC converter 1. Further, if the leakage inductance of the transformer T2 is used as the step-up inductor L1, the number of parts can be further reduced.
[0035]
Next, another embodiment of the present invention will be described.
[0036]
FIG. 2 shows a configuration of a power factor correction circuit according to the second embodiment of the present invention.
[0037]
As shown in the figure, the power factor correction circuit includes a rectifier bridge D1, a boosting inductor L1, a transformer T2 having turns n1 and n2, an input capacitor C1, diodes D4 and D5, a supersaturated inductor Lm, and the supersaturated inductor Lm. It is comprised from the control part 3 which controls the voltage applied to. The control unit 3 includes a diode D2, resistors R1 to R4, a capacitor C3, a comparator CMP3, and a transistor Q1.
[0038]
Reference numeral 4 denotes a DC / DC converter corresponding to the load of the power factor correction circuit, which performs constant voltage control by varying the on / off time of the switching element SW by an internal control circuit. Note that the power factor correction circuit of this embodiment does not have a changeover switch for commercial AC power supply 100V / 200V.
[0039]
Next, the operation of the power factor correction circuit of this embodiment will be described.
[0040]
First, the peak value Vp of the input voltage of the commercial AC power supply is detected by the diode D2, the resistors R1 and R2, and the capacitor C3. The detected peak value Vp is compared by a comparator CMP3 with a reference voltage value generated by dividing the terminal voltage Vc of the capacitor C3 by resistors R3 and R4. The error signal obtained as a result of this comparison is amplified by the transistor Q1 and applied as a control voltage to the control winding of the supersaturated inductor Lm.
[0041]
Here, the control unit 3 controls the time for applying the control voltage to the auxiliary winding of the supersaturated inductor Lm so that the terminal voltage Vc of the input capacitor C1 is substantially proportional to the peak value Vp of the input voltage of the commercial AC power supply. By such control, the terminal voltage Vc of the input capacitor C1 can be made constant without being affected by the load current of the DC / DC converter 4.
[0042]
Next, the operation of this power factor correction circuit will be described with reference to FIG.
[0043]
When the commercial AC power supply is applied to the rectifying bridge D1, charges are accumulated in the input capacitor C1, and a voltage is generated between the terminals of the input capacitor C1. When the switching element SW in the DC / DC converter 4 is turned on (FIG. 5 (A) VSW), −Vc × na / n is applied to the auxiliary winding na of the transformer T1 (where na and n are the windings na and n). Negative number of turns). During the period Tm when the switching element SW is on, the voltage generated in the auxiliary winding na of the transformer T1 is applied to both ends of the supersaturated inductor Lm (FIG. 5 (B) Vm). After the on-period Tm of the switching element SW elapses, the supersaturated inductor Lm is saturated, a negative voltage of −Vc × na / n is generated in the winding n1 of the transformer T2, and Vc × n2 is applied to the winding n2 of the transformer T2. / N1 voltage is generated (FIG. 5C, VT2), and the voltage applied to the boosting inductor L1 drops (FIG. 5D) VL. As a result, the voltage at the point C in FIG. 2 becomes lower than the voltage at the point D, and the current IL flowing through the boosting inductor L1 increases (FIG. 5 (E) IL: tLon). Therefore, if the input voltage from the commercial AC power source is higher than Vc × (1-n2 / n1), the input current IL of the commercial AC power source flows, and the power factor improvement effect is obtained.
[0044]
Subsequently, when the switching element SW in the DC / DC converter 4 is turned off (VSW in FIG. 5A), the diode D2 of the control unit 3 is turned on, and the terminal voltage Vc of the input capacitor C1 is applied to the winding n1 of the transformer T2. The negative voltage of −Vc × n2 / n1 is generated in the winding n2 of the transformer T2 (FIG. 5 (C) VT2). Accordingly, the voltage at the point C in FIG. 2 becomes higher than the voltage at the point D, and the current flowing through the boosting inductor L1 decreases (FIG. 5 (E) IL: tLoff).
[0045]
If the leakage inductance of the transformer T2 is used as the boosting inductor L1, the number of parts can be reduced and the circuit configuration can be simplified.
[0046]
FIG. 3 shows the configuration of the power factor correction circuit according to the third embodiment of the present invention.
[0047]
As shown in the figure, this power factor correction circuit includes a rectifier bridge D1, a boosting inductor L3 composed of windings nL1 and nL2, a transformer T3 composed of windings n1, n2, n3 and nr, a switching element SW1, and an input capacitor. C1, C2, a diode D3, a changeover switch C-SW, and a control unit 5 that controls switching of the switching element SW1. The changeover switch C-SW is a switch for switching between commercial AC power supplies 100V / 200V.
[0048]
The controller 5 includes diodes D2 and D6, resistors R1 to R8, capacitors C3 and C4, comparators CMP4 to CMP6, transistors Q2 and Q3, a photocoupler PC1, and a triangular wave generator 20. Reference numeral 1 denotes a DC / DC converter corresponding to the load of the power factor correction circuit, and the constant voltage control is independently performed on the power factor correction circuit by an internal control circuit.
[0049]
Next, the operation of this power factor correction circuit will be described.
[0050]
First, a process of generating an on / off signal for switching the switching element SW1 will be described.
[0051]
The peak value Vp on the positive side of the input voltage of the commercial AC power supply is detected by a diode D2, resistors R1, R2, and a capacitor C3, and the peak value Vp on the negative side is detected by a diode D6, resistors R5, R6, and a capacitor C4. The The detected positive-side peak value Vp is compared with a reference voltage value generated by dividing the terminal voltage of the input capacitor C1 by resistors R3 and R4 in the comparator CMP4, while the detected negative-side peak value Vp is detected. The value Vp is compared in the comparator CMP5 with a reference voltage value generated by dividing the terminal voltage of the input capacitor C2 by the resistors R7 and R8. The error signals, which are the comparison results obtained by the comparators CMP4 and CMP5, are inverted and wired-ORed by the transistors Q2 and Q3, respectively.
[0052]
The photodiode of the photocoupler PC1 is driven by the wired-or signal, and the output signal of the phototransistor and the triangular wave generated by the triangular wave generator 20 are compared by the comparator CMP6. An error signal obtained as a result of this comparison is supplied to the switching element SW1 as an on / off signal. That is, in the present embodiment, by varying the on / off width of the on / off signal supplied to the switching element SW1, the terminal voltages of the input capacitors C1 and C2 are respectively the positive and negative peak values Vp of the commercial AC power supply. Is controlled to be approximately proportional to Thereby, the terminal voltage of each of the input capacitors C1 and C2 can be kept constant without being influenced by the load current of the DC / DC converter 1.
[0053]
Next, the operation when inputting AC 100 V by shorting the changeover switch C-SW will be described.
[0054]
When the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N, the input current flows in the order of the neutral line side L → the diode D1 → the winding nL1 of the transformer T3 → the winding n2 of the transformer T3. To charge the input capacitor C1. Furthermore, the electric charge accumulated in the input capacitor C1 becomes a current and returns to the neutral line side N through the changeover switch C-SW1. Further, when the voltage on the neutral line side N is higher than the voltage on the active line side L, the input current flows through the neutral line side N → the changeover switch C-SW1, whereby the input capacitor C2 is charged and accumulated in the input capacitor C2. The generated electric charge is discharged as a current that flows in the order of the winding n3 of the transformer T3 → the winding nL2 of the transformer T3 → the diode D1 → the neutral line side L.
[0055]
Next, a process in which the power factor is improved by controlling the switching element SW1 will be described. Note that n1, n2, n3, and nr represent the number of turns of each winding.
[0056]
When the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N and the switching element SW1 is on, the voltage Vc between the input capacitors C1 and C2 is applied to the winding n1 of the transformer T3. A voltage of Vc × n2 / n1 is induced in the winding n2 of the transformer T3. Therefore, the voltage at the point E becomes lower than the voltage at the point F, and the current flowing through the boosting inductor L3 increases. For this reason, if the input voltage Vi is higher than Vc / 2 × (1−n2 / n1) (where n2 = n3), the input current flows, and the power factor improvement effect is obtained.
[0057]
When the switching element SW1 is turned off, the terminal voltage Vc of the input capacitor C1 is applied to the winding nr of the transformer T3, and a voltage of −Vc × n2 / nr is generated across the winding n2 of the transformer T3. For this reason, the voltage at the point E becomes higher than the voltage at the point F, and the current flowing through the boosting inductor L3 decreases.
[0058]
When the voltage on the neutral line side N of the commercial AC power supply is higher than the voltage on the active line side L and the switching element SW1 is turned on, the voltage Vc between the input capacitors C1 and C2 is applied to the winding n1 of the transformer T3. A voltage of Vc × n3 / n1 is generated in the winding n3 of the transformer T3. Therefore, the voltage at the point G becomes higher than the voltage at the point H, and the current flowing through the boosting inductor L1 increases. For this reason, if the input voltage Vi is higher than Vc / 2 × (1−n2 / n1) (where n2 = n3), the input current flows, and the power factor improvement effect is obtained.
[0059]
When the switching element SW1 is turned off, the terminal voltage Vc of the input capacitor C1 is applied to the winding nr of the transformer T3, and a negative voltage of −Vc × n3 / nr is generated in the winding n3 of the transformer T3. For this reason, the voltage at the point G becomes lower than the voltage at the point H, and the current flowing through the boosting inductor L3 decreases.
[0060]
Subsequently, an operation when AC 200 V is input by opening the changeover switch C-SW will be described.
[0061]
When the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N, the input current is from the active line side L → the diode D1 → the winding nL1 of the boosting inductor L3 → the winding n2 of the transformer T3. The path flows and charges each input capacitor C1 and C2. The electric charge accumulated in each of the input capacitors C1 and C2 is discharged by flowing as a current through a path from winding n3 of transformer T3 → winding nL2 of boosting inductor L3 → diode D1 → neutral side N. .
[0062]
When the voltage on the neutral line side N of the commercial AC power supply is higher than the voltage on the active line side L, the input current is from the neutral line side N → the diode D1 → the winding nL2 of the boosting inductor L3 → the winding of the transformer T3. The input capacitors C1 and C2 are charged through the line n3. The electric charge accumulated in each of the input capacitors C1 and C2 is released by flowing as a current through the path of the winding n2 of the transformer T3 → the winding nL1 of the boosting inductor L3 → the diode D1 → the active line side L.
[0063]
Next, the process by which the power factor is improved by this embodiment will be described.
[0064]
When the switching element SW1 is on, the voltage Vc between the input capacitors C1 and C2 is applied to the winding n1 of the transformer T3, and a voltage of Vc × n2 / n1 is generated in the winding n2 of the transformer T3. A voltage of Vc × n3 / n1 is generated in the winding n3. Therefore, the voltage at the point E becomes lower than the voltage at the point F, the voltage at the point G becomes higher than the voltage at the point H, and the current flowing through the boosting inductor L3 increases. For this reason, if the input voltage Vi is higher than Vc / 2 × (1−n2 / n1) (where n2 = n3), the input current flows, and the power factor improvement effect is obtained. When the switching element SW1 is turned off, the terminal voltage Vc of the input capacitor C1 is applied to the winding nr of the transformer T3, and a voltage of −Vc × n2 / nr is generated in the windings n2 and n3 of the transformer T3. For this reason, the voltage at the point E becomes higher than the voltage at the point F, the voltage at the point G becomes lower than the voltage at the point H, and the current flowing through the boosting inductor L3 decreases.
[0065]
As described above in detail, according to the present embodiment, the alternating current applied to the winding n1 of the transformer T3 is controlled to vary the current flowing through the boosting inductor L3, and the voltages of the capacitors C1 and C2 are used as the input current. Since the circuit is substantially proportional, the circuit configuration can be simplified and the voltages of the input capacitors C1 and C2 can be made constant regardless of the load current.
[0066]
Next, a power factor correction circuit according to a fourth embodiment of the present invention will be described.
[0067]
FIG. 4 shows the configuration of the power factor correction circuit according to the fourth embodiment.
[0068]
As shown in the figure, this power factor improving circuit includes a rectifier bridge D1, a boosting inductor L3 composed of windings L1, nL2, a transformer T3 composed of windings n1, n2, n3, a supersaturated inductor Lm, an input capacitor C1, C2 includes diodes D4 and D5, a changeover switch C-SW, and a control unit 6 that controls the supersaturated inductor Lm. The changeover switch C-SW is a switch for switching commercial AC power supply 100V / 200V. The control unit 6 includes diodes D2 and D6, resistors R1 to R8, capacitors C3 and C4, comparators CMP4 and CMP5, and transistors Q2 and Q3. Reference numeral 4 denotes a DC / DC converter corresponding to the load of the power factor correction circuit, which performs constant voltage control by varying the on / off time of the switching element SW by an internal control circuit.
[0069]
Next, the operation of the power factor correction circuit of this embodiment will be described.
[0070]
The peak value Vp on the positive side of the input voltage of the commercial AC power supply is detected by a diode D2, resistors R1 and R2, and a capacitor C3. The detected peak value Vp of the input voltage is compared with a reference voltage value obtained by dividing the terminal voltage of the input capacitor C1 by resistors R3 and R4 by the comparator CMP4. On the other hand, the peak value Vp of the negative value side peak value Vp of the input voltage is also detected by the diode D6, resistors R5 and R6, and the capacitor C4 in the same way as the positive side, and the detected peak value Vp of the input voltage is the comparator. -At the CMP5, the terminal voltage of the input capacitor C4 is compared with a reference voltage value obtained by dividing by the resistors R7, R8.
[0071]
Two error signals obtained as comparison results from the comparators CMP4 and CMP5 are inverted and wired-ORed by the transistors Q2 and Q3, respectively. The wired-or signal is supplied as a control signal to the auxiliary winding of the supersaturated inductor Lm.
[0072]
Here, the control unit 6 determines the control voltage applied to the auxiliary winding of the supersaturated inductor Lm so that the terminal voltage of each of the input capacitors C1 and C2 is substantially proportional to the peak value Vp of the input voltage from the commercial AC power supply. Control the time. By such control, the terminal voltage of each of the input capacitors C1 and C2 can be made constant without being affected by the load current of the DC / DC converter 4.
[0073]
Subsequently, a process in which the power factor is improved by such control will be described.
[0074]
An operation when AC 100 V is input with the changeover switch C-SW short-circuited will be described.
[0075]
When the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N, and the switching element SW in the DC / DC converter 4 is in the ON state, the auxiliary winding na of the transformer T1 has −Vc × A negative voltage of na / n is generated, and this voltage is applied to the supersaturated inductor Lm. After the ON period of the switching element SW, the supersaturated inductor Lm is saturated, a negative voltage of −Vc × na / n is generated in the winding n1 of the transformer T2, and a voltage of Vc × n2 / n1 is applied to the winding n2 of the transformer T3. Will occur. Therefore, the voltage at the point E becomes lower than the voltage at the point F, and the current flowing through the winding nL1 of the boosting inductor L3 increases. Therefore, when the input voltage of the commercial AC power supply is higher than Vc × (1−n2 / n1) (where n2 = n3), the input current of the commercial AC power supply flows, and a power factor improvement effect is obtained.
[0076]
Thereafter, when the switching element SW is turned off, the diode D2 is turned on, the voltage Vc between the input capacitors C1 and C2 is applied to the winding n1 of the transformer T3, and −Vc × n2 is applied to the winding n2 of the transformer T3. A voltage of / n1 is generated. Therefore, the voltage at the point E becomes higher than the voltage at the point F, and the current flowing through the winding nL2 of the boosting inductor L3 decreases.
[0077]
When the voltage on the neutral line side N of the commercial AC power supply is higher than the voltage on the active line side L and the switching element SW is on, a voltage of Vc × na / n is generated in the auxiliary winding na of the transformer T1. During the ON period of the switching element SW, the voltage is applied to the supersaturated inductor Lm. After the ON period of the switching element SW, the oversaturated inductor Lm is saturated, a voltage of Vc × na / n is generated in the winding n1 of the transformer T3, and a voltage of Vc × n3 / n1 is generated in the winding n3 of the transformer T3. . Therefore, the voltage at the point G becomes higher than the voltage at the point H, and the current flowing through the winding nL2 of the boosting inductor L3 increases. Therefore, when the input voltage of the commercial AC power supply is higher than Vc × (1−n2 / n1) (where n2 = n3), the input current of the commercial AC power supply flows, and a power factor improvement effect is obtained.
[0078]
Thereafter, when the switching element SW is turned off, the diode D2 is turned on, the terminal voltage Vc of the input capacitors C1 and C2 is applied to the winding n1 of the transformer T3, and −Vc × n3 / A voltage n1 is generated. Therefore, the voltage at the point G becomes lower than the voltage at the point H, and the current flowing through the winding nL2 of the boosting inductor L3 decreases.
[0079]
Next, an operation when the changeover switch C-SW is opened and AC 200 V is input will be described.
[0080]
The switching element SW in the DC / DC converter 4 is assumed to be in an off state. When the voltage on the active line side L of the commercial AC power supply is higher than the voltage on the neutral line side N, the input current is the active line side L → rectifier bridge D1 → winding inductor L3 winding nL1 → transformer T3 winding n2 → Input capacitors C1 and C2 → winding n3 of transformer T3 → winding nL2 of boosting inductor L3 → rectifier bridge D1 → neutral side N When the voltage on the neutral line side N is higher than the voltage on the active line side L, the input current is from the neutral line side N → rectifier bridge D1 → winding inductor L3 winding nL2 → transformer T3 winding n3 → input capacitor. The current flows through a path of C2 and C1 → the winding n2 of the transformer T3 → the winding nL1 of the boosting inductor L3 → the rectification bridge D1 → the active line side L.
[0081]
When the switching element SW is turned on, a negative voltage of −Vc × na / n is generated in the auxiliary winding na of the transformer T1. During the ON period of the switching element SW, the voltage is applied to the supersaturated inductor Lm. After the ON period of the switching element SW, the supersaturated inductor Lm is saturated, and a negative voltage of −Vc × na / n is generated in the winding n1 of the transformer T3. A voltage of Vc × n2 / n1 is generated in the winding n2 of the transformer T3, and a negative voltage of −Vc × n3 / n1 is generated in the winding n3 of the transformer T3. Then, the voltage applied to the winding nL1 of the boosting inductor L3 drops, while the voltage applied to the winding nL2 rises.
[0082]
Therefore, the voltage at the point E becomes lower than the voltage at the point F, the voltage at the point G becomes higher than the voltage at the point H, and the current flowing through the boosting inductor L3 increases. For this reason, when the input voltage of the commercial AC power supply is higher than Vc × (1−n2 / n1) (where n2 = n3), the input current flows in, and the power factor improvement effect is obtained.
[0083]
Thereafter, when the switching element SW is turned off, the diode D2 is turned on, the terminal voltage Vc of the input capacitors C1 and C2 is applied to the winding n1 of the transformer T3, and −Vc × n2 / n1 is applied to the winding n2 of the transformer T3. Negative voltage of Vc × n3 / n1 is generated in the winding n3. Then, the voltage applied to the winding nL1 of the boosting inductor L3 increases, while the voltage applied to the winding nL2 decreases. Therefore, the voltage at the point E becomes higher than the voltage at the point F, the voltage at the point G becomes lower than the voltage at the point H, and the current flowing through the boosting inductor L3 decreases.
[0084]
Thus, according to this embodiment, it is possible to provide a power factor correction circuit capable of making the voltages of the input capacitors C1 and C2 constant regardless of the load current.
[0085]
【The invention's effect】
As described above, according to the present invention, by controlling the AC voltage applied to the other winding of the transformer, the voltage of the capacitor applied to both ends of one winding and the current flowing through the inductor are controlled. By making the voltage substantially proportional to the input current, it is possible to provide a power factor correction circuit that can make the terminal voltage of the capacitor constant without being affected by the load current. Moreover, the number of parts can be reduced by using the leakage inductance of the transformer as a boost inductor.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a power factor correction circuit according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram showing a configuration of a power factor correction circuit according to a second embodiment of the present invention.
FIG. 3 is a circuit diagram showing a configuration of a power factor correction circuit according to a third embodiment of the present invention.
FIG. 4 is a circuit diagram showing a configuration of a power factor correction circuit according to a fourth embodiment of the present invention.
5 is a diagram illustrating operation waveforms of respective units in the power factor correction circuit of FIG. 2;
FIG. 6 is a circuit diagram showing a configuration of a conventional power factor correction circuit.
FIG. 7 is a circuit diagram showing a configuration of another conventional power factor correction circuit.
[Explanation of symbols]
LF: Low pass filter
D1 ... Rectifier bridge
L1-L5, Lm ... Inductor
D2-D11 ... Diode
C1 to C5 ... Capacitors
Q1-Q3 ... Transistor
R1 to R11 ... resistance
CMP1 to CMP6 ... Comparator
PC1 ... Photocoupler
A to L: Voltage monitoring points
1,4 ... DC / DC converter
2, 3, 5, 6... Control unit

Claims (4)

A rectifier bridge connected to an AC power source;
An inductor connected to one end of the output side of the rectifier bridge for boosting;
A transformer having one winding connected in series to a load at one end of the inductor, and another winding connected in parallel to the load at one end of the one winding;
A capacitor connected in parallel to the load at one end of one winding of the transformer ;
It means for detecting an input voltage from the rectifier bridge,
Comparing means for comparing the input voltage detected by the detecting means with a reference voltage;
As voltage before Symbol capacitor is substantially proportional to the input voltage, it switches the switching element on the basis of a comparison result of the comparing means, and control means for controlling the AC voltage applied to the other winding of the previous SL trans ,
A power factor correction circuit comprising: A rectifier bridge connected to an AC power source;
An inductor having a are connected in parallel with each other on the output side of the one end of the rectifier bridge, the first, second winding performing boosting,
A third winding connected in series with the load to one end of the first winding of the inductor, and a fourth winding connected in series with the load to one end of the second winding of the inductor. And a transformer having a fifth winding connected in parallel to the load at one end of the third winding;
A first capacitor and a second capacitor connected in parallel to the third winding of the transformer and across the first midpoint;
Detecting means for detecting the positive electrode side or the input voltage of the negative polarity side from the rectifier bridge,
First comparison means for comparing a voltage on the positive side of the input voltage detected by the detection means with a reference voltage;
Second comparison means for comparing a negative side voltage of the input voltage detected by the detection means with a reference voltage;
The first, so that the voltage of the second capacitor is substantially proportional to the input voltage, the first switches the switching device based on the comparison result of the second comparison means, a fifth winding before Symbol trans Control means for controlling the AC voltage applied to the wire;
A power factor correction circuit comprising: Further comprising a second inductor having one end to the other windings or fifth winding of the transformer Ru is connected in series,
Said control means, said controls more magnetic flux of the second inductor to turn on or off the switching element, to obtain an AC voltage applied to the other winding or fifth winding of the transformer The power factor correction circuit according to claim 1, wherein:   2. The power factor correction circuit according to claim 1, wherein an inductance leaking from another winding of the transformer is used as the inductor for boosting.

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