Bridgeless power factor correction circuit

Abstract

A power factor correction circuit without a bridge rectifier. [Solution] A bridgeless power factor correction circuit that improves the power factor of an AC power supply by connecting a first AC power supply, first and second diodes connected in series, first and second capacitors connected in series, inserting a reactor in series between one terminal of the first AC power supply and the connection point of the first and second switch elements, connecting a first bidirectional switch circuit between the connection point of the first and second switch elements and the connection point of the first and second capacitors, and adding a first control circuit that applies an on / off signal to the control electrode of the first bidirectional switch circuit.

Description

Technical Field

[0001] The present invention relates to a switching power supply, and particularly to a bridgeless power factor correction circuit.

Background Art

[0002] As the efficiency of switching power supplies has been improving year by year, the ratio of power loss in the bridge rectifier circuit that converts alternating current to direct current has become high, and circuits for improving this loss have come to be seen frequently. Since a switching circuit called a power factor correction circuit follows the bridge rectifier circuit, a circuit has been devised that makes the power factor correction circuit also serve some functions of the bridge rectifier circuit.

[0003] Among those devises, Patent Documents 1 to 3 shown below have a configuration in which two of the four diodes constituting the bridge rectifier are replaced with switching elements, as shown in the circuit example of FIG. 5.

[0004] Also, in FIG. 5, the reactor for the boost chopper is inserted between the AC power supply and the switching element, and a control circuit is added so that the AC current is made similar to the AC voltage by turning on and off the switching element.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] The circuits provided in Patent Documents 1 to 3 all share the common feature of replacing two of the four diodes that make up the bridge with switching elements. The only difference is the position of the replaced diodes.

[0007] The switching element that replaces the diode acts as either a synchronous rectifier switch or a regular switch, depending on the phase of the AC power supply.

[0008] Therefore, the circuit that generates the signal applied to the control electrode of the switch element becomes complex.

[0009] Therefore, the present invention aims to provide a simple and inexpensive bridgeless power factor correction circuit by enabling the use of the signal from a conventional power factor correction circuit as is for the control electrode of a bidirectional switch circuit that replaces a diode.

[0010] The invention described in claim 1 employs a voltage doubler rectifier circuit, so when the AC voltage is 100V, a DC voltage twice the peak value of 100V AC (141V) is applied to the load. Considering the error in the AC voltage and the voltage boost for power factor correction, a DC voltage of approximately 340V is appropriate.

[0011] When the AC voltage is 200V, applying the invention described in claim 1 results in a set voltage of 680V, ​​which necessitates increasing the voltage rating of the components.

[0012] Therefore, the present invention aims to provide a bridgeless power factor correction circuit that utilizes the fact that a single-phase three-wire AC system consists of two 100V circuits in series, and employs separate voltage doubler rectifier circuits for each 100V, thereby limiting the DC voltage applied to the load to approximately 340V. [Means for solving the problem]

[0013] To achieve the above objective, the invention described in claim 1 is a voltage doubler rectifier circuit in which a first diode and a second diode are connected in series with their orientations aligned, a series circuit consisting of a first capacitor and a second capacitor is connected in parallel to the series circuit consisting of the first diode and the second diode, a load is connected in parallel to the series circuit consisting of the first capacitor and the second capacitor, and a first AC power supply is connected between the connection point of the first diode and the second diode and the connection point of the first capacitor and the second capacitor, thereby converting the AC power of the first AC power supply into DC power and supplying it to the load, wherein a first reactor is inserted in series to one output terminal of the first AC power supply, a first bidirectional switch circuit is connected between the connection point of the first diode and the second diode and the connection point of the first capacitor and the second capacitor, and a first control circuit is added that applies an on / off signal to the control electrode of the first bidirectional switch circuit, thereby improving the power factor of the output current of the first AC power supply.

[0014] The invention described in claim 2 is characterized in that a third diode and a fourth diode are connected in series with their orientations aligned, the series circuit consisting of the third diode and the fourth diode is connected in parallel to the series circuit consisting of the first diode and the second diode, one output terminal of a second AC power supply having the same voltage and phase as the first AC power supply is connected to the output terminal opposite to the output terminal to which the first reactor of the first AC power supply is connected, and the other output terminal is connected to the connection point of the third diode and the fourth diode, a second reactor is inserted in series to the output terminal of the second AC power supply opposite to the output terminal to which the first AC power supply is connected, a second bidirectional switch circuit is connected between the connection point of the third diode and the fourth diode and the connection point of the first capacitor and the second capacitor, and a second control circuit is added that applies an on / off signal to the control electrode of the second bidirectional switch circuit, thereby improving the power factor of the output current of the second AC power supply. [Effects of the Invention]

[0015] According to the invention described in claim 1, the first control circuit can apply a commercially available power factor improvement circuit and is composed of mass-produced and familiar ICs, which reduces the development man-hours and has a great economic effect.

[0016] According to the invention described in claim 2, since DC power is obtained by power factor improvement through voltage doubling rectification from each of the two 100V of a single-phase three-wire AC power supply, it is equivalent to obtaining DC power by full-wave rectifying 200V AC, and the same 340V as in the case of an AC 100V input can be selected as the DC voltage.

Brief Description of the Drawings

[0017] [Figure 1] It is a circuit diagram showing an embodiment of the invention described in claim 1. [Figure 2] It is a circuit diagram showing an embodiment of the invention described in claim 2. [Figure 3] It is a diagram explaining the operation using FIG. 1. [Figure 4] It is a circuit diagram showing an example of means for detecting the output voltage in FIG. 1. [Figure 5] It is a diagram showing an example of a conventional method.

Best Mode for Carrying Out the Invention

[0018] FIG. 1 is a circuit diagram showing an embodiment of the invention described in claim 1. In the figure, 1 and 2 respectively indicate the first diode and the second diode, 3 and 4 respectively indicate the first capacitor and the second capacitor. 5 indicates a load, and 6 indicates the first AC power supply. 8 indicates the first reactor, 9 indicates the first bidirectional switch circuit, and 10 indicates the first control circuit.

[0019] When the first diode 1 conducts and the first capacitor 3 is charged, and the second diode 2 conducts and the second capacitor 4 is charged, a DC voltage twice as high can be obtained at both ends of the series circuit of the two capacitors.

[0020] When the first bidirectional switch circuit 9 repeatedly turns on and off according to the output signal of the first control circuit 10, the current of the first AC power supply 6 passes through the first reactor 8 to excite the first reactor 8, and also repeatedly performs an operation of discharging the excitation to charge the first and second capacitors with a voltage higher than the peak voltage of the first AC power supply 6. By controlling the on and off widths, the waveform of the AC current of the first AC power supply 6 is made similar to the waveform of the AC voltage. As a result, the power factor is improved.

[0021] The efficiency can be improved by reducing the voltage drop of the first bidirectional switch circuit.

[0022] FIG. 2 is a circuit diagram showing an embodiment of the invention described in claim 2. In the figure, reference numerals 1 to 10 are the same components as 1 to 10 in FIG. 1. 7 is a missing number in any figure.

[0023] 11 and 12 in FIG. 2 are the third and fourth diodes respectively, 13 is the second AC power supply, 15 is the second reactor, 16 is the second bidirectional switch circuit, and 17 is the second control circuit.

[0024] The operations of 11 to 13 and 15 to 17 in FIG. 2 are the same as those of the corresponding components other than 3, 4, and 5 in FIG. 1. The first and second capacitors are charged by the voltage doubling rectifier circuit of the first AC power supply, and the first and second capacitors are also charged by the voltage doubling rectifier circuit of the second AC power supply. Therefore, the DC voltage across the series circuit of the first and second capacitors is the same as the value obtained by full-wave rectifying the voltage across the series circuit of the first and second AC power supplies.

[0025] That is, in the single-phase three-wire type, which is the AC power supply method in Japan, when using the power factor improvement circuit of FIG. 1 or FIG. 2, the converted voltage can be selected from 340V to 380V whether the input is 100V or 200V.

[0026] The circuit operation of Figure 1 will be explained using Figure 3. As shown in A in the figure, when the first AC power supply 6 is outputting a positive half-wave of AC voltage and the first bidirectional switch circuit 9 is ON, current flows through the path indicated by ▲1▼. At this time, the first reactor 8 is excited and excitation energy is stored. Next, when the first bidirectional switch circuit 9 is turned OFF, the excitation energy of the first reactor is released and current flows through the path indicated by ▲2▼, charging the first capacitor 3. The currents ▲1▼ and ▲2▼ flow repeatedly, and the power factor is improved by the first control circuit 10 controlling the ON / OFF period so that the current between positive half-waves is similar to the voltage of the first AC power supply.

[0027] Figure 3B shows the current path when the AC voltage is outputting a negative half-wave. ▲1▼ is the current path when the first bidirectional switch circuit 9 is ON, and ▲2▼ is the current path when it is OFF. The current in ▲2▼ charges the second capacitor 4.

[0028] In the first bidirectional switch circuit 9 in Figure 3, the sources of the two N-channel MOSFETs are connected to each other, and the gates of each other are also connected. Therefore, when a signal is applied between the gate and source, both MOSFETs turn on when the circuit is ON, and both MOSFETs turn off when the circuit is OFF.

[0029] Figure 4 is a circuit diagram showing one example of a method for detecting the output voltage in the bridgeless power factor correction circuit of Figure 1. The control terminals of the first bidirectional switch circuit 9 are the gates and sources of the two MOSFETs, both of which constantly change with respect to the output voltage at the switching frequency. Therefore, the diodes 21 and 22 and capacitor 23 added in Figure 4 create a voltage that is approximately equal to the voltage charging capacitor 3 or capacitor 4. Since one terminal of capacitor 23 is at the same potential as the sources of the two MOSFETs, the output voltage can be stabilized by detecting the voltage at the other terminal and controlling the ON width of the first bidirectional switch circuit 9.

[0030] Figure 5 is a circuit diagram showing an example of a conventional method. It is a reference to Figure 1 from the diagram of the bridgeless power factor correction circuit provided in Patent Document 1.

[0031] In Figure 5, MOSFETs Q51 and Q52 connect their drains to each other, forming a bidirectional switch circuit, although the ON-state timing differs from that of the present invention. The function of these two MOSFETs is described in paragraph

[0029] , line 7 of the [Modes for Carrying Out the Invention] section as follows: "During the positive half-cycle period of the power supply voltage from the AC power supply 50, the second switching element Q52 is kept in the ON state at all times, and the first switching element Q51 is switched at high speed." It is explained as, "So,..."

[0032] Paragraph

[0021] of Patent Document 2 explains that "as described above, the control circuit 8 performs control to keep the FET 14 in a constantly ON state, while performing control to cause the FET 12 to perform a switching operation (on / off operation)."

[0033] Paragraph

[0010] of Patent Document 3 states from the 5th line onward that "either N-channel MOSFET Q1 or Q2 performs active switch and synchronous rectification switch operation."

[0034] In other words, Patent Documents 1 to 3 all describe a method in which one of two MOSFETs is turned on in synchronization with the AC cycle, while the other is switched on. This requires synchronizing the two MOSFETs with the AC cycle, switching them to improve the power factor, and, if one of the MOSFETs is floating above the reference potential, driving the gate with an isolated signal, which complicates the control.

[0035] On the other hand, in this application, since the gates and sources of the two MOSFETs are connected to each other, switching can be performed with a single signal, and there is no need to create a signal synchronized with AC, so the control circuit can be constructed using a commercially available power factor correction IC. [Explanation of Symbols]

[0036] 1, 2, 11, 12, 21, 22 diodes 3, 4, 23 Capacitors 5 load 6, 13 AC power supply 8, 15 Reactor 9, 16 Bidirectional switch circuit 10, 17 Control circuits

Claims

1. A voltage doubler rectifier circuit is characterized in that a first diode and a second diode are connected in series with their orientations aligned, a series circuit consisting of a first capacitor and a second capacitor is connected in parallel to the series circuit consisting of the first diode and the second diode, a load is connected in parallel to the series circuit consisting of the first capacitor and the second capacitor, a first AC power supply is connected between the connection point of the first diode and the second diode and the connection point of the first capacitor and the second capacitor, thereby converting the AC power of the first AC power supply into DC power and supplying it to the load, a first reactor is inserted in series to one output terminal of the first AC power supply, a first bidirectional switch circuit is connected between the connection point of the first diode and the second diode and the connection point of the first capacitor and the second capacitor, and a first control circuit is added that applies an on / off signal to the control electrode of the first bidirectional switch circuit, thereby improving the power factor of the output current of the first AC power supply.

2. A bridgeless power factor correction circuit characterized by connecting a third diode and a fourth diode in series with their orientations aligned, connecting the series circuit of the third diode and the fourth diode in parallel to the series circuit of the first diode and the second diode, connecting one output terminal of a second AC power supply whose voltage and phase match that of the first AC power supply to the output terminal of the first AC power supply opposite to the output terminal to which the first reactor is connected, and connecting the other output terminal to the connection point of the third diode and the fourth diode, inserting a second reactor in series to the output terminal of the second AC power supply opposite to the output terminal of the first AC power supply, connecting a second bidirectional switch circuit between the connection point of the third diode and the fourth diode and the connection point of the first capacitor and the second capacitor, and adding a second control circuit that applies an on / off signal to the control electrode of the second bidirectional switch circuit, thereby improving the power factor of the output current of the second AC power supply.

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