CN101958550A - Bridgeless power factor correction circuit system with current detection circuit and method thereof - Google Patents

Abstract

The present invention discloses a bridgeless power factor correction (PFC) circuit system, comprising a bridgeless PFC circuit having a first and a second switch and an inductor for receiving an AC input voltage and generating a DC output voltage, a current sensing circuit, comprising a first inverter having a primary winding, a first secondary winding and a second secondary winding, wherein the primary winding is coupled to the second switch, and the first inverter is used to sense a first current flowing through the inductor and the first and the second switches.

Description

Bridgeless power factor correction circuit system with current detection circuit and method thereof

technical field

The invention relates to a current detection circuit and a method thereof in a bridgeless power factor correction (Bridgeless PFC) circuit system, in particular to a current detection circuit in an H-bridge PFC circuit system and a control method thereof.

Background technique

The loss of the rectifier bridge in the traditional boost power factor correction (Boost PFC) circuit has become one of the main losses of the entire switching power supply. As the requirements for conversion efficiency increase, the bridgeless Boost circuit derived from the traditional Boost PFC circuit has gradually become a research hotspot. It omits the rectifier bridge at the front end of Boost PFC, so that there are only two diodes in the working circuit, which reduces the on-state loss of one diode and improves efficiency. The H-PFC circuit is a bridgeless PFC circuit suitable for medium and high power (as shown in the first figure). 1 includes an inductor L, four diodes D1-D4, two switches Q1-Q2, and an output capacitor CB for receiving an AC input voltage Vin and generating a DC output voltage Vo.

Figures 2a and 2b respectively show the positive and negative half-cycle working states of an H-PFC circuit shown in Figure 1 within a power frequency cycle of an AC input voltage. The drive signals for switches Q1 and Q2 are in phase. In Fig. 2a, when the AC input voltage Vin is in positive half cycle, L1, D1, D4, Q1, Q2 and CB form a boost circuit, wherein D4 and Q2 are normally on. When Q1 is turned on, the current flows back through L1, Q1 and Q2; when Q1 is turned off, the current flows back through L1, D1, CB and D4. In Figure 2b, when the input voltage Vin is in negative half cycle, L1, D2, Q1, Q2, D3 and CB form another Boost circuit, in which Q1 and D3 are normally on. When Q2 is turned on, the current flows back through L1, Q1 and Q2; when Q2 is turned off, the current flows back through L1, D3, CB and D2. During positive and negative half cycles of the AC input voltage, the current directions of L1, Q1 and Q2 are opposite. Since D3 and D4 clamp the AC to the output capacitor CB of the Boost circuit, the same common-mode noise as that of the traditional Boost PFC circuit can be obtained. Since the current only passes through two components at any working moment in a switching cycle, the conduction loss is reduced.

For this reason, in view of the lack of conventional technology, the inventor thought about and improved the idea of the invention, and finally invented the "bridgeless power factor correction circuit system with current detection circuit and its method" of this case.

Contents of the invention

The main purpose of this case is to provide a bridgeless PFC circuit system with a current detection circuit and its method for detecting the current flowing through the switches and inductors of the PFC circuit. The current detection circuit has a simple circuit structure and method and low cost It can also be used in occasions that require strong anti-interference ability, high power or high requirements for current signal sampling.

Another main purpose of this case is to provide a bridgeless power factor correction (PFC) circuit system, including a bridgeless PFC circuit, with a first and a second switch and an inductor, for receiving an AC input voltage and generating A DC output voltage, a current sensing circuit, including a first converter with a primary winding, a first secondary winding and a second secondary winding, wherein the primary winding is coupled to the first secondary winding Two switches, the first secondary side and the second secondary side winding each have a first end and a second end, and the inverter is used for sensing a flow through the inductor and the first and the second switch The first current, a first resistance, has a first end and a second end, wherein the first end is coupled to the first end of the first secondary side winding, and the second end is coupled to the second end The second terminal of a secondary winding and the first terminal of the second secondary winding, and a second resistor having a first terminal and a second terminal, wherein the first terminal is coupled to the first terminal The second end of a resistor is coupled to the second end of the second secondary winding.

According to the above idea, the current sensing circuit further includes a second converter with a primary winding coupled to the bridgeless PFC circuit for sensing a second current flowing through the inductor, the bridgeless The PFC circuit is a first and a second input terminal, a first and a second output terminal, a first bridge arm including a first and a second diode and a first midpoint, a An H-PFC circuit comprising a third and a fourth diode, a second bridge arm of a second midpoint, and an output capacitor, each of the first and the second switch, the inductor, and the output capacitor has a First end and a second end, the first to the fourth diodes each have an anode and a cathode, the anode of the first diode and the cathode of the second diode are coupled to the first A midpoint, the cathode of the first diode and the cathode of the third diode are coupled to the primary side winding of the second inverter, the anode of the third diode is connected to the fourth The cathode of the diode is coupled to the second midpoint, the first end of the output capacitor is coupled to the first winding and the first output end of the second converter, the second diode The anode and the anode of the fourth diode are coupled to the second terminal of the output capacitor and the second output terminal, the primary side winding of the first inverter is coupled to the second midpoint, and the second The first end of the switch is coupled to the primary side winding of the first inverter, the second end of the first switch is coupled to the second end of the second switch, the first end of the inductor is coupled to The first input terminal, the second terminal of the inductor are coupled to the first midpoint, and the second midpoint is coupled to the second input terminal.

According to the idea above, the current sensing circuit further includes a third resistor and a third switch each having a first end and a second end, and fifth and sixth resistors each having an anode and a cathode. diode, the first end of the first secondary winding is coupled to the cathode of the fifth diode, the second end of the first secondary winding is coupled to the first of the third switch end, the second end of the second secondary winding is coupled to the cathode of the sixth diode, the anode of the fifth diode is coupled to the anode of the sixth diode and the third the first end of the resistor, and the second end of the third switch is coupled to the second end of the third electrical group and grounded.

According to the above idea, the first current and the second current are accumulated to form a current signal flowing through the inductor, and the current signal is a sawtooth wave with a sinusoidal envelope.

According to the above idea, the second converter further includes a secondary winding with a first end and a second end, the first end of the secondary winding is coupled to the second end of the third resistor. end, the current sensing circuit further includes a seventh diode with an anode and a cathode, the second end of the secondary winding is coupled to the cathode of the seventh diode, and the seventh second The anode of the transistor is coupled to the first end of the third resistor.

According to the above idea, the first current and the second current are accumulated to form a current signal flowing through the inductor, and the current signal is a triangular wave with a sinusoidal envelope.

According to the idea above, the current sensing circuit further includes a third resistor each having a first end and a second end, a third and a fourth switch, and a fifth resistor each having an anode and a cathode. and a sixth diode, the first end of the first secondary winding is coupled to the anode of the fifth diode, the second end of the first secondary winding is coupled to the third resistor The second terminal of the second secondary winding is coupled to the anode of the sixth diode, and the cathode of the fifth diode is coupled to the first terminal of the third switch , the cathode of the sixth diode is coupled to the first terminal of the four switches, the second terminal of the third switch is coupled to the second terminal of the fourth switch and the first terminal of the third resistor , and the second end of the third resistor is grounded.

Another main purpose of this case is to provide a bridgeless power factor correction (PFC) circuit system, including a bridgeless PFC circuit, with a first and a second switch and an inductor, used to receive an AC input voltage and generate A DC output voltage, a current sensing circuit, including a first converter with a primary winding, a first secondary winding and a second secondary winding, wherein the primary winding is coupled to the first secondary winding Two switches, and the first inverter is used for sensing a first current passing through the inductor.

According to the above idea, the current sensing circuit further includes a second converter with a primary winding coupled to the bridgeless PFC circuit for sensing a second current flowing through the inductor, the bridgeless The PFC circuit is a first and a second input terminal, a first and a second output terminal, a first bridge arm including a first and a second diode and a first midpoint, a An H-PFC circuit comprising a third and a fourth diode, a second bridge arm of a second midpoint, and an output capacitor, each of the first and the second switch, the inductor, and the output capacitor has a First end and a second end, the first to the fourth diodes each have an anode and a cathode, the anode of the first diode and the cathode of the second diode are coupled to the first A midpoint, the cathode of the first diode and the cathode of the third diode are coupled to the primary side winding of the second inverter, the anode of the third diode is connected to the fourth The cathode of the diode is coupled to the second midpoint, the first end of the output capacitor is coupled to the first winding and the first output end of the second converter, the second diode The anode and the anode of the fourth diode are coupled to the second terminal of the output capacitor and the second output terminal, the primary side winding of the first inverter is coupled to the second midpoint, and the second The first end of the switch is coupled to the primary side winding of the first inverter, the second end of the first switch is coupled to the second end of the second switch, the first end of the inductor is coupled to The first input terminal, the second terminal of the inductor are coupled to the first midpoint, and the second midpoint is coupled to the second input terminal.

According to the above idea, the first secondary side and the second secondary side winding each have a first end and a second end, and the current sensing circuit further includes a first end and a second end each a first to a third resistor and a third switch, and a fifth and a sixth diode each having an anode and a cathode, the first end of the first secondary winding is coupled to the first The first end of a resistor is coupled to the cathode of the fifth diode, the second end of the first secondary winding is coupled to the first end of the second secondary winding, the first resistor The second terminal, the first terminal of the second resistor and the first terminal of the third switch, the second terminal of the second secondary side winding are coupled to the second terminal of the second resistor and the first terminal of the third switch. The cathode of the sixth diode, the anode of the fifth diode are coupled between the anode of the sixth diode and the first end of the third resistor, and the second end of the third switch coupled to the second end of the third electrical group and grounded.

According to the above idea, the second converter further includes a secondary winding with a first end and a second end, the first end of the secondary winding is coupled to the second end of the third resistor. end, the current sensing circuit further includes a seventh diode with an anode and a cathode, the second end of the secondary winding is coupled to the cathode of the seventh diode, and the seventh second The anode of the transistor is coupled to the first end of the third resistor.

According to the above idea, the first secondary side and the second secondary side winding each have a first end and a second end, and the current sensing circuit further includes a first end and a second end each A first to a third resistor and a third and a fourth switch, and a fifth and a sixth diode each having an anode and a cathode, the first end of the first secondary winding coupled to the first terminal of the first resistor and the anode of the fifth diode, the second terminal of the first secondary winding is coupled to the first terminal of the second secondary winding, the The second terminal of the first resistor, the first terminal of the second resistor and the second terminal of the third resistor, the second terminal of the second secondary side winding are coupled to the first terminal of the second resistor Two terminals are connected to the anode of the sixth diode, the cathode of the fifth diode is coupled to the first end of the third switch, and the cathode of the sixth diode is coupled to the fourth switch. The first end, the second end of the third switch are coupled to the second end of the fourth switch and the first end of the third resistor, and the second end of the third resistor is grounded, and the current The sensing circuit needs to perform a phase detection.

A main purpose of the present case is to provide a control method for a bridgeless power factor correction (PFC) circuit system, wherein the bridgeless PFC circuit system includes a current sensing circuit with a first converter, a Inductor, a first and a second switch, a first to a fourth diode and an output capacitor, the method includes the following steps: (a) providing an AC input voltage, and the voltage is in a positive half cycle; (b) When the first switch and the second switch are turned on, the inductor, the first switch and the second switch, and the first converter are electrically connected in series to form a first loop, and through the second switch an inverter measures a first inductor current flowing through the first loop; and (c) when the first and the second switches are turned off, the inductor, the first diode, the output capacitor and The fourth diode is electrically connected in series to form a second loop, and a second inductor current flowing through the second loop is measured.

According to the above idea, the step (b) further includes the following steps: (b1) providing a duty ratio of n between the secondary side and the primary side of the first inverter, and the third resistor One of the resistance values is R3; (b2) when the first and the second switches are turned on, a sampling current flowing through the third resistance is the first inductor current*(-n)*R3; and ( b3) Obtaining the first inductor current by the sampling current flowing through the third resistor.

According to the above idea, the second loop further includes the second converter electrically connected in series with the first diode and the output capacitor for measuring the second inductor current, the first inductor current and the second The inductor current is accumulated to form a current signal flowing through the inductor, and the current signal is a sawtooth wave with a sinusoidal envelope.

According to the above idea, the step (c) further includes the following steps: (c1) providing a duty ratio of n between the secondary side and the primary side of the second converter, and the third resistor A resistance value is R3; and (c2) when the first switch and the second switch are turned on, a sampling current flowing through the third resistance is the second inductor current*(-n)*R3; and (c3) Obtaining the second inductor current by the sampling current flowing through the third resistor.

According to the above idea, the first inductor current and the second inductor current are accumulated to form a current signal flowing through the inductor, and the current signal is a triangular wave with a sinusoidal envelope.

In order to make the above-mentioned purposes, features, and advantages of the present invention more obvious and understandable, the preferred embodiments are specifically cited below, and in conjunction with the accompanying drawings, the detailed description is as follows:

Description of drawings

Fig. 1 is the circuit diagram of the H-PFC circuit of prior art;

Figures 2a and 2b are the working states of the H-PFC circuit shown in Figure 1 in a power frequency cycle of an input voltage;

3a and 3b are respectively a circuit diagram of a main circuit and a current detection circuit of a H-PFC circuit according to a first preferred embodiment of the concept of the present invention;

Figure 3c is a waveform diagram of the current detection circuit shown in 3b for detecting a sawtooth wave with a sine envelope;

4 is a working waveform diagram of the main circuit and the current detection circuit of the H-PFC circuit according to the first preferred embodiment of the conception of the present invention in the positive half cycle of the power frequency cycle of an AC input voltage;

5a and 5b are circuit schematic diagrams of the first and second working stages of the main circuit and the current detection circuit shown in FIGS. 3a and 3b in the positive half cycle of the power frequency cycle of an AC input voltage;

6a and 6b are circuit diagrams of the main circuit and the current detection circuit of the H-PFC circuit according to the second preferred embodiment of the present invention;

Fig. 6c is a waveform diagram of a triangular wave with a sinusoidal envelope by the current detection circuit shown in 6b;

7 is a working waveform diagram of the main circuit and the current detection circuit of the H-PFC circuit according to the second preferred embodiment of the present invention in the positive half cycle of the power frequency cycle of an AC input voltage;

8 is a schematic circuit diagram of the second working phase of the main circuit and the current detection circuit of the H-PFC circuit according to the second preferred embodiment of the concept of the present invention in the positive half cycle of the power frequency cycle of an AC input voltage; and

FIG. 9 is a circuit diagram of a current detection circuit of an H-PFC circuit according to a third preferred embodiment of the concept of the present invention.

Detailed ways

3a and 3b respectively show a circuit diagram of a main circuit and a current detection circuit of an H-PFC circuit system according to a first preferred embodiment of the concept of the present invention. The main circuit applying this current detection circuit is shown in Figure 3a. The difference between Fig. 3a and Fig. 1 is that it adds a converter (CT) CT1. The first preferred embodiment uses a current signal detection circuit as shown in FIG. 3b to detect the Q1 and Q2 currents of the H-PFC circuit shown in FIG. 3a. The current detection circuit shown in Figure 3b is used to detect a sawtooth wave with a sinusoidal envelope, the sawtooth wave is shown in Figure 3c. In addition to the first winding CT1_1 and the second winding CT1_2 of the secondary side of the converter CT1, this detection circuit also includes R1, R2, D5, D6, R3 and Q3, and the driving signal of Q3 is the same as that of the main power switch Q1 and Q2 The drive signal is the same.

FIG. 4 shows a working waveform diagram of the main circuit and the current detection circuit of the H-PFC circuit system according to the first preferred embodiment of the concept of the present invention in the positive half cycle of the power frequency cycle of an AC input voltage. The gate driving signals Q1, Q2, Q3 are the waveforms of the gate driving signals of the switches Q1, Q2 and Q3 (all of them are MOSFETs), iL is the current on the inductor, and I1 is the current through the switching tube Q1 and The current of Q2 is the current of CT1 primary side. Figures 5a and 5b respectively show a schematic circuit diagram of the main circuit and the current detection circuit shown in Figures 3a and 3b in the first and second working stages of the positive half cycle of the power frequency cycle of an AC input voltage, showing the circuit diagrams shown in Figure 3a The specific analysis of the working state of the circuit shown in and 3b in the positive half cycle of the AC input voltage. The analysis of the working state of the circuit during the negative half cycle of the AC input voltage is similar to that during the positive half cycle. n is the turns ratio between the secondary side and the primary side of the converter CT1 (the primary side of the CT is on the main circuit side, and the secondary side of the CT is on the sampling circuit side).

As shown in Figure 5a, in the first working stage of the circuit, the three switches Q1, Q2 and Q3 are turned on at the same time, and the current flows back through L1, Q1, Q2 and CT1. During this period, the current on the primary side of CT1 is IL, and the current on the secondary side of CT1 is nIL; the current of CTI_1 on the secondary side returns through Q3, R3 and D5, and the current on CT1_2 on the secondary side flows back through R2, so The voltage on the sampling resistor R3 is -nILR3.

As shown in Figure 5b, it is the second working stage of the H-PFC circuit. After the switches Q1, Q2 and Q3 are turned off simultaneously, the current flows back through L, D1, CB and D4. During this period, since Q3 is turned off, the secondary side windings of CT1: the first secondary side winding CT1_1 and the second secondary side winding CT1_2 are disconnected from the sampling resistor R3, so CT1 has no influence on the circuit. In this way, we can detect the current on the main power components Q1 and Q2, and it can be detected accurately without phase detection. This method only uses one CT1 in this working stage, and its circuit structure is relatively simple.

In order to obtain the current waveform on the inductor, on the basis of the original CT1, another converter CT2 needs to be added. CT2 is between the rectifier bridge D1, D2, D3, D4 and the capacitor CB to form another current signal sampling circuit. As shown in Fig. 6b, it is the second preferred embodiment of the present invention, and its main circuit is shown in Fig. 6a. The current signal sampling circuit samples a triangular wave current signal with a sinusoidal envelope, and the triangular wave current signal is shown in FIG. 6c. When the switches Q1, Q2 and Q3 are turned on simultaneously, as shown in FIG. 5a, it is the same as the first embodiment. After MOSFET Q1, Q2 and Q3 are turned off at the same time, the current flows through L, D1, CT2, CB and D4 return. During this period, the current of CT2 is IL, and the current of the secondary side of CT2 is -nIL; the current flowing through the secondary side of CT2 flows back through R3 and D7, so the voltage on the sampling resistor R3 is -nILR3, as shown in Figure 6b Show. The current signals of the switches Q1, Q2, and Q3 are sampled and accumulated during the two time periods when the switches Q1, Q2, and Q3 are turned on and turned off to form a current signal on the inductor. In this way, we can detect the current on the inductor by using only two CTs such as CT1 and CT2.

7 shows a working waveform diagram of the main circuit and the current detection circuit of the H-PFC circuit system according to the second preferred embodiment of the present invention in the positive half cycle of the power frequency cycle of an AC input voltage. Fig. 8 shows that the main circuit and the current detection circuit of the H-PFC circuit system according to the second preferred embodiment of the conception of the present invention include current paths, etc. in the second working phase of the positive half cycle of the power frequency cycle of an AC input voltage The schematic diagram of the circuit, and I1+I2 in Figure 7 is the waveform diagram of the sampling and accumulation of the current signal during the two times of switching on and off of the switch tubes Q1, Q2 and Q3.

The present invention can also be constructed by replacing the switch Q3 in FIG. 3 b with two switches Q4 and Q5 , as shown in FIG. 9 . 9 shows a circuit diagram of the current detection circuit of the H-PFC circuit system according to the third preferred embodiment of the present invention, wherein the anode of the diode D5 is coupled to the first end of the resistor R1, and the cathode of the diode D5 is coupled to the switch. The first terminal of Q4, the anode of diode D6 are coupled to the second terminal of resistor R2, and the cathode of diode D6 is coupled to the first terminal of switch Q5, and the second terminals of switches Q4 and Q5 are both coupled to the first terminal of resistor R3 , which is the difference between Figure 9 and Figure 3b. In this way, the anti-interference ability of the current detection circuit is stronger, and it can be used in occasions with high power or higher requirements on current signal sampling (such as digital control), but phase detection is required.

The present invention utilizes the above-mentioned current detection circuits, without adding a control circuit, and can sample a triangular wave or sawtooth wave signal with a sine envelope. The method is simple, low-cost and accurate in detection.

In summary, the present invention discloses a bridgeless PFC circuit with a current detection circuit and its control method, which are used to detect the current flowing through the switches and inductors of the PFC circuit. The current detection circuit has a simple circuit structure and method , low cost and accurate detection, etc., and can also be used in occasions that require strong anti-interference ability, high power, or high requirements for current signal sampling, so it does have its progress and novelty.

Therefore, even if the present case has been described in detail by the above-mentioned embodiment and can be modified in various ways by the people who are familiar with the art, all of them are not deviating from the intended protection of the scope of the attached patent application.

Claims (17)

1. A bridgeless power factor correction (PFC) circuit system, characterized in that, comprising: A bridgeless PFC circuit with a first and a second switch and an inductance for receiving an AC input voltage and generating a DC output voltage; A current sensing circuit, comprising: A first converter with a primary winding, a first secondary winding and a second secondary winding, wherein the primary winding is coupled to the second switch, the first secondary and the second Each of the two secondary side windings has a first end and a second end, and the inverter is used for sensing a first current passing through the inductor and the first and second switches; A first resistor with a first end and a second end, wherein the first end is coupled to the first end of the first secondary winding, and the second end is coupled to the first secondary winding the second end of the second secondary winding and the first end of the second secondary winding; and A second resistor has a first terminal and a second terminal, wherein the first terminal is coupled to the second terminal of the first resistor, and the second terminal is coupled to the first terminal of the second secondary winding. Two ends. 2. A bridgeless power factor correction (PFC) circuit system as claimed in claim 1, wherein the current sensing circuit further comprises a primary winding coupled to the bridgeless PFC circuit, and A second converter for sensing a second current passing through the inductor, the bridgeless PFC circuit has a first and a second input terminal, a first and a second output terminal, and a H -PFC circuit, the first and the second switch, the inductor and the output capacitor each have a first end and a second end, the first to the fourth diodes each have an anode and a cathode, the The anode of the first diode is coupled to the cathode of the second diode at the first midpoint, and the cathode of the first diode is coupled to the cathode of the third diode at the second The primary side winding of the inverter, the anode of the third diode and the cathode of the fourth diode are coupled to the second midpoint, the first terminal of the output capacitor is coupled to the second inverter The first winding and the first output end of the current transformer, the anode of the second diode and the anode of the fourth diode are coupled to the second end of the output capacitor and the second output end, The primary winding of the first inverter is coupled to the second midpoint, the first end of the second switch is coupled to the primary winding of the first inverter, and the second terminal is coupled to the second terminal of the second switch, the first terminal of the inductor is coupled to the first input terminal, the second terminal of the inductor is coupled to the first midpoint, and the second midpoint is coupled to the the second input. 3. A bridgeless power factor correction (PFC) circuit system as claimed in claim 2, wherein the current sensing circuit further comprises a third resistor each having a first terminal and a second terminal and a third switch, and fifth and sixth diodes each having an anode and a cathode, the first end of the first secondary winding being coupled to the cathode of the fifth diode, The second terminal of the first secondary winding is coupled to the first terminal of the third switch, the second terminal of the second secondary winding is coupled to the cathode of the sixth diode, and the first terminal of the second secondary winding is coupled to the cathode of the sixth diode. The anode of the fifth diode is coupled to the anode of the sixth diode and the first end of the third resistor, and the second end of the third switch is coupled to the second end of the third resistor. terminal and grounded. 4. A bridgeless power factor correction (PFC) circuit system as claimed in claim 3, wherein the first current and the second current are accumulated to form a current flowing through the inductor signal, and the current signal is a sawtooth wave with a sinusoidal envelope. 5. A bridgeless power factor correction (PFC) circuit system as claimed in claim 3, wherein the second converter further comprises a secondary side with a first terminal and a second terminal winding, the first end of the secondary winding is coupled to the second end of the third resistor, the current sensing circuit further includes a seventh diode with an anode and a cathode, the secondary winding The second terminal of the second resistor is coupled to the cathode of the seventh diode, and the anode of the seventh diode is coupled to the first terminal of the third resistor. 6. A bridgeless power factor correction (PFC) circuit system as claimed in claim 5, wherein the first current and the second current are accumulated to form a current flowing through the inductor signal, and the current signal is a triangular wave with a sinusoidal envelope. 7. A bridgeless power factor correction (PFC) circuit system as claimed in claim 2, wherein the current sensing circuit further comprises a third resistor each having a first terminal and a second terminal and a third and a fourth switch, and a fifth and a sixth diode each having an anode and a cathode, the first end of the first secondary winding being coupled to the fifth diode the anode of the first secondary winding, the second end of the first secondary winding is coupled to the second end of the third resistor, the second end of the second secondary winding is coupled to the sixth diode anode, the cathode of the fifth diode is coupled to the first terminal of the third switch, the cathode of the sixth diode is coupled to the first terminal of the four switches, the first terminal of the third switch Two terminals are coupled between the second terminal of the fourth switch and the first terminal of the third resistor, and the second terminal of the third resistor is grounded. 8. A bridgeless power factor correction (PFC) circuit system, characterized in that it comprises: A bridgeless PFC circuit with a first and a second switch and an inductance for receiving an AC input voltage and generating a DC output voltage; A current sensing circuit, comprising: A first inverter has a primary winding, a first secondary winding, and a second secondary winding, wherein the primary winding is coupled to the second switch, and the first inverter is used for sensing A first current flowing through the inductor is measured. 9. A bridgeless power factor correction (PFC) circuit system as claimed in claim 8, wherein the current sensing circuit further comprises a primary winding coupled to the bridgeless PFC circuit, and A second converter for sensing a second current passing through the inductor, the bridgeless PFC circuit has a first and a second input terminal, a first and a second output terminal, and a H -PFC circuit, the first and the second switch, the inductor and the output capacitor each have a first end and a second end, the first to the fourth diodes each have an anode and a cathode, the The anode of the first diode is coupled to the cathode of the second diode at the first midpoint, and the cathode of the first diode is coupled to the cathode of the third diode at the second The primary side winding of the inverter, the anode of the third diode and the cathode of the fourth diode are coupled to the second midpoint, the first terminal of the output capacitor is coupled to the second inverter The first winding and the first output end of the current transformer, the anode of the second diode and the anode of the fourth diode are coupled to the second end of the output capacitor and the second output end, The primary winding of the first inverter is coupled to the second midpoint, the first end of the second switch is coupled to the primary winding of the first inverter, and the second terminal is coupled to the second terminal of the second switch, the first terminal of the inductor is coupled to the first input terminal, the second terminal of the inductor is coupled to the first midpoint, and the second midpoint is coupled to the the second input. 10. A bridgeless power factor correction (PFC) circuit system as claimed in claim 9, wherein the first secondary side and the second secondary side winding each have a first terminal and a first terminal Two terminals, the current sensing circuit further includes first to third resistors and a third switch each having a first terminal and a second terminal, and a fifth and a third switch each having an anode and a cathode a sixth diode, the first end of the first secondary winding is coupled to the first end of the first resistor and the cathode of the fifth diode, the first end of the first secondary winding The two ends are coupled to the first end of the second secondary side winding, the second end of the first resistor, the first end of the second resistor and the first end of the third switch, the second The second end of the secondary winding is coupled to the second end of the second resistor and the cathode of the sixth diode, the anode of the fifth diode is coupled to the sixth diode The anode is coupled to the first end of the third resistor, and the second end of the third switch is coupled to the second end of the third electric set and grounded. 11. A bridgeless power factor correction (PFC) circuit system as claimed in claim 10, wherein the second converter further comprises a secondary side with a first terminal and a second terminal winding, the first end of the secondary winding is coupled to the second end of the third resistor, the current sensing circuit further includes a seventh diode with an anode and a cathode, the secondary winding The second terminal of the second resistor is coupled to the cathode of the seventh diode, and the anode of the seventh diode is coupled to the first terminal of the third resistor. 12. A bridgeless power factor correction (PFC) circuit system as claimed in claim 9, wherein the first secondary side and the second secondary side winding each have a first terminal and a first terminal Two terminals, the current sensing circuit further includes first to third resistors and a third and a fourth switch each having a first terminal and a second terminal, and one of an anode and a cathode each Fifth and a sixth diode, the first terminal of the first secondary side winding is coupled to the first terminal of the first resistor and the anode of the fifth diode, the first secondary side The second end of the winding is coupled to the first end of the second secondary winding, the second end of the first resistor, the first end of the second resistor and the second end of the third resistor , the second end of the second secondary winding is coupled to the second end of the second resistor and the anode of the sixth diode, and the cathode of the fifth diode is coupled to the third switch the first end of the sixth diode, the cathode of the sixth diode is coupled to the first end of the four switches, the second end of the third switch is coupled to the second end of the fourth switch and the third The first end of the resistor and the second end of the third resistor are grounded, and the current sensing circuit needs to perform a phase detection. 13. A control method for a bridgeless power factor correction (PFC) circuit system, wherein the bridgeless PFC circuit system includes a current sensing circuit with a first inverter, an inductor, a first and A second switch, a first to a fourth diode and an output capacitor, characterized in that the method comprises the following steps: (a) Provide an AC input voltage, and the voltage is in a positive half cycle; (b) When the first switch and the second switch are turned on, the inductor, the first switch and the second switch, and the first converter are electrically connected in series to form a first loop, and through the second switch an inverter measures a first inductor current passing through the first loop; and (c) When the first and second switches are turned off, electrically connect the inductor, the first diode, the output capacitor and the fourth diode in series to form a second loop, and measure a current A second inductor current passes through the second loop. 14. A bridgeless power factor correction (PFC) circuit system as claimed in claim 13, wherein the bridgeless PFC circuit system is a bridgeless PFC circuit system as described in item 3 of the scope of patent application , and the step (b) further includes the following steps: (b1) providing that the turns ratio (duty ratios) between the secondary side and the primary side of the first converter is n, and the resistance value of one of the third resistors is R3; (b2) When the first switch and the second switch are turned on, make a sampling current flowing through the third resistor be the first inductor current*(-n)*R3; and (b3) Obtaining the first inductor current by the sampling current flowing through the third resistor. 15. A bridgeless power factor correction (PFC) circuit system as claimed in claim 14, wherein the second loop further comprises the second converter electrically connected in series with the first diode and The output capacitor is used to measure the second inductor current, the first inductor current and the second inductor current are accumulated to form a current signal flowing through the inductor, and the current signal is a sinusoidal envelope The sawtooth wave of the line. 16. A bridgeless power factor correction (PFC) circuit system as claimed in claim 13, wherein the bridgeless PFC circuit system is a bridgeless PFC circuit system as described in item 5 of the scope of patent application , and the step (c) further includes the following steps: (c1) providing that the turns ratio (duty ratios) of one of the secondary side and the primary side of the second converter is n, and a resistance value of one of the third resistors is R3; and (c2) When the first switch and the second switch are turned on, make a sampling current flowing through the third resistor be the second inductor current*(-n)*R3; and (c3) Obtaining the second inductor current by the sampling current flowing through the third resistor. 17. A bridgeless power factor correction (PFC) circuit system as claimed in claim 16, wherein the first inductor current and the second inductor current are accumulated to form a current flowing through the inductor A current signal, and the current signal is a triangular wave with a sinusoidal envelope.

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