Control circuit for bridgeless PFC circuit, control method therefor, and power supply system

A control method for a bridgeless power factor correction (PFC) circuit, wherein the control method is applied to a control circuit for the bridgeless PFC circuit, wherein the bridgeless PFC circuit comprises a first bridge arm, the first bridge arm comprises a first switch transistor and a second switch transistor that are connected in series, the first switch transistor is configured to be turned on under control of a driving signal having a high level, and the second switch transistor is configured to be turned on under control of a driving signal having a low level;

• and the control circuit comprises a polarity determination module and a logic control module, wherein the polarity determination module comprises a voltage division circuit, a third switch transistor, and a power supply;
• the voltage division circuit has a first connection end configured to receive a sampling signal of an alternating current (AC) input voltage of the bridgeless PFC circuit, the voltage division circuit has a second connection end for grounding, and the voltage division circuit comprises a voltage division element;
• the third switch transistor comprises a control electrode, a first conduction electrode, and a second conduction electrode;
• the control electrode is connected to a first connection end of the voltage division element and the first conduction electrode is connected to a second connection end of the voltage division element, the power supply is connected between the second conduction electrode and a ground, and a connection node between the power supply and the second conduction electrode is connected to the logic control module;
• when the sampling signal is a positive voltage signal, the third switch transistor is turned on, and a first digital signal having a low level is output at the connection node between the power supply and the second conduction electrode;
• when the sampling signal is a negative voltage signal, the third switch transistor is cut off, and a second digital signal having a high level is output at the connection node between the power supply and the second conduction electrode;
• and the logic control module is configured to receive a preset pulse signal, the first digital signal, and the second digital signal;
• the logic control module is configured to output a first driving signal to the bridgeless PFC circuit to control the second switch transistor to be turned on, when receiving the first digital signal and the preset pulse signal having a low level, and the logic control module is configured to output a second driving signal to the bridgeless PFC circuit to control the first switch transistor to be turned on, when receiving the second digital signal and the preset pulse signal having a high level;
• and a changing period of a level of the preset pulse signal is the same as a changing period of a polarity of the AC input voltage;
• wherein the control method comprises:
• receiving, with the polarity determination module, the sampling signal of the AC input voltage of the bridgeless PFC circuit;
• outputting the first digital signal having a low level when the sampling signal is a positive voltage signal, and outputting the second digital signal having a high level when the sampling signal is a negative voltage signal;
• and receiving, with the logic control module, the preset pulse signal, the first digital signal, and the second digital signal;
• outputting the first driving signal to the bridgeless PFC circuit to control the second switch transistor to be turned on, when receiving the first digital signal and the preset pulse signal having a low level, and outputting the second driving signal to the bridgeless PFC circuit to control the first switch transistor to be turned on, when receiving the second digital signal and the preset pulse signal having a high level;
• and the level polarity of the preset pulse signal changes periodically.

A power supply system, comprising a bridgeless power factor correction (PFC) circuit, wherein the bridgeless PFC circuit comprises a first bridge arm, the first bridge arm comprises a first switch transistor and a second switch transistor that are connected in series, the first switch transistor is configured to be turned on under control of a driving signal having a high level, and the second switch transistor is configured to be turned on under control of a driving signal having a low level a control circuit, wherein the control circuit comprises a polarity determination module and a logic control module, wherein the polarity determination module comprises a voltage division circuit, a third switch transistor, and a power supply;

• the voltage division circuit has a first connection end configured to receive a sampling signal of an alternating current (AC) input voltage of the bridgeless PFC circuit, the voltage division circuit has a second connection end for grounding, and the voltage division circuit comprises a voltage division element;
• the third switch transistor comprises a control electrode, a first conduction electrode, and a second conduction electrode;
• the control electrode is connected to a first connection end of the voltage division element and the first conduction electrode is connected to a second connection end of the voltage division element, the power supply is connected between the second conduction electrode and a ground, and a connection node between the power supply and the second conduction electrode is connected to the logic control module;
• when the sampling signal is a positive voltage signal, the third switch transistor is turned on, and a first digital signal having a low level is output at the connection node between the power supply and the second conduction electrode;
• when the sampling signal is a negative voltage signal, the third switch transistor is cut off, and a second digital signal having a high level is output at the connection node between the power supply and the second conduction electrode;
• and the logic control module is configured to receive a preset pulse signal, the first digital signal, and the second digital signal;
• the logic control module is configured to output a first driving signal to the bridgeless PFC circuit to control the second switch transistor to be turned on, when receiving the first digital signal and the preset pulse signal having a low level, and the logic control module is configured to output a second driving signal to the bridgeless PFC circuit to control the first switch transistor to be turned on, when receiving the second digital signal and the preset pulse signal having a high level;
• and a changing period of a level of the preset pulse signal is the same as a changing period of a polarity of the AC input voltage;
• a sampling circuit, configured to collect the sampling signal of the AC input voltage of the bridgeless PFC circuit and send the sampling signal to the polarity determination module;
• a digital control chip, configured to generate the preset pulse signal and send the preset pulse signal to the logic control module.