Current sense method for bridgeless boost (BLB) PFC circuit using single current transformer
View Patent ↗A circuit and method for improving current sensing in a bridgeless PFC boost converter. Such a converter comprises a current transformer having first and second primaries; a boost inductor having a first end connected to a first AC input terminal and a second end connected to a first junction defined between the anode of a first diode and a first end of the first primary, the second end of the first primary being connected to a first terminal of the first switch; a second terminal of the first switch being connected to a common line; a parallel circuit of a capacitance and a load connected between the cathode of the first diode and the common line; a series circuit of a second diode, the second primary and a second switch connected between the cathode of the first diode and the common line; and a second AC input terminal connected to a second junction defined between the second primary and the second switch. A second boost inductor may be connected between the second AC input terminal and the second junction. The first and second switches may be MOSFETs. The circuit also includes a rectification circuit on first and second secondaries of the current transformer, comprising a MOSFET and additional diodes.
1. A bridgeless PFC boost converter comprising:
a current transformer having first and second primaries;
a boost inductor having a first end connected to a first AC input terminal and a second end connected to a first junction defined between the anode of a first diode and a first end of said first primary, the second end of the first primary being connected to a first terminal of a first switch;
a second terminal of the first switch connected to a common line;
a parallel circuit of a capacitance and a load connected between the cathode of the first diode and the common line;
a series circuit of a second diode, said second primary and a second switch connected between the cathode of the first diode and the common line; and
a second AC input terminal connected to a second junction defined between the second primary and the second switch.
2. A bridgeless PFC boost converter according to claim 1 , further comprising a second boost inductor connected between said second AC input terminal and said second junction.
3. A bridgeless PFC boost converter according to claim 1 , wherein said first and second switches are MOSFETs.
4. A bridgeless PFC boost converter according to claim 3 , wherein said first and second switches are MOSFETs, each having a respective body diode whose cathode is connected to the corresponding one of said first and second primaries.
5. A bridgeless PFC boost converter according to claim 4 , wherein said MOSFETs each have a pair of main terminals connected respectively to said common line and to the corresponding one of said first and second primaries; and a gate terminal for controlling the MOSFET.
6. A bridgeless PFC boost converter according to claim 1 , wherein said current transformer has first and second secondaries, respective second ends of said first and second secondaries being connected together at a third junction; and
a rectifying circuit connected to said secondaries.
7. A bridgeless PFC boost converter according to claim 6 , wherein said rectifying circuit comprises:
a series connection of a resistor and a third switch being connected to said third junction;
a junction between said resistor and said third switch being connected to said common line;
a pair of zener diodes having their cathodes connected together and their anodes connected respectively to said second ends of said first and second secondaries; and
a pair of diodes having their cathodes connected to said third switch and their anodes connected respectively to said first ends of said first and second secondaries.
8. A bridgeless PFC boost converter according to claim 7 , wherein said third switch is a MOSFET.
9. A bridgeless PFC boost converter according to claim 8 , wherein said third switch is a MOSFET having a pair of main terminals connected respectively to said resistor and to said cathodes of said pair of diodes, and a gate terminal for controlling the MOSFET.