Power factor correction circuit
A power factor correction circuit used for regulating the phase of a DC current outputted from a rectifier unit in a power supply includes an energy inductor, an output diode, a switch unit, a pulse width modulation unit, a sensing resistor, and a converter transformer. The converter transformer utilizes the DC current outputted from the rectifier unit to generate an induced current, which will pass through the two ends of the sensing resistor to produce a reference voltage, thereby the pulse width modulation unit can produce the duty cycle for the switch unit according to the reference voltage, so that the switch unit can regulate the phase of the DC current through controlling the flowing direction of the DC current.
1. A power factor correction (PFC) circuit used in a power supply, which comprises a rectifier unit and a power output unit, wherein the PFC circuit is connected at the back end of the rectifier unit for regulating the phase of a DC current at the back end of the rectifier unit, the PFC circuit comprising:
an energy storage inductor, for receiving the rectified DC current and storing energy and discharging;
an output diode, electrically connected between the energy storage inductor and the power output unit;
a switch unit, parallel connected at the back end of the rectifier unit;
a magnetic material;
a primary winding, series connected with the switch unit and wound on the magnetic material;
a secondary winding, wound on the magnetic material, wherein when the DC current passes through the primary winding, the secondary winding produces an induced current;
a sensing resistor, crossed at two ends of the secondary winding for producing a reference voltage when the induced current from the secondary winding passes through the two ends of the sensing resistor; and
a pulse width modulation (PWM) unit, for producing a duty cycle for the switch unit according to the reference voltage so as to regulate the phase of the DC current.
2. The power factor correction circuit as claimed in claim 1 , wherein the rectifier unit transforms an inputted AC power into the DC power.
3. The power factor correction circuit as claimed in claim 1 , wherein a main transformer is further included between the power output unit and the output diode.
4. The power factor correction circuit as claimed in claim 1 , wherein when the switch unit is closed, the DC current passes through the switch unit, and when the switch unit is opened, the DC current passes through the power output unit.
5. The power factor correction circuit as claimed in claim 1 , wherein when the switch unit is closed, the energy of the DC current is stored in the energy storage inductor.
6. The power factor correction circuit as claimed in claim 1 , wherein the magnitudes of the DC current and the induced current are in inverse proportion to the circle numbers of the primary winding and the secondary winding.
7. The power factor correction circuit as claimed in claim 1 , wherein the circle number of the secondary winding is larger than that of the primary winding, so that the induced current from the secondary winding is smaller than the DC current passing through the primary winding.
8. The power factor correction circuit as claimed in claim 1 , wherein the reference voltage is the potential difference produced by the induced current passing through the sensing resistor.