AC to DC power converter using an energy-storage capacitor for providing hold-up time function
An AC to DC power converter with hold up time function has a charging switch and a mode switch. The charging switch is connected between an output capacitor of a PFC controlling circuit and an energy-storage capacitor. The mode switch is connected between the energy-storage capacitor and an input of the PFC controlling circuit. The charging and mode switches are controlled by a PFC controller. When AC power is normal, the charging switch turns on and mode switch turns off. Meanwhile, the energy-storage capacitor and the output capacitor are connected in parallel to store energy in the energy-storage capacitor. When the AC power source is interrupted, the charging switch turns off and mode switch turns on. Therefore, the energy-storage capacitor is disconnected from the output capacitor. The PFC circuit obtains power from the energy-storage capacitor and continuous to supply an output voltage for a while.
1. An AC to DC power converter using an energy-storage capacitor for providing hold-up time function comprising:
a full wave rectifier receiving AC power and rectifying the AC power to sine DC power;
a power factor correction (PFC) circuit having an input terminal connected to the full wave rectifier and receiving the sine DC power and comprising an output capacitor;
a PFC controller connected to the full wave rectifier and the PFC circuit to obtain a voltage signal and a voltage of the sine DC power, adjusting a voltage phase and a current phase of the sine DC power to be consistent with each other, and regulating the sine DC power to produce a DC voltage on the output capacitor;
a switch type DC to DC converter connected to the output capacitor of the PFC circuit, and bucking the DC voltage to produce a low DC voltage;
an energy-storage capacitor connected in parallel to the output capacitor through a charging switch, the charging switch being controlled by the PFC controller; and
a mode switch connected between the energy-storage capacitor and the input terminal of the PFC circuit.
2. The AC to DC power converter as claimed in claim 1 , wherein the PFC circuit further comprising:
a switch unit connected to the full wave rectifier and comprising a first switch and a second switch being connected in series, the first switch and the second switch being controlled by the PFC controller;
an inductor having a first terminal and a second terminal, the first terminal connected to a node where the first switch and the second switch are connected in series;
a third switch connected between the second terminal of the inductor and a ground, and controlled by the PFC controller;
a diode having an anode and a cathode, the anode connected to the second terminal of the inductor, the cathode connected to the output capacitor and the charging switch.
3. The AC to DC power converter as claimed in claim 2 , wherein the first switch, the second switch, the third switch, the charging switch and the mode switch are field-effect transistors.
4. The AC to DC power converter as claimed in claim 2 , wherein when the PFC controller obtains the voltage signal and the current signal of the sine DC power, the PFC controller further compares the voltage signal with a threshold value and is operated in
a boost mode when the voltage signal is lower than the threshold value;
a buck mode when the voltage signal is higher than the threshold value; or
a hold-up time mode when the voltage signal is zero;
wherein the PFC controller in the boost mode turns on the first switch and the charging switch, turns off the second switch and the mode switch, and adjusts a duty cycle of the third switch based on a difference between the voltage signal and the threshold value for regulating the voltage signal to be consistent with the threshold value;
wherein the PFC controller in the buck mode turns on the charging switch, turns off the third switch and the mode switch, and selectively and alternately turns on and turns off the first switch or the second switch based on the difference between the voltage signal and the threshold value;
wherein the PFC controller in the hold-up time mode turns on the first switch and the mode switch, turns off the second switch and the charging switch, and adjusts a duty cycle of the third switch until energy stored in the energy-storage capacitor is insufficient.
5. The AC to DC power converter as claimed in claim 1 , wherein the first switch, the second switch, the third switch, the charging switch and the mode switch are field-effect transistors.