A single-phase active-clamped (AC) flyback power factor correction (PFC) converter is a type of power electronics circuit used to improve the power factor and efficiency of power supplies, especially in applications where a single-phase AC input is available. The converter combines the features of a flyback converter and an active clamp circuit to achieve power factor correction.
Here's a general description of the operation of a single-phase active-clamped flyback PFC converter:
Input Rectification: The single-phase AC input voltage is first rectified using a diode bridge, converting the AC voltage into a pulsating DC voltage. The output of the diode bridge is typically a high-voltage DC, which is then fed to the PFC stage.
PFC Stage: The PFC stage is responsible for correcting the power factor of the input current to make it more sinusoidal and in phase with the input voltage. This is achieved using active power factor correction techniques, typically employing a boost converter topology. The boost converter operates in continuous conduction mode (CCM) to regulate the output voltage and draw current from the AC source in a controlled manner. By controlling the duty cycle of the boost converter, the converter shapes the input current waveform to be in sync with the input voltage, thus improving the power factor.
Flyback Stage: After the power factor correction stage, the regulated high-voltage DC is fed into the flyback converter stage. The flyback converter is a type of isolated DC-DC converter that steps down the high-voltage DC to a lower voltage suitable for the load.
Active Clamp Circuit: In a standard flyback converter, there is a transformer that provides isolation between the input and output. When the primary switch (typically a MOSFET) turns off, the energy stored in the transformer's primary winding causes voltage spikes due to parasitic elements. These spikes can damage the switches and other components. To mitigate this issue, an active clamp circuit is used.
Operation of Active Clamp: The active clamp circuit consists of an auxiliary switch (often another MOSFET), a clamp capacitor, and a diode. When the main switch turns off, the clamp capacitor is charged through the auxiliary switch, providing a path for the energy stored in the transformer's primary winding. This action limits the voltage spikes and reduces stress on the main switch.
Output Regulation: The flyback converter's secondary winding provides the isolated output voltage, which is rectified and filtered to obtain a stable DC output voltage. The output voltage is regulated by controlling the duty cycle of the main switch, maintaining a constant output voltage despite changes in load conditions.
By combining the active-clamp circuit with the flyback converter and integrating power factor correction techniques, the single-phase active-clamped flyback PFC converter achieves higher efficiency, better power factor, and improved performance compared to conventional flyback converters without PFC. It is commonly used in applications where power factor correction and isolation are required, such as in low-to-medium power AC-DC power supplies for electronic devices and appliances.