A single-phase active-clamped (AC) flyback converter is a type of power electronic circuit used to convert DC (direct current) voltage into AC (alternating current) voltage, often with isolation between input and output. It is commonly used in applications such as power supplies, battery chargers, and renewable energy systems. The active-clamped topology is employed to improve efficiency and reduce voltage stress on the components, particularly the switching devices.
Here's how a single-phase active-clamped flyback converter operates:
Input Stage:
The converter begins with a DC input voltage, typically obtained from a rectified AC source or a battery.
The input voltage is controlled by a power switch (usually a MOSFET or IGBT) which is turned on and off at a high frequency using a pulse-width modulation (PWM) signal. This switching action allows energy to be transferred from the input to the output.
Primary Side Operation:
When the power switch is turned on, current flows through the primary winding of the transformer. Energy is stored in the transformer's magnetic field.
During this time, the primary side diode (often a fast-recovery diode) is reverse-biased and remains off.
Clamping Action:
As the power switch turns off, the primary-side voltage spikes due to the energy stored in the transformer's magnetic field. These voltage spikes can stress the components and reduce efficiency.
To mitigate these voltage spikes, an active clamp circuit comes into play. This circuit consists of another switch (clamp switch) and a clamp capacitor. The clamp switch is typically a fast-switching diode or an active switch like a MOSFET.
Before the primary side voltage spike can reach a critical level, the clamp switch is turned on. This action creates a closed loop for the voltage, allowing the excessive energy to be absorbed by the clamp capacitor and shared between the primary winding and the clamp capacitor.
Secondary Side Operation:
The transformer's secondary winding transfers energy to the secondary side, where another rectifier diode (often a synchronous rectifier for higher efficiency) converts the AC voltage into DC.
An output filter, often comprising an LC filter (inductor and capacitor), smooths out the voltage ripple and delivers a relatively stable DC voltage to the load.
Control and Regulation:
A control circuit, often implemented using a controller IC or microcontroller, senses the output voltage and adjusts the duty cycle of the primary-side switch (PWM control) to regulate the output voltage.
By actively clamping the primary-side voltage spikes, the active-clamped flyback converter reduces stress on the components, allowing for higher efficiency, lower switching losses, and improved overall performance compared to traditional flyback converters. This topology is especially beneficial for applications requiring high efficiency, wide input voltage range, and galvanic isolation between input and output.