This technology is prevalent in power supply systems for telecommunications and data center apparatus. The central element of the ACFC is a transformer (Figure 1). The main winding of the transformer receives the input voltage, resulting in the induction of a voltage in the secondary winding. The output voltage of the transformer is determined by its turn ratio. The active-clamp circuit, which incorporates supplementary semiconductor switches and a capacitor, regulates and governs the energy contained inside the leakage inductance of the transformer. When the primary switch is off, the energy stored
in the leakage inductance is redirected to the clamp capacitor, thereby preventing voltage spikes. This practice mitigates the strain on the primary switch and enhances operational effectiveness. The voltage from the transformer’s secondary winding is rectified by a diode, and the output voltage is smoothed by an output filter capacitor. Finally, ACFC operates with soft switching, meaning that switching transitions are smoother and produce less noise. This results in reduced electromagnetic interference (EMI) and lower switching losses. The ACFC circuit reduces voltage spikes and stress on components, leading to improved efficiency, especially at high input-to-output
voltage ratios. Moreover, it can handle a wide range of input voltages, making it suitable for telecom and data center applications with varying input voltages. Disadvantages of the active clamp circuit include the following: ■ If not constrained to a maximum value, an increased duty cycle can result in transformer saturation or additional voltage stress on the main switch, necessitating the precise sizing of the clamp capacitor. ■ ACFC is a single-stage DC-to- DC converter. As the power level rises, the advantages of a multiphase design for power intensive applications such as telecom will increase.
Figure 1: The ACFC topology. (Source: Analog Devices)
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