In a switched-mode power supply (SMPS), the AC mains input is directly rectified and then filtered to obtain a DC voltage. The resulting DC voltage is then switched at a high frequency (typically 10 kHz — 1 MHz), by electronic switching circuitry, thus producing an AC current that will pass through a high-frequency transformer or inductor. Higher switching frequencies enable the use of transformers and filter capacitors that are much smaller, lighter, and less expensive. After the inductor or transformer secondary, the high frequency AC is rectified and filtered to produce the stabilised DC output voltage. Depending on the power range, input voltage range, output voltages, space constraints and efficiency goals of the power supply, different topologies will provide the better trade-off.
ST’s key products for AC – DC converters are:-