High Frequency Primary Side Power Switcher for Off-line SMPS
Created: Sep 26, 2016
No description available.
Nowadays, consumer electronics market and LED drive market have been rapidly developing. In regards with these markets, size, cost and power consumption are the primary considerations in the design. Many power supplies utilize flyback topology and secondary feedback for output regulation. However, these methods can’t reduce the cost and size of the device. This leads to Primary Side Regulation (PSR), which provides low power consumption, high efficiency and low cost power supply. This design is intended for off-line SMPS. In off-line converters, the AC voltage is rectified to DC directly off the AC power line and filtered with no isolation transformer and then processed with a DC-DC converter that provides isolation at the switching frequency.
This reference design features AP3983 off-line, switching controller that is designed to cut costs and improve power supply performance in consumer electronics products. The AP3983 switcher regulates output voltage using piece-wide Pulse Frequency Modulation (p-PFM) in Discontinuous Conduction Mode (DCM). Analog levels are represented as fixed-duration pulses of varying repetition rate. It has also a built-in MOSFET with 650 BVDSS and low start-up current of 200nA. The AP3983 captures the auxiliary winding feedback voltage at FB pin and operates in constant-voltage (CV) mode to regulate the output voltage. When the power switch is turned on, a turn-on spike on the output pulse rising edge will occur on the sense-resistor. To avoid false termination of the switching pulse, a typical 500ns leading edge blanking is built in. During this blanking period, the current sense comparator is disabled and the gate driver cannot be switched off. The AP3983 has built-in fixed voltage of 0.3V typical to compensate the drop of output cable when the load is changed from zero to full load. A typical 10nF external capacitor connected to the CPC pin is used to smooth voltage signal for cable compensation.
This design is intended to be used in consumer electronics products which include charger, adapter for ADSL, home appliance power supply, LED lighting power supply and PC auxiliary power supplies. Additional benefits of the design include improved output voltage and current accuracy, enhanced over-voltage and short-circuit protection, and better EMC performance, achieved by frequency dithering.