Design Of A LED Driver With Single-stage Power Factor Correction

In our daily life, AC/DC Switching Mode Power Supply(SMPS) is more and more widely used, the harmonics of SMPS creat harmonic pollution to the AC power grid. So high PF become a demand of the AC power grid to load. Power Factor Correction(PFC) technology adjusts the waveform of input current to the waveform of input voltage, in this way,we reduce the Total Harmonic Distortion(THD) efficiently and reduce the harmonic pollution to the AC power grid. With the implementation of the international standard of suppressing harmonic pollution, PFC technology is more and more widely used in AC/DC power supply field for its own merits.This paper presents a AC/DC power supply chip with single-stage PFC. The chip can achieve high power factor, triac dimming, accurate constant current output, no electrolytic capacitors and other features. The regulator module inside the chip extract current from the drain of the MOSFET integrated inside the chip, and charge the capacitor outside to supply power to the entire chip. The chip samples the output current, and it can control the duty cycle of the drive signal to achieve constant current output through PWM and PFM. The internal feedback control loop is implemented by digital circuits, thus reducing the bias error introduced by process. An internal state machine generates a pulse signal which has a frequency equals to the haif of the AC input voltage, the pulse signal is the clock signal of the state machine which controls the update time of the state machine, this makes the on-time and frequency of drive signal in half of an AC cycle don’t change, and this meets the core idea of single-stage PFC.With 220 VAC input voltage and 16 V output voltage under no dimming situation, output current of the circuit is 350 mA and the Power Factor is about 0.91. With 220 VAC input voltage and 16 V output voltage under no dimming situation, output current of the circuit is 350 mA and the Power Factor is about 0.91. With 220 VAC input voltage under jumping load situation, the chip’s dynamic response performance is also simulated and verified. With 220 VAC input voltage and under the dimming of 90 degrees, output current of the circuit is 250 mA. The simulation results show that the design meets the expected requirements.