Design Of A Digitally Controlled Flyback Constant Current AC-DC Converter Chip

LED is called green light source, which has following advantages: beneficial to theenvironment、durable、and small volume. But there are significant differences betweenled illumination and incandescent Lamps. LED must have special driver because it mustworks under constant current. According to present problems, such as short life, highreliability, high cost, low precision, much research work on flyback switching power isdone in this paper. A new digital control scheme has been proposed which has beenproven effective in digital switching power supply chip XD1301.The flyback topology is adopted by XD1301, which can eliminate theopticalcoupler,TL431and other relating electronic components, so it can reduce thesize of the driver and improving reliability; The max power output is20W which can bemodified by the external circuit, so XD1301can be used in multiple LED driversolutions. Pulse by pulse wavefrom analysis allows for a accurate current control, it isas high as±1%. The reliability of the diver is greatly improved by a number of keybuilt-in protection features, such as the output shortcircuit protection, under-voltageprotection, current sense short protection, voltage sense resistor open protection, OTP,reset time too long protection; Valley mode swiching technology makes the EMI designsimpler and makes the sonversion efficiency as high as80%; built-in soft start circuitscan eliminate the surge current and avoid the output voltage overshoot.The design and verification is accomplished on the mixed-signal design platformof Cadence. The chip XD1301referred in this paper has been successfully fabricated by0.18um technology just one time. Experimental results show that this chip hasimplemented all the functions of the system design requested, and it has advantage inprecision and cost over the analogue LED driver chip. The chip XD1301fills thedomestic of digital AC-DC LED deriver chip in China.