Led lighting circuit

An LED lighting circuit which controls current flowing in a transformer unit by performing PWM control based on feedback of a final output voltage applied to LEDs, and after rectifying the voltage on the secondary side of the transformer unit, smoothens a power supply and blocks surges through an output-side smoothing and surge protection unit to supply to the LEDs, comprising:

• a microcomputer alternately generating a high signal and a low signal, which are different outputs, at a third output pin and a fourth output pin each time IC power is applied;
• a third switching unit in which a third switching element, FET, is turned on when the third output pin of the microcomputer is the high signal to allow power to be smoothed by smoothing capacitors, and the FET is turned off when the third output pin is the low signal to clamp transient voltage inflowing into a transient voltage suppressor (TVS3);
• and
• a fourth switching unit in which a fourth switching element, FET, is turned on when the fourth output pin of the microcomputer is the high signal to allow power to be smoothed by the smoothing capacitors, and the FET is turned off when the fourth output pin is the low signal to clamp the transient voltage through a transient voltage suppressor (TVS4).