Primary side control LED driver power supply circuit design with TRIAC dimming

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Overview:
LEDs are the fourth generation of illumination due to their high brightness, energy saving and long life. Energy-saving LED dimming is one of the hotspots of current application and research. At present, the main dimming methods for LED lighting are: analog dimming, pulse width modulation (PWM) dimming, and thyristor (TRIAC) dimming. The thyristor dimming is a commonly used dimming method because it does not need to change the original line.
Non-isolated LED drivers for TRIAC dimming add a capacitor network to the circuit to increase the holding current to ensure that the TRIAC operates in a linear period to avoid flicker problems. However, this method is only applicable to half-bridge structures and requires additional circuitry to detect the dimming angle of the TRIAC. For feedforward control schemes for flyback PFC converters with TRIAC dimming LED driver applications with isolated outputs, the output current is controlled by input power, but the output current accuracy is limited. Because TRIAC is compatible with LEDs, most industry solutions are inefficient (trigger angle detection and TRIAC sustain current require virtual load), complex isolation feedback structure or high cost of two-stage conversion, so for simple high performance and suitable for TRIAC Dimmed LED drivers are still necessary.
This paper designs a single-stage flyback converter with primary side control, which is suitable for TRIAC dimming and compatible with LED driver. The output current is accurately calculated and controlled by the primary side detection signal. Operating the converter in DCM mode, the input current will follow the input voltage to achieve a high power factor, making the LED driver well compatible with the TRIAC dimmer. In addition, the primary side control is used to make the output current signal and the TRIAC dimming signal available on the primary side, simplifying circuit functions. The output current is changed by the change in the TRIAC conduction angle, resulting in a nearly linear dimming curve.
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