230 Vac Off-line Triac Dimmer Retrofit with 6 LEDs Reference Design (LM3445-REF)
The main purpose of the power supply is to convert the rectified AC Input to DC regulated current for 6 LEDs. The power supply provides protection for the LEDs, limits the transient input voltage and protect against inrush current at plug in. The overall power supply conformity (e.g. mains harmonics (EN), mains interference, international safety standards etc.) are not approved for all the applicable European Norms (EN). The principle of this power supply is a step down. It is regulated by the 350ma average current with a fixed Toff time. At the heart of the power supply is the controller LM3445 current mode control from National Semiconductor. The LM3445 switching frequency is set at a nominal 45 kHz. With the LM3445 National Semiconductor provides a device that avoids visible flickering caused by a TRIAC forward or reverse phase dimmer. The LM3445 overcomes this challenge by translating the TRIAC-chopped waveform to a DIM signal and decoding it to a DC signal. In fact, the LED current is linearly regulated according to the dimming signal.
Input Range Output LM3445 Min 180 VAC ~ 19V Max 265 VAC 350 mA The performance of the reference design is as follows: Triac dim decoder circuit for LED dimming Adjustable switching frequency Low quiescent current Triac dim decoder circuit for LED dimming Adaptive programmable off-time allows for constant ripple current Thermal shutdown No 100Hz flicker Patent pending drive architecture
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