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Enable external PWM dimmong on LM3445 230VAC, 8W Isolated Flyback LED Driver Demo Board (Part number: LM3445-230VFLBK)

Albert Lee2
Prodigy 30 points
Other Parts Discussed in Thread: LM3445

Dear all,

I wonder if anybody has ever used the LM3445 AC-DC LED Driver board. I have the following specific questions on how to enable external PWM dimming on the LM3445 230VAC, 8W Isolated Flyback LED Driver Demo Board (Part number: LM3445-230VFLBK). 

1. Without changing the circuits in the demo board, can I just feed in an external PWM signal (3.3V for logic high and 0V for logic low) directly into the DIM pin (pin #3) of LM3445 ?

2. What should be the ground reference for this external PWM signal ?  Should it be referenced to PGND (Primary Side Ground) -or- SGND (Secondary Side Ground) ?  There are two grounds in this AC-DC LED Driver and I am not sure which ground should this external PWM signal be referenced to.

3. For no dimming (i.e. duty ratio of 100%), should I feed in a constant DC voltage of 3.3 V to this DIM pin (pin #3) of LM3445 ?  -Or- should I feed in a constant DC voltage of zero volts to it ?   It appears that the datasheet does not mention about this specifically. 

I really appreciate if someone can help...

Thanks.

Sincerely,
Albert