LM3431 work with SEPIC

Kai Hsiao

Guru 12675 points

Other Parts Discussed in Thread: LM3431

Dear Sir

I will use OSRAM P2720 700mA LED (Vf=3V)

If we use 1pcs LED per channel (total 3 channel) and Vin range is 6V~36V

how to design this SPEC with SEPIC structure??

Thanks

over 7 years ago

0 Clinton Jensen over 7 years ago

TI__Mastermind 25500 points

It can do a SEPIC topology. Refer to the external link for an example with calculations:

0 Kai Hsiao over 7 years ago in reply to Clinton Jensen

Guru 12675 points

Dear Jensen

Thanks for your reply
But I only use 1pcs LED so the Vout=3V ,so LM3431 can't do Vin=6V~36V to Vout=3V/1.4A ,is it right

Thanks

0 Clinton Jensen over 7 years ago in reply to Kai Hsiao

TI__Mastermind 25500 points

The switch voltage would be 39V when the input voltage is 36V, but since it is a controller you can pick a FET with a higher voltage rating. It should be able to do 3V output with that input voltage range. You may want to use a lower switching frequency, maybe 250kHz to 350kHz, to make sure you have a low minimum duty cycle for 36V input.

0 Kai Hsiao over 7 years ago in reply to Clinton Jensen

Guru 12675 points

Dear Jensen

Do you have LM3431 reference design schematic for Vin=6V~36V to Vout=3V/1.4A ??
or other part number have similar reference design schematic ??

Thanks

0 Clinton Jensen over 7 years ago in reply to Kai Hsiao

TI__Mastermind 25500 points

The only designs available I am aware of are on ti.com and the LM3431 is the only 3 channel we have. Could you drive them in series or do the 3 LEDs need independent control? In any case the reference design I posted a link for earlier should work fine, or be at least very close to what you need, for your specifications. You may just have to adjust the output current for each string.

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LM3431 work with SEPIC