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I decided to make an adjustable power supply with input voltages from 3 to 6 volts (4A), and output voltages from 2 to 12 volts. But I had a thought, that as long as I'm making it, I should make it go down not just to 2 volts, but as low as possible, as close to 0V as possible.

I would also like to controll current. Currently it is controlled by the fixed Rsn resistor.

I decided to use LM3488 in SEPIC configuration.

LM3488 SEPIC

(1) How to make the output go down to 0V?

(2) How to controll current with a pot or something similar?

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The FB pin regulates to about 1.26 volts so this would be the lowest voltage normally attainable at the output but you could experiment with a bias resistor fed from an independent stable reference of (say) 2.5 volts and injecting current into the RF1 and RF2 node.

This will con the chip into thinking it is in regulation and the output voltage will be naturally lower. This may or may not work of course. Doing the same sort of trick with the ISEN pin may also prove useful in being able to alter the current limit.

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