I want to use this boost IC to drive an LED string.
I have 9 LEDs. 300mA forward current and 3V as typical Vf.
Can someone guide me on how to set the output voltage of the LED string using that IC?
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1 Answer
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6
You don't set the voltage.
It is an LED driver. You set the current, and the voltage takes care of itself.
Set the current using \$R_{VFB}\$ as described in equation 5. For 300mA, it looks like you'll need a one ohm resistor.
As long as the sum of the forward voltage for all of your LEDs in series is less than 60V, it'll work.
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\$\begingroup\$ Thank you very much for the answer. But a couple of questions which might be a little related to this. 1. How did you deduce that we don't have to set the voltage? Is it given or mentioned in the datasheet or do we get to know by experience? 2.How does the actual voltage take care of itself if we just set the current? \$\endgroup\$– user220456Feb 16, 2021 at 15:56
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\$\begingroup\$ 1. It's an LED driver. Current regulation is the correct thing to do. 2. Many people think "I put X volts across a diode and Y current will flow. " The reality is that you provide "Y" current and "X" voltage appears across the diode. Your "3 volts and 300 mA" rating doesn't mean "apply 3V and 300mA will flow." It means "provide 300mA, and the voltage across the device will be 3V." \$\endgroup\$– JREFeb 16, 2021 at 16:03
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\$\begingroup\$ Thank you very much for the clarification. \$\endgroup\$– user220456Feb 16, 2021 at 16:18
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\$\begingroup\$ Could you please tell me what equation you used to get the RVFB as 1 ohm and what to do with the OVFB pin? \$\endgroup\$– user220456Feb 17, 2021 at 4:21
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\$\begingroup\$ I assumed full brightness (\$V_{ADIM}>1.2V\$) and used \$I = \frac {300mV}{R_{VFB}}\$ . You connect the \$OVFB\$ pin to the junction of \$R_{OVFBH}\$ and \$R_{OVFBL}\$ as indicated in the schematic. \$\endgroup\$– JREFeb 17, 2021 at 6:42