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LM2576 ADJ buck converter

hello, i m trying to power my sim800 from a 12v dc supply, as sim800 work in 3.4-4.4v. i m using LM2576 ADJ to step down 12v to 4.2v. i have calculated value of resistor using a online calculator https://www.changpuak.ch/electronics/FeedbackCalculator.php , R1=8.2k & R2=3.3k. when i am using it on hardware its giving 5.16v instead of 4.2v. i have not connected any capacitor or diode as i just want to check voltage. Please suggest any simulation or provide proteus library for lm2576 as i am unable to find it.



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i have not connected any capacitor or diode
It likely won't work properly without all the components connected.
Why would you think it would?


Well-Known Member
Yes. The output voltage is set by the ratio of the two feedback resistors, factoring in the internal reference voltage. See the datasheet for the exact equation, or use TI's WEBENCH® Designer.

But you must have ALL of the components needed for the complete circuit.

dr pepper

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The sim circuit has a load resistor, dd you have a load resistor on the practical circuit, if not thats probably why its on the high side.

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