LM2576 ADJ buck converter

ejazbeyond · Feb 27, 2019

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.

ChrisP58 · Feb 28, 2019

I suggest using TI's WEBENCH® Designer on this page:
https://www.ti.com/sitesearch/docs/...rchTerm=lm2576#q=lm2576&t=everything&linkId=1

It will give you recommended values for all components for the design.

Be aware, the LM2576 is a switching converter, NOT a linear regulator. It works by turning the output on an off rapidly. To properly work, it needs an inductor, a freewheeling diode and an output capacitor.

ejazbeyond · Feb 28, 2019

ChrisP58 said:
I suggest using TI's WEBENCH® Designer on this page:
https://www.ti.com/sitesearch/docs/...rchTerm=lm2576#q=lm2576&t=everything&linkId=1

It will give you recommended values for all components for the design.

Be aware, the LM2576 is a switching converter, NOT a linear regulator. It works by turning the output on an off rapidly. To properly work, it needs an inductor, a freewheeling diode and an output capacitor.

Thanks Chris

crutschow · Feb 28, 2019

ejazbeyond said:
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?

ejazbeyond · Feb 28, 2019

crutschow said:
It likely won't work properly without all the components connected.
Why would you think it would?

because dont have all the component, also i think other components are for smoothing purpose. my bad.

ejazbeyond · Mar 1, 2019

ejazbeyond said:
Thanks Chris

to change voltage i just need to change resistor value am i correct?
my existing circuit give me 4.48v now i need 4.18-4.2v max.

ChrisP58 · Mar 1, 2019

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.

eTech · Mar 1, 2019

Hello,

This is a LTspice sim. The component values were taken from a Winbench design, 12V in, 4.2v@3A out

eT

dr pepper · Mar 5, 2019

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.

ejazbeyond · Mar 14, 2019

thanx for your inputs. with help of webbench tool i got the values of all component. tested on hardware working fine.

hesam_m · Aug 1, 2019

You can try to build this

LM2576 ADJ buck converter

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