LM-2577 Step up circuit.

[gauravkothari23]

HI all,
i have got a step up circuit 5v to 12v (image attached) using lm2577 IC. can anybosy please help me to what changes should i make to get output 5v with input 3 - 3.5v.

 

[Easyrider83]

It can work with voltage range 3.5 - 40V. Not 3.0V
See adjustable version example. Page 3
https://www.ti.com/lit/ds/snos658d/snos658d.pdf

 

[hobbyckts]

Input should be Greater or equal to 3.5V and not 3V

 

[gauravkothari23]

Input should be Greater or equal to 3.5V and not 3V

Thanks a lot....
ok... then what if the input is from the range 3.5v to 4.2v. i would use li-poly/ion battery.
what changes should i need to do to get a 5v output....

 

[Easyrider83]

I can't get your problem with manual reading. The formula for Vout is: Vout = 1.23 (1 + R2/R1). So, basicaly, you only need to calculate R1 and R2.

 

[hobbyckts]

Use Adjustable version of LM2577. i.e. LM2577-Adj.

Then use a voltage divider circuit which is connected in between Vout and ground. The voltage divider must be connected to feedback pin.

The Output voltage is given by as per data sheet is Vout = 1.23 (1+R1/R2). So the ratio of R1/R2 resistor value should be 3.06 to get the output voltage of 5V.

 

[dante_clericuzzio]

HI all,
i have got a step up circuit 5v to 12v (image attached) using lm2577 IC. can anybosy please help me to what changes should i make to get output 5v with input 3 - 3.5v.

I have this video demonstration