using lm2576 with 12v 5amp adapter

[devil6600]

hi

can i use lm2576 with 12v 5amp adapter? will it get burned? i want to use it for powering sim900 module

thanks

 

[IanP]

SIM900 needs 3.5-4.5V, so you have to use the LM2576ADJ to set the output voltage within that range ..
It should work fine with 12V/5A power source ..
See:
**broken link removed**

:wink:
IanP

 

[devil6600]

thanks IanP, very helpful information...
if i want to power it with 3.7v li-ion battery then should i connect it directly to the module or use a ldo regulator in between?
thanks

 

[IanP]

As the module needs 3.5V-4.5V inserting a LDO between a 3.7V-battery and the module would not give you any advantage but a small voltage drop that you don't want ..
I'd connect it directly ..

:wink:
IanP

 

[devil6600]

thanks IanP...
i was looking at the datasheet of lm2576 and found it require a schottkey diode of 3amp, i don't have it so if i skip the diode in the circuit (since its already reversed biased) then will the circuit have any major issues?

thanks

 

[Orson Cart]

the diode and the output inductor are major parts of the circuit as it is a SWITCHING regulator NOT a linear one

All the parts in fig2 are essential - Regards, Orson Cart.

 

[Wafeeq]

You Can connect SIM300DZ directly to any 3.7-4.4V Battery and it would work fine. and if you want to use Adopter of 12V output then connect a LM7805 and and series diode at the output of the 7805 for drop the volts. connect your GSM modem at the output of the diode. it will work fine.

 

[devil6600]

nice tip..
btw sim900 requires 2amp current for tx so the diode should have a 2amp current rating or a normal will do? if i connect 1n4148 then will it work?

 

[Wafeeq]

nice tip..
btw sim900 requires 2amp current for tx so the diode should have a 2amp current rating or a normal will do? if i connect 1n4148 then will it work?

LM7805 is also of 1 Ampere and i used 1n4001 diode ... Maximum surge current of Sim is 2 Ampere but i didnt see any time from my last 2 years of GSM system design experience it doesnt take more than 500mA even if call is being generated or SMS received or GPRS active mode. i used to use this same circuit for these all applications. 2575 is very good. but littly tricky circuit. you need good diode, coil and cappacitor for filtering as this gives pulses at output if there is not good filter at the end. ..

there is another option use LM317 as it is of 3 Amperes, use resistors combination to get 4.2 V directrly from it. it doesnt require any diode..

 

[devil6600]

there is another option use LM317 as it is of 3 Amperes, use resistors combination to get 4.2 V directrly from it. it doesnt require any diode..

if i use LM317 then sometimes sim900 automatically gets switched off after network registration...
anyway i have made up my mind to use LM2576..

 

[Wafeeq]

LM317's output volts must not increase than 4.45, mostly GSM modem gets restart due to over voltage shutdown. Keep output of 317 less than 4.2V..