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power supply for GSM sim900

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ash124

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hi every one !
i have to make power supply for gsm sim 900, and i have tried this with lm2576 regulator, but i failed...i have used the basic power supply design for lm2576
http://e2e.ti.com/support/power_management/simple_switcher/f/858/p/255499/1039477.aspx#1039477 but at the output i dont get 5 volts, i get the output voltage equal to input... i dont have IN 5822, any schottkey diode so i am using simple diode , and inductor of some different value, so i
guess becoz of these two i dont get the desired output,, am i ri8??can i use simple diode or zener diode instead of schotkey, plz help me out in this
 

What you're saying simple diode?
Send a schematic your design.
 
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    ash124

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i am using this schematic
lm2576.png
i have made the the circuit on breadboard just according to this figure and i havn't put the IN5822 diode in my circuit and i also dont know the value of the inductor which i have used in my circuit ,and i guess because of these two facts i am not able to get the correct result i-e 5v and 2A, will you please help me out in this
and by simple diode mean any of the following
Res-2.7K-1W
ZDi-8.2V
ZDi-12V
ZDi-15V
ZDi-27V
ZDi-24V
ZDi-22V
ZDi-6.8V
ZDi-10V
ZDi-9V
ZDi-3.3V
ZDi-3.3V
ZDi-3.9V
ZDi-8.2V
ZDi-7.5V
ZDi-4.7V
ZDi-5.6V
ZDi-6V
CDi-4148
Di-1N5399
Di-6AIO
Di-1N5819
Di-1N5408
Di-DIAC
Click to expand...
 
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Diode for LM2576 MUST by
schottky or Fast Recovery for current min 2.5A.
For example 1N5820 - 1N5822, MBR320P-MBR360 , SR302-SR306
Clearly can NOT be used Zener Diodes, Diac or smal signal diode as 4148
 

hi carpanter now i have implemented the circuit as shown in this figure , and used all the components which are use over here but still i dont get the correct output voltage i-e 5v
lm2576.png
can u plz help me out in this??
 

Two key questions
- What voltage is input the LM2576?
- Which version of the LM2576 you?
Figure you sent is LM2576-5 and that can only 5V.
You must have LM2576-Adj. and the FB input must be resistive divider
The resistive divider must divide the voltage Vout to the input FB was 1,23V.
For example see picture
LM2576.png


Her is simple calculator for calculating resistive divider at LM2576
 

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