[SOLVED] LM 317 for SIM900 will it work? .... need some suggetions

[FvM]

The combination of diode and LM317 doesn't seem to serve a reasonable purpose. If your input voltage is constant 5V, a diode circuit instead of a regulator may be considered as poor man's voltage dropper. If there's any doubt about the input voltage staying within safe limits, you need a 2A rated regulator. Or a respective large output capacitor.

 

[betwixt]

Either you have re-invented physics or your 1N5408 is faulty.

The LM317 does precisely nothing and can be removed without any change to output voltage. Reason: To regulate, the LM317 needs at least 1.5V more on it's input pin (and preferably more) than it's output pin. The diode limits the maximum possible to about 0.7V difference so the LM317 will not operate, all the current flows through the diode. Connecting the output and ADJ pins will not work. It's like connecting your car road wheel to it's steering wheel and expecting to drive in a straight line.

Try this: Remove the LM317, keep the diode and the capacitor(C2) after it. Also wire a 1K resistor across the capacitor to keep a small trickle current flowing through the diode, it will help to stabilize the voltage.

Brian.

 

[SiddharthGajjar]

my input voltage from battery is 5.0 DC that's why i am little worried that how to produce regulate 4.4 voltage without resistor network(which can vary due to change in temperature).

 

[KlausST]

Hi,

my input voltage from battery is 5.0 DC

I doubt the battery voltage to be 5.0V (What chemistry?)
And I doubt the battery voltage is stable.
-->it will vary with load current and it will vary with charge level.

that's why i am little worried that how to produce regulate 4.4 voltage without resistor network

All the answers were given in the posts before.
Follow them...or not

Klaus

 

[SiddharthGajjar]

used 1n5408 diode with 1000uF capacitor and 1k Resistor across it.....
and guess i got the best result... output voltage of 4.48 VDC. it can feed burst current to Sim900A as well.

no garbage and each command accepted in first.

 

[hobbyckts]

No, All the suggestions for you from starting stage is not to use the LM317 regulator. It will not serve you the best result, Because the difference between the input & output voltages and the burst current required for SIM900A. LM317 is unable to do both these things. Better go for some alternative regulator which gives you the best result.

Sure this will cost so much or else if possible increase your input voltage range and go for any other regulator but not again to LM317. This may reduce your regulator cost.