raghavendratalekar said:if you use lm7805 u are going to spoil the sim300 module coz its rated for 4.2V max so make a simple powersupply using lm317t and use a 10k adjustable preset for varying the voltage and a 220 ohm resistor between vout and adj pins just add a good 1000uF electrolytic capacitors at the output preferrably 2nos in parallel and add a 100nF ceramic capacitor to filter the noise. use a standard LG FWT adaptor SMPS type, rated for 9VDC and 1A thats enough and works well. but before connecting the sim300 module adjust the output voltage to 4.2VDC (max typical is 4V). do not exceed this voltge rating as you will damage the sim 300, this psu will work with all simcom modules - sim 300z, sim300c, sim300d, sim 548c, sim 548, sim 600 etc.
dont worry about the 2A rating given in datasheet coz when you add the 2X1000uF caps in parallel at o/p of your supply it will buffer enough current okay!
Added after 14 minutes:
here is the schematic for your convenience. ive been using this power supply with all my simcom designs, ive used it with sim300z,c,d,340e,548c,548z,600. if you want auto power on of the module you can connect a 470uF cap with its +ve connected to the pwrkey pin and -ve connected to ground and add a 100k resistor between vbat and pwrkey i.e. pull up.
Added after 56 seconds:
GSM Man said:I use a simlar design on my power supplies, but I would recommend you use fixed resistors in place of the pot. There's no reason you should have to adjust the voltage and if the pot is accidently changed you run the risk of burning out the module.
Use 1% metal film resistors. Replace V1 with a 510 ohm resistor and you'll get an output of 4.15 volts. If you want a different output voltage, here's a link to a handy on-line calculator for determining the LM317 resistor values: https://www.muzique.com/schem/lm317.htm
input voltages.
What in the world are you talking about! You don't need a 1W resistor for the adjustment terminal, and if you did it wouldn't matter if it was a fixed reistor or pot!raghavendratalekar said:thats right using 1% resistors but buddy you would need at least 1w rating for that
jsidev said:Hi,
Better results for switching regulator with max current up to 2.5A and LiIon charger circuit with 400mA limited current output. The LDO regulators are for uc & gps module power supply. All resistors are 1% metal film. Thanks
hy
So I just connected my SIM900 with 3x Tantalum electrolytic capacitor, SMD 470 uF 6 VDC (ESR 0.065 Ω)
But still I get a voltage drop of 840mV over a time of 1.2mS from 4V to 3.2V that's too much I think but what can I change?
Thx
Andy
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