I want to connect a Li-Ion battery on a GSM/GPRS module expecially this one (http://www.electrodragon.com/w/GSM_GPRS_A6_Module). In general parameters is mentioned operating voltage from 3.3V to 4.2V A simple Li-Ion battery when is fully charged goes up to 4.2V, somethings slightly above this. The question is, how can I protect the GPRS module from this fully charged battery's voltage? I'm looking for something efficient...
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\$\begingroup\$ A typical Li-Po cell (charge level 4.35V) seldom has its output above 4.2 V after few minutes of end of charge, and under a small load, and most working voltage will be below 4 V, in 3.7V range. In case of this particular GSM/GPRS module I would worry more to keep the supply voltage at recommended "4 V", and keep it above 3.4V. \$\endgroup\$– Ale..chenskiJul 14, 2017 at 18:28
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\$\begingroup\$ Also, if the "operating voltage" is 4.2 V, then few minutes of 4.4-4.5 V would do no harm to the module, since the operating voltage ("safe voltage") for silicon chips and modules usually has 5-10% guard. \$\endgroup\$– Ale..chenskiJul 14, 2017 at 18:50
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\$\begingroup\$ Yes I'll second that. But, I'm planning to use the battery directly during it being charged, directly from its charger. For example, using this battery charger ti.com/product/bq24295 \$\endgroup\$– MrBitJul 14, 2017 at 18:51
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\$\begingroup\$ The BQ24295 is not just a charger, it is a pretty sophisticated power management IC (PMIC). Yes, it is designed for this kind of applications. You might need to do some adjustments however over I2C bus. \$\endgroup\$– Ale..chenskiJul 14, 2017 at 21:20
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2 Answers
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All GSM/GPRS/LTE module I've worked with are fine when supplied from a single li-ion cell. As you see the range is from 3,3 to 4,2V. Li-ion cells never (should) get above this voltage, so you are okay to power it directly from a li-ion cell.
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From the GSM module voltage specification, it sounds like it was made for a single cell Li-ion battery, with 4.2V max and 3.3V minimum for that logic level. I would be willing to bet that the module has some internal voltage regulation that is going to be able to accept 4.2V and even a bit above and bring it down closer to the 3.3V at which it is likely working. One suggestion: try to find that voltage regulation on the GSM module and, if possible, get a sense of how hot it is running. If it is getting so hot that you could not keep your finger on it, then you might consider putting on a small heatsink to help it with the voltage regulation when the battery is fully charged.