Electronic – LM317 vs series diode (1N4007) as voltage regulator

diodeslm317voltage-regulator

I am using the SIM900A GSM module which requires 3.2V to 4.8V with max current draw of 2A.

In my board, I have a 5V, 3A supply which will be used to power the SIM900A.

Generally, in my search I found 2 ways to power it:

  1. Use a LM317 regulator to produce around 3.9-4V
  2. Just simply use a high current series diode (like the 1N4007, with forward voltage = 0.6v) to produce 5V-0.6V = 4.4V

My question is Is there any advantage of 1 over 2 (or disadvantage of 2 over 1 for that matter) as 2. is much simpler and cheaper.

I want to use 2 if there shouldn't be any major disadvantage.

I have seen both in commercial Chinese SIM900A modules, so I guess there should not be any problem with 2. But then why use the LM317?

Thanks.

Best Answer

The simple series diode is just fine IF you can guarantee that the input voltage will never exceed 5.2 Vdc.

The LM317 regulator has the advantage that it will protect the GSM module if the input voltage is excessive.

For example, if someone connected the power supply to 12 Vdc instead of 5V, the LM317 regulator would simply get very hot, then shut down because of the internal thermal protection. This would save your (expensive) GSM module from being damaged.

Either method is fine.

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