I need a powersupply for a radio board (I will shield it), and have experienced bad interference from step-down converters. I have been told to use linear regulators (LM317 or LM350) with caps to trim the current. Am I correctly informed?

I have several boards, one to receive and one to transmit. Both take 4-6V in, and consume no more than 300mA. I've also found USB supplies (both battery, charger and laptop) to be very noisy, compared to just 3 AA batteries in series. Probably because they are backed by some sort of switching power supply hooey.

Cluebatter up!;)

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    $\begingroup$ To help you with this question, you should specify the voltage and current that your circuit requires. $\endgroup$ – Glenn W9IQ May 8 '17 at 0:44

I would suggest an LM7805 type regulator. It will put out 5 volts for up to one amp current draw. You will need a filtered DC power source of 7 to 12 volts and a heatsink for the regulator. The 7805 regulator is quite common and very inexpensive.

This type of supply is called a linear supply. It is not as efficient as a switching type supply but you avoid the hash common with most switching supplies.

  • $\begingroup$ I have only one of those, but several 7905s. I will pay attention to using the right caps, and shield the box - should this be sufficient, or can I do more? $\endgroup$ – user2497 May 8 '17 at 0:58
  • $\begingroup$ No, the 7905 is -5V . Guess I'll buy some more 7805s, they seem useful to have. Can I get by with a few LM317s until I get more 7805s? $\endgroup$ – user2497 May 8 '17 at 1:01
  • $\begingroup$ Pay attention to the bypass capacitors in the app notes.they will help to keep the regulator stable. You can also add an RF choke to the ouput to help keep RF out of the PS. I always keep a dozen 7805s and some of the other voltage versions on hand. The shipping is more than the parts cost. $\endgroup$ – Glenn W9IQ May 8 '17 at 1:05
  • $\begingroup$ The LM317 is a good substitute. The only downsides are the extra pot and the need to adjust the circuit. The good part is they make a nice adjustable supply for future projects. $\endgroup$ – Glenn W9IQ May 8 '17 at 1:08
  • $\begingroup$ Thanks. If you have to power some projects from switching power supplies, how can you bring down the noise, generally? I have considered LM317, LM350 and ferrite beads so far, but I'm not that experienced with sensitive RF circuitry yet. $\endgroup$ – user2497 May 8 '17 at 1:10

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