Tandem voltage regulators

Newzed

If I have a 5 volt regulator supplying a 3 volt regulator and the 5 volt regulator has a 10uf cap and a .1uf cap on its output, does the 3 volt regulator need any additional filtering, other than perhaps a .1uf at the pin it is supplying?

Sid

RDL2004

Since the 3 volt regulator is merely dropping an already regulated 5 volts, there should be no need for any additional caps, though as you say a .1uf on the output can't hurt.

- Rick

Mike Cook

Sid,

Just to make sure, check the data sheet for the regulator you are using.

I'm using a LM2937ET-3.3 regulator on my HBPDB (Home Brew Propeller Demo Board) and the regulator's data sheet states:

"** Required for stability. Cout must be at least 10 µF (over the full expected operating temperature range) and located as close as possible to the regulator. The equivalent series resistance, ESR, of this capacitor may be as high as 3Ω."

When I first bread boarded this regulator circuit I did not put the cap on the output. When I measured the output voltage it was around 4.3 VDC, went back and read the data sheet, put the cap in and then it measured a rock solid 3.3VDC

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Mike

Newzed

OK, Mike.· I'll add a 10uf on the 3.3 output just to play safe.

Sid