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Voltage regulator reading high

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camerart

Active Member
Hi,
I've just built a PCB, with 2x 3.3v voltage regulators. Both of them are reading 4.2V.

This has happened before, but I can't remember what I did to fix it. Does anyone have any ideas please?

Camerart.
 

camerart

Active Member
Hi N and K,

I have previous circuits wired the same way.
I tried removing the caps and replacing them 4.2v both times.
There are two REGs on the PCB.
There is a PIC connected. to one of them, both still 4.2V
C.
 

camerart

Active Member
Hi,
I've found the problem!

I looked more closely at e numbers on the regulators, and the offending ones are ON RFE 17L50 where previously I've used ON RGH 17-33 I've changed them and now they both read 3.3V

Does anyone have a data sheet for ON RFE 17L50 please, I think they must have a different pin out arrangement. WHY !!!:banghead:

Thanks, C.
 

tomizett

Active Member
Can't find any datasheets matching 17L50.... does sound like it could be a 5V though.
Regarding pinning, however, you'll find that some regulators - even in the same package - do have different pinning. The difference (in my experience) is between "standard" dropout regulators, which use an NPN pass transistor, and "low" dropout regulators, which use a PNP pass transistor. I presume it's to do with which terminal of the pass transistor needs to be bonded to the thermal tab - although that said, in a standard +ve regulator the tab is ground, which is not one of the pass element's terminals at all...

So the moral of the story is to check the pinouts for the exact device you're using - take it from someone who cam close to being caught out by this recently!
 

camerart

Active Member
Hi N and T,

I'm sure your correct and they are 5V regs (5V Battery = 4.2V). (Just had another look at the component tube and sure enough they're marked 5V AND! I've drawn the pinouts on the tube, which are the same)

Cheers, Camerart.
 
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