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'[EE]: Voltage Regulator Trouble'
2002\07\23@144709 by Richard Mellina

picon face
       I have had trouble figuring out the problem with a 5V voltage regulator
circuit I am building. I soldered it together and at first it didn't work. I
realized it was a soldering error on my part and there was a short. I got it
working and didn't think any thing of it. The next day I test it to find
that it is not working properly. There is a very small voltage on the output
of the regulator that quickly drops to
0 when I test it. Suspecting another short I use a continuity test and find
nothing. I test it many times with no results. Then out of nowhere it starts
working again. This has got me baffled. I am wondering if it could be a
fault with the regulator itself. I am sure that none of the other circuitry
and ICs are to blame. Perhaps the regulator got to hot during soldering even
though I used a heat sink. Here is the regulator circuit:


                                 _______
                            |     |
Vin      ---+-------+----|  IC1  |----+-------  Vout
               |       |    |_______|    |
               |         |          |        |
            ---         ---         |       ---
          C1---   C2---       |       --- C3
               |         |          |        |
               +-------+--------|--------+
                                  Gnd

C1 - 100uF electrolytic cap
C2, C3 - 0.1uF tantalum
IC1 - L4940V5 low drop out voltage regulator

       The drop out voltage of the regulator is 0.5V. Any ideas on what the
problem is?

Thanks

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2002\07\23@150203 by Tal Bejerano - AMC

flavicon
face
Richard

Just disconnect all other parts. give it input voltage about 6-8V and
measure it.
If it give 5v stable then it's a good part, and look for other malfunction
parts.


Regards

Tal Bejerano
AMC - ISRAEL


{Original Message removed}

2002\07\23@163944 by rsillem

picon face
Sorry, for some reason the schematic is totally messed up.

-----Original Message-----
From: pic microcontroller discussion list
[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of Richard Mellina
Sent: Tuesday, July 23, 2002 1:42 PM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: [EE]: Voltage Regulator Trouble


       I have had trouble figuring out the problem with a 5V voltage
regulator
circuit I am building. I soldered it together and at first it didn't work. I
realized it was a soldering error on my part and there was a short. I got it
working and didn't think any thing of it. The next day I test it to find
that it is not working properly. There is a very small voltage on the output
of the regulator that quickly drops to
0 when I test it. Suspecting another short I use a continuity test and find
nothing. I test it many times with no results. Then out of nowhere it starts
working again. This has got me baffled. I am wondering if it could be a
fault with the regulator itself. I am sure that none of the other circuitry
and ICs are to blame. Perhaps the regulator got to hot during soldering even
though I used a heat sink. Here is the regulator circuit:


                                 _______
                            |     |
Vin      ---+-------+----|  IC1  |----+-------  Vout
               |       |    |_______|    |
               |         |          |        |
            ---         ---         |       ---
          C1---   C2---       |       --- C3
               |         |          |        |
               +-------+--------|--------+
                                  Gnd

C1 - 100uF electrolytic cap
C2, C3 - 0.1uF tantalum
IC1 - L4940V5 low drop out voltage regulator

       The drop out voltage of the regulator is 0.5V. Any ideas on what the
problem is?

Thanks

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2002\07\23@185626 by Kevinhoward

picon face
Try replacing the Tantalum capacitors- they may be leaky or short, especially
if they are bought surplus!


Regards

Kevin

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