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Author Topic: Voltage regulator problem  (Read 1244 times)

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Offline jsmokerTopic starter

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Voltage regulator problem
« on: October 13, 2008, 08:39:16 AM »
I'm using a LP2981 low drop out 5V voltage regulator along with a dsPIC30F3012 for a couple small (in size) applications and I seem to be having a powering  problem. 

For the first application I tried using 2 x 2032 button batteries (adding to ~6 volts).  For some reason this didn't work, yet when I connected it to 5.5V power supply it did work.  I had to move up to a 7.2V lithium polymer battery which was a lot bigger (basically the same size as the PCBs themselves) doubling my overall project size. 

For another project, I tried powering the project with that same 7.2V lithium polymer battery and it didn't startup the pic at all but started up the X-Bee connected to a 3.3V LP2981 on the same PCB.  And again, for some reason when I connect it to a 5.1V power supply (on the same Vin pin) it powers up fine. 

I have a 10uF over the Vin and a 0.1uF and 0.01uF on the Vout on both the 5V and 3.3V regulators (all across to ground).  The current is <100mA as required by the data sheet.  I even tried placing a large Cap at the Vin incase there was a large initial drain, but that didnt' work either.

 Anyone have any ideas?

Thanks!

Offline airman00

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Re: Voltage regulator problem
« Reply #1 on: October 13, 2008, 10:23:28 AM »
I'm using a LP2981 low drop out 5V voltage regulator along with a dsPIC30F3012 for a couple small (in size) applications and I seem to be having a powering  problem. 

For the first application I tried using 2 x 2032 button batteries (adding to ~6 volts).  For some reason this didn't work

What do you mean it didnt work ? Did you take a voltage reading or a current reading ?
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Offline Admin

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Re: Voltage regulator problem
« Reply #2 on: October 15, 2008, 05:25:05 AM »
Got an oscope? Hook it up and look for noise or voltage drops. I'm suspecting those button batteries have a large voltage drop as current is drained, causing your system to reset.

Got battery specs or datasheet link?

Also, try turning off brownout (I'm assuming your dsPIC has that option) so it doesn't reset with noise.


and a quick stupid check: are you sure they fully charged when you recharged your batteries?

Offline jsmokerTopic starter

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Re: Voltage regulator problem
« Reply #3 on: October 15, 2008, 08:48:35 AM »
Yeah, I was thinking of the voltage drop, but I tried putting a rediculous cap (15000uF) at the battery and it didn't help.

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Re: Voltage regulator problem
« Reply #4 on: October 15, 2008, 09:03:08 AM »
Well, a cap would smooth the noise out . . . but if the average voltage drops, a cap will only work for a fraction of time until the reset occurs.

Also, measure the current with a multimeter, too . . .

 


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