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Regulator bad?

 
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 04 March 2006, 0:43 AM    Post subject: Regulator bad? Reply with quote
the voltage with no external connection on pin 21 (Vcc) is about 3V rather than 5V. There are no other connections to the chip carrier. The The processor runs OK, blinks the LEDs.

Do I have a bad regulator?

clue:
I disconnected the Vin power and fed 5V to pin 21.
Then I reconnected my DS1307 for which I was developing code.
Works fine but it didn't with Vcc at 3V.
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 04 March 2006, 1:38 AM    Post subject: Reply with quote
You might check the input voltage (pin 24). If the voltage is too low, the output will be low as well.

The regulator used has a relatively large drop-out voltage. You need to feed it at least 7 volts (actually, the specifications say 6.7) in order to get a 5 volt output.

As a side note, I have run a ZX-24 for several days with 3 volts supplied to pin 21. This voltage does not meet the Atmel specification for running the processor at 14.7MHz but this particular device seemed to function correctly. The other devices on the ZX-24 are in spec down to 3 volts.
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 04 March 2006, 1:43 AM    Post subject: Reply with quote
Yes, I checked the input voltage as the first thing. It's 10.4VDC.

The Mega32 works at 3V but DS1307 doesn't work at 3V. Or at least the I2C command for ZBasic doesn't work correctly - it hangs the processor - the background task toggling an LED stops running - no blinking. I have 2.7K pull-ups on the I2C lines.

so do you think I have a bad regulator?
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 04 March 2006, 2:53 AM    Post subject: Reply with quote
Quote:
so do you think I have a bad regulator?

If the output is only 3 volts with 10 volts input and nothing connected to pin 21, the regulator is not doing its job.

I mention testing while having nothing connected to pin 21 because trying to draw too much current from the regulator will also cause the output to be low. The regulator is only able to supply 30-40mA to external circuitry. This amount includes the aggregate current sourced to external devices through the I/O pins. It is best to test the regulator with nothing connected to any of the pins except 1-4, 23 and 24.
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 04 March 2006, 3:36 AM    Post subject: Reply with quote
yes, the voltage is low without any external devices connected.
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 04 March 2006, 5:16 AM    Post subject: Reply with quote
Sounds like it's bad; we'll replace it. Unless you say otherwise, I'll have it sent to the same address as before. You can keep the one you have until the new one arrives.
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 04 March 2006, 6:40 AM    Post subject: Reply with quote
Thank you - this is more than I expected by far!

(I'll return the faulty one)
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 07 March 2006, 3:45 AM    Post subject: Reply with quote
replacement received very quickly! THANKS!
working fine. Failed one is en route back.
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spamiam



Joined: 13 Nov 2005
Posts: 665
Posted: 07 March 2006, 20:41 PM    Post subject: Reply with quote
Any idea about why the regulator failed?

So far I have never burned one out, but usually I supply my own 5v regulated power.

I am always a little worried about overloading the on-board reg. However, it is usually quite enough for all the I/O and LED driving someone is likely to do. So it is a little hard to fry it. I always worry about reverse polarity and similar goof ups.

-Tony
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 08 March 2006, 3:18 AM    Post subject: Reply with quote
as to why the regulator semi-failed (it put out 3.4V instead of 5V) - I didn't put a load on it. So it must be just one of those infantile failures.
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