AVR-Chat

Wow Andy!  So... fiery!

The changes were made because we weren't sure what a PC power supply outputs at power-up when the load on the 5V is only in the tens-hundreds milli-amps.  Using a scope to determine that is irrelevant, because another PSU might do something else.  Still, I did check it.

You would be right about the headroom if I wasn't using an LP3966 "3A Fast Ultra Low Dropout Linear Regulators" that drops only 80mV at 300mA.
Plenty headroom :-)

What's wrong with a linear regulator after a switched mode regulator, please?  I'm really interested in that?

What makes you think I didn't test it with DVM/Scope?  I did, saw a curve, and couldn't tell if it's acceptable or not.
If you were doing it with a DVM/scope, how would you define what should work or not?


I'm no yank, but I don't get either "Belt & Braces" nor the "suspenders" expression... what's it supposed to mean?

Thanks,

Cat

> To: AVR-Chat@yahoogroups.com
> From: andrewdavid.mathison@freenet.de
> Date: Fri, 12 Mar 2010 18:59:43 +0100
> Subject: [AVR-Chat] Re: Code stuck waiting for SPI transmission but  only after power-up
> 
> Hi,
> 
> I have to agree witrh those talking about power problems, it sounds to me also like a typical "brown out" problem....
> 
> If it was happening to me, I would be using a 'scope and a good DVM - Together! To analyse the problem as best I could.....
> 
> If I understood you correctly, you made changes to the power in some manner (why as any normal PC supply delivers a good stable voltage!)
> 
> BUT, a PC power supply is generally a switched mode power supply and putting a linear regulator after it is HIGHLY NOT recommended!!!!
> 
> Also a linear regulator needs some "headroom", after a PC power supply THERE IS NO HEADROOM left here !!!! I think this is your problem!! 
> 
> The linear regulator is dropping anything up to 2.5 volts.......depending upon its type and the actual load of course.....
> 
> I am a great believer in "Belt & Braces (suspenders for you yanks!!)", but here its WRONG WRONG WRONG.....
> 
> And doing it without checking/using a DVM/Scope is also WRONG WRONG WRONG.....
> 
> I hope this helps you further.....
> 
> Greetings from
> 
> Andy Mathison
> 
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> 
> 
> 
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