AVR-Chat

On Feb 13, 2005, at 1:16 PM, Valerij Avrealij wrote:

> Hello.
>
>  Some words about 7805,ISP and my AVR.
>  First of all my programmer works fine with mega8 and 7805,

Thats nice but we still don't know much about "your" circuit. The 
reason you are having problems is that something is different. Is this 
board of your design? Is everything identical, same hardware, but for 
the exchange of Atmega8 and tiny15/90s2343?

>  but when I
>  connect my ISP to tiny15 or 90s2343 also powered from 7805 or from
>  another source (for example, power supply (AC 220V -> DC 5V)) the 
>  current is very high.

Once again is it the exact same board or just same regulator P/N? If 
two 5 volt regulators are connected in parallel (the one on your board 
and the one in your ISP) then its very unlikely they both agree on the 
same value of "5.0 volts". With luck one will simply source while the 
other sinks (both get hot). Without luck the two will oscillate (both 
get hot).

>  Also very interest situation is that, when I connected swiched ON ISP
>  to the board all are OK, but if I connected ISP with breaked VCC to
>  the board (but board VCC is not breaked (it is swiched ON)), and than
>  turn on the ISP I have very high current.

I don't understand the term "breaked VCC" in the above context. Am lost 
as to the difference between "breaked" and "switched." Am guessing you 
powered the circuit, then powered the ISP, and found high current. Also 
guessing that previously you did NOT power your circuit but the 
circuit's 7805 got hot when the ISP was powered, which is what lead to 
my previous suggestion to put a diode immediately after the 7805 
regulator before 5 volts reaches either the AVR or ISP header.

If the 7805 does not get hot with the board power off and the ISP power 
on, and the device programs, then that is the way things are supposed 
to work. Is what you were supposed to be doing in the first place. But 
if in this case the unpowered regulator gets hot you need to disconnect 
it, or use a diode rectifier in the circuit to automatically disconnect 
it, or select a different model 3-terminal 5 volt regulator.

>  Sorry for tangled note.

Would help a bunch if you didn't send HTML formatted email. I had to 
reformat your text to form a proper reply.

--
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.