Re: When I remove GND from AVR µP TINY15, become very hot.

Hi!

First, Thanks for all your help.

Second, I will try to include some schematics in here, I have not the the
picture in my head but will try to make it tomorrow.

The LED is an IR-LED, and I thought that if I calculate the hfe-value on the
Transistor (round 300) and if the PIN from TINY can give ~4.8 volt the
current over 2k2 resistor will be 2.2mA. Times 300 = 65 mA. That should the
LED handle (rated 100mA constant and 1 A pulse)

The strange thing happend when i removed the ground in a lab plate. I have
also (befor the lab test with ground) a pcb with the same schematics and
there could it not be the ground that is removed...?
Anyway, I discoverd the symphtoms first at the pcb. The LED "hang" and the
TINY gets hot. Then I conected it to a labplate (labdeck?!?) and dicovered
that if I pull the GND the current arised.

However on the pcb, if LED output gets a puls (+5v) it behave in the same
way as if I remove the GND.

I will privide a schematics to clear things.

Thanks
/Mats

"Pooh Bear" <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote in message
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Mats Myhrman wrote:

Hi!

My problem is that when I remove the GND from the µP (Tiny15) my LED
that is
connected via a BC327-40 goes on, the current seems to go through the
AVR.

The LED's anode is connected to +5V, the cathode is connected to the
Collector, base via 2k2 res to TINY output, and emmiter to GND.

The strange thin is that if I remove the GND connector to TINY, the µP
become soon very hot and the current is about 0.4 A. How can this work?
How
is the port inter connected inside the TINY, Anyone that has a good
link? Or
idea.

The uP is finding a route to ground eleswhere, presumably via a port pin
(
likely turning on an internal parasitic diode from the IC structure ) and
that's
upsetting it ! Hard to say more without a schematic.

Graham



.

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