heating problem
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Greetings,
I have a BS2P-40 Stamp that is getting way too hot. The LM1121A
regulator chip is reading about 45C (113F). I have pin 40 going to a
+12 Vdc supply. I have all the outputs pulled up to the 5 volt line
through 10K resistors except for 4 inputs that are pulled down. I
have 2 optocouplers connected and did have 4 LEDS but disconnected
them.
Surely I'm not stressing the Stamp chip already? I'm only using 18 of
the 32 aux I/O and pulling 60 mA current from the 12v. Sure don't
want to burn up a $100 chip. Any ideas? Anyone know if this is
normal?
Paul Coy
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I have a BS2P-40 Stamp that is getting way too hot. The LM1121A
regulator chip is reading about 45C (113F). I have pin 40 going to a
+12 Vdc supply. I have all the outputs pulled up to the 5 volt line
through 10K resistors except for 4 inputs that are pulled down. I
have 2 optocouplers connected and did have 4 LEDS but disconnected
them.
Surely I'm not stressing the Stamp chip already? I'm only using 18 of
the 32 aux I/O and pulling 60 mA current from the 12v. Sure don't
want to burn up a $100 chip. Any ideas? Anyone know if this is
normal?
Paul Coy
__________________________________________________
Do you Yahoo!?
New DSL Internet Access from SBC & Yahoo!
http://sbc.yahoo.com
Comments
From: "PRCOY" <prcoy@
> Greetings,
>
> I have a BS2P-40 Stamp that is getting way too hot. The LM1121A
> regulator chip is reading about 45C (113F). - snip -
Keep in mind that is the case temp, junction temp is hotter!
> I have pin 40 going to a +12 Vdc supply.
The specs say 5.5 to 12Vdc into pin40, your running it at max.
> I have all the outputs pulled up to the 5 volt line through 10K resistors
If they are being driven low, that is 0.5ma each no biggie there
> except for 4 inputs that are pulled down. I
> have 2 optocouplers connected and did have 4 LEDS but disconnected
> them.
Are you using current limiting resistors for these?
> Surely I'm not stressing the Stamp chip already? I'm only using 18 of
> the 32 aux I/O and pulling 60 mA current from the 12v. Sure don't
Seems like I read where 60ma was the max current.
> want to burn up a $100 chip. Any ideas? Anyone know if this is
> normal?
>
> Paul Coy
Paul 7.5Vdc is the recommended supply voltage & current draw should be kept
below 60ma.
however the internal regulator has (I believe) thermal shutdown, and even if
you do fry it, you can always add a 78L05 to VDD.
But if you really want to play it safe, I use a 75 ohm 1/2 watt resistor
between 12Vdc and Vin and a 470uf 16v cap across Vin to Vss. This will take
the stress off the regulator, and provide extra filtering as well.
Lonnie - KF4HAZ -