At 07:58 AM 10/18/99 +1000, you wrote:
>> Add an additional 1.5k resistor from base to ground,to prevent self
>> turn-on.
>
>  That may apply to the FET, but where would you find enough leakage
>current in your circuit, over the PCB or in the PIC to turn on a
>darlington?  Of course once the PIC is initialised, it provides this
>function as the output pulls down (when you tell it to!).
>

No, not enough PCB leakage, BUT if the darlington gets hot, couldn't the
input BJT turn itself on  due to CB junction leakage, unless we have such a
resistor at the input? Yes, if the PIC is indeed driving the base low, this
isn't an issue. BUT if the PIC were to tristate the pin,it would be another
story. I just thought it was cheap protection.

Sean


|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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