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Need help with a transistor

Need help with a transistor

Need help with a transistor

(OP)
I want to switch a transistor (as below) that will supply current via the 100R resistor when power is applied.  However, I would like to be able to turn the transistor OFF and ON using a micro.  Any ideas?



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 |________|
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 |           | | 100R
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 |            |____________ rest of cct
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_|___________________ GND

RE: Need help with a transistor

Put another transistor (or FET) between the lower base bias resistor and ground.  Control the new transistor/FET with the micro.

RE: Need help with a transistor

(OP)


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 |           | | 100R
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    \|_______/\______ micro
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|_________________ gnd



I think this is what you mean.

The problem with this is that the micro will ultimately control the 100R load.  What I need is when power is applied, the PNP transistor is on, regardless of the micro.  Then I need to turn the PNP transistor OFF with a micro.

RE: Need help with a transistor

Using the schematic you just drew, add a pull-up resistor to the second transistor's base.  On start-up, the transistor will conduct and turn the whole shebang on.  To turn it off by way of the micro, pull the base to ground.

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