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I know how to power the load with the transistor when the base is "on".

schematic

simulate this circuit – Schematic created using CircuitLab

But I sometimes need the opposite, to power the load when the base is "off". How to do that with transistors?

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    \$\begingroup\$ You will fry your BJT without a base resistor. Think of the base-emitter junction as a diode. \$\endgroup\$
    – DKNguyen
    Jul 2, 2019 at 0:22
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    \$\begingroup\$ what do you mean by base is off? \$\endgroup\$
    – jsotola
    Jul 2, 2019 at 1:06
  • \$\begingroup\$ @jsotola i meant when there is no current going in base \$\endgroup\$
    – Mirakul
    Jul 2, 2019 at 17:53

1 Answer 1

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R2 acts as the base resistor for Q1 and feeds current to the base to keep it on unless you turn on Q2 to "short" Q1's base current.

schematic

simulate this circuit – Schematic created using CircuitLab

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