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I am trying to use a bipolar junction transistor to sink the current on an output pin:

schematic

simulate this circuit – Schematic created using CircuitLab

But when the base of Q1 is connected to 0V, and the base of Q2 is connected to 5V, there seems to be a large amount of current going through Q2 (1.28 amps). The only possible path that the current could take is from the base of Q2 to the emitter of Q2.

UPDATE: I meant to say "The only possible path that the current could take is from the base of Q2 to the collector of Q2."

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    \$\begingroup\$ Where is ground? and where is Q2 - I only see Q1 and Q5. Please check that the schematic you show represents the circuit you have. \$\endgroup\$ – Peter Bennett Jul 13 '14 at 0:57
  • \$\begingroup\$ You need resistors in the base leads of the transistors to limit base current, and thus collector/emitter current. Also, an NPN emitter follower can only pull things up - it can't pull things down. \$\endgroup\$ – Peter Bennett Jul 13 '14 at 1:35
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You need resistors in the base leads of the transistors to limit base current, and thus collector/emitter current. Also, an NPN emitter follower can only pull things up - it can't pull things down. – Peter Bennett

Thanks!

I fixed the problem by adding a 10K resistor to the base. I also rearranged the transistors so that Q2 is able to pull the output down; the collector of Q2 is connected to the output, and the emitter of Q2 is connected to GND.

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