Are there any caveats with tapping off the base of a BJT to drive a high-impedance load, such as a logic gate or op-amp? In the schematic below, I have an open-collector output from
U1 sinking base current from transistor
Q1 to operate a load. I would like to connect some downstream logic to the output of
U1 for use elsewhere in the circuit.
The only issue I can see with this approach is ensuring that the saturation voltage of the open-collector output is low enough to register "logic low" with the downstream logic. As long as the base current of
Q1 is relatively low, and
U1 isn't sinking much current, I think this is attainable. (The actual thresholds will depend on the components used, of course.)
Is this practice okay, or would I be better off buffering the output to
Q1 so all of the loads on
U1 are high impedance? Or, is there some other design practice that's more appropriate here?