Using a transistor to add to max current output from a opamp?
If your goal is simply to increase the current sourcing capability of an op-amp, the canonical way to do it is:







simulate this circuit &ndash; Schematic created using CircuitLab

A transistor used in this configuration is known as an emitter follower. The configuration is also known as "common collector", since the collector is shared between the input and the output of the transistor.

Your feedback elements go in the dotted box according to what you want the op-amp to do, just as if you hadn't added the transistors.

By incorporating Q1 in the feedback loop, the op-amp's gain will make significantly reduce any non-linearities in the transistor. Further, if you already have an op-amp circuit that does what you want, except you need it to source more current, adding the transistor this way won't significantly alter the function of your circuit.

If you also need to sink current:







simulate this circuit

This configuration, where one transistor sources and the other sinks current, is known as push-pull.