Voltage Substractor simple circuit

[DaveE]

And make it even more complex? No thank you! Simplicity is king.

The problem with this statement is that while the schematic may be simple, the basic BJT device is anything but simple. Look at the schematic of a simple op-amp, like LM741. The reason they have so many transistors is to compensate for non-linear and non-ideal effects. In practice, for analog circuits you will most often see transistors used in pairs to help compensate for the imperfections of the basic devices. Analog transistor circuits just aren't simple in the real world.

It's really great that you are exploring this because it is the best way to learn, at a fundamental level, about analog circuitry. However, in a real EE lab a simple op-amp is the same size, the same cost, and works better than a single discrete transistor. Discrete transistors, in practice, are use for high frequencies, high power, and the simplest digital/switching applications.

Also, as I think has already been said, in your original circuit, if one diode is on the other will be (mostly) off. It is a classic logic circuit, like voting. Not a voltage input adder at all. You can see this if you consider a diode model that acts as a perfect switch, either 100% on or 0% on.

 

[berkeman]

After a bit of thread cleanup, this thread is done. Thanks everybody for trying to help Helena with her growing understanding of electronics.