Circuit Building Blocks

The goal here is to have a page of various transistor circuits, but for now I'll include op amps.

They should be simple enough that you could combine them in a larger design (i.e. as part of an op amp or ASIC). I'm not going to include fundamental circuits (such as: https://en.wikipedia.org/wiki/Template:Transistor_amplifiers or basic op amps which you can find in Electronics for Inventors or AoE.)

These are sometimes called Topologies. Like a map. A map topology. If maps lie, then it's likely these circuits will lie as well. Expect any examples to be missing required components to work.

Transistor Circuits

Programmable Unijunction Transistor Sawtooth

Make Electronics: Learning by Discovery, Charles Platt

Relaxation Oscillator

Amp Hour 579, A relaxation oscillator is filling up a capacitor, at which point when the cap reaches a certain voltage, the charge is dumped (possibly by a transistor) and the cycle repeats again. It may look like a sawtooth.

On the other hand, a triangle, would be a circuit that only charges/discharges the capacitor (in equal amounts)(ramp waveform: page 34 student manual for art of electronics).

Quick Bits Examples

Most of these are also referenced in the Art of Electronics.

• Differential Pair
• Current Mirror (Wilson ver.)
• Bandgap Voltage Reference - Limiting temperature effects in semiconductors.

Unity Gain

• 

  Similar diamond buffer made with op amp. Note the transistors are powered by the supply rails of the op amp.

• 

  Fairchild example of the diamond buffer.

• https://en.wikipedia.org/wiki/Diamond_buffer - Unity gain, high current.

https://www.eevblog.com/forum/projects/opamps-die-pictures/msg5450288/#msg5450288

Simplest Band Gap Reference

By Bob Widlar. Practical Electronics | August 2025 | page 74. It is simpler than the Brokaw reference, which has an op amp. This is another writeup similar to the quickbits one above. Don't forget that most disposable electronics use the TL431. There are also bandgap reference ICs available for 60¢ each. The LM404 series (covered by multiple vendors) comes up with 950+ results on Digikey.

• 

Op Amp Circuits

Howland Topology

• Current Source (Howland) Voltage Controlled Current Source, see also: https://www.eevblog.com/forum/beginners/current-source-with-p-channel-mosfet-not-working-as-expected/msg5447837

Transimpedance Amplifier

A way to convert current to voltage. It's just an op amp with a resistor in the feedback loop. Per amp hour 579, and talking of ADC design. There is a lot written about this, so one can dig in if necessary. e.g.

• https://www.ti.com/lit/ta/ssztbc4/ssztbc4.pdf - What You Need to Know about Transimpedance Amplifiers – Part 1

Misc Circuits

Debouncing

Diodesgonewild has a thorough (the best i've seen) video on the 555 timer. There are actually 2 videos. One of the circuits he shows is debouncing for an on-off switch.

Further Reading

• Practical Electronics, Fourth Edition, Paul Scherz, Simon Monk
• Art of Electronics, 3rd Edition, Horowitz, Hill
• Transistor Circuits, Rufus Page Turner

I have seen other books over the years. I need to make a note to add them here. As always, beware of books that use verbosity as a weapon.