One Transistor Oscillator

Introduction

This article is about an oscillator made with just one transistor:

Figure 1: One Transistor Oscillator.

You can see the circuit working in those videos:

Step 1: Design the Circuit

I drawn the circuit in PSpice simulations software to reduce the design time:

Figure 2: Circuit Design.

It is hard to determine the number of resistor capacitor feedback filters that are needed for the circuit to oscillate. This depends on the transistor AC current gain and this gain can change with temperature and is different for each transistor that you select.

I continued adding the resistor capacitor feedback filters until the transistor started oscillating.

Step 2: Simulations

Simulations show that the circuit is producing a sinusoidal oscillation:

Figure 3: Simulations.

Step 3: Make the Circuit

I did not trust the simulations because real life components are could be different from PSpice simulation models.

I continued adding resistor capacitor low pass filters until the transistor started oscillating.

I used a 2N4427 transistor:

Figure 4: Circuit Construction.

You do not really need a heat sink for this circuit. However, I connected a heat sink because I had one in stock.

Conclusion

It is also possible to make a square wave and triangle wave oscillator with Uni-junction Transistors (UJTs).