The Seemingly Impossible Oscillator

Hackaday examines a circuit that looks like it shouldn't work, yet never fails to oscillate: the reverse avalanche oscillator. Built from just four components—a transistor, a capacitor, an LED, and a resistor—the transistor is wired backward with no base connection. The secret is avalanche breakdown: as the capacitor charges, voltage rises until it triggers a sudden cascade of electrons across the transistor's junction, causing an abrupt discharge. When the voltage drops, this avalanche stops and the cycle repeats, producing a steady LED flash. The result is a relaxation oscillator that defies every intuitive rule of circuit design.

Listen to this story

Hear this and more stories in a personalized audio briefing.

Open The Chonkerton