Cursed circuits #5: capacitance multiplier
The article describes a circuit design known as a capacitance multiplier, which uses transistors and resistors to emulate a large capacitor without requiring a physically large capacitor component, essentially trading off spending on other components to save on capacitors.
Background
- The author, Michał "lcamtuf" Zalewski, is a well-known security researcher and engineer who writes about low-level electronics, computer architecture, and reverse engineering.
- A capacitance multiplier is a circuit that uses a transistor and a few passive components to make a small capacitor behave as if it were much larger — useful for smoothing power supplies or filtering noise without using bulky, expensive electrolytic capacitors.
- The joke about "saving money on capacitors by spending more on other components" plays on the irony: the technique replaces a cheap, large capacitor with a more complex circuit involving an op-amp or transistor plus a small capacitor — often costing more overall, but offering better performance or smaller size in certain niche applications.
- This article is part of a "Cursed Circuits" series, which explores odd, counterintuitive, or "bad practice" circuit designs that nonetheless teach something useful about electronics.