Power supplies convert electrical energy from one form to another to run electronic devices. From early battery-powered systems to modern high-efficiency switchers, they have evolved dramatically. In the MicroBasement, power supplies connect vintage tube gear to today's electronics, showing how safety, efficiency, and size have improved over time. This write-up covers early battery supplies (A, B, C batteries), dangerous direct AC methods, transformers, vacuum tube and selenium rectifiers, linear supplies with filters and regulators, the shift to switching topologies (buck, boost, etc.), efficiencies, and key milestones.
Early radios and electronics used batteries exclusively because household AC power was not yet widespread. These batteries were consumables—mostly non-rechargeable dry cells that had to be replaced frequently, often every few weeks or months depending on usage. Prices in the 1920s–1930s were significant for the average household:
Batteries were heavy, expensive over time, and limited runtime. No AC power meant no hum, but the constant replacement cost was a major drawback.
When AC power became common, some early "AC-DC" sets connected filaments directly to the line voltage without an isolation transformer. This created "hot chassis" designs—one side of the 120V power line was connected directly to the metal chassis. Touching the set while grounded could deliver a lethal shock. Many people were electrocuted this way. Transformers eventually provided galvanic isolation, stepping voltage up or down safely, but they were heavy, bulky, expensive, and generated heat and hum.
In the early computer hobbyist days of the 1970s, a common project was converting portable TVs into video monitors for homebrew computers (NTSC in the US). These TVs often used "hot chassis" designs where one side of the AC line was directly connected to the chassis for cost savings. Hobbyists would connect video signals to the TV's input, but without proper isolation, the entire chassis could be live at line voltage. Touching the metal case or exposed connections while grounded could cause severe or fatal shocks. To make these conversions safe, hobbyists used isolation transformers (1:1, 120V to 120V) to float the TV's power supply relative to earth ground. This became a standard safety practice in the homebrew community when working with AC-DC TVs.
AC had to be converted to DC:
Linear supplies use a transformer, rectifier, filter capacitors, and regulator. Basic design math includes:
Early regulators used gas tubes (e.g., VR150); later zener diodes, then single-package ICs like the 78xx series. Linear supplies are simple, low-noise, and easy to repair (often just bad capacitors causing ripple), but inefficient (30–60%) and heavy due to large transformers and heatsinks.
Switching supplies dominate today (80–95% efficiency, small/lightweight). Common topologies:
They switch at high frequency (20 kHz–several MHz) using small inductors and feedback loops. Trade-offs include EMI noise and complexity, but far superior efficiency and size.
Power supplies evolved from dangerous direct AC and heavy batteries to efficient, safe switchers. Linear supplies powered vintage gear reliably; switching supplies enable modern portability. In the MicroBasement, they bridge tube radios (A/B batteries, transformers) to today's devices, showing how safety and efficiency drive progress.