Power Supply Block Diagram
1. Transformer: steps AC down (e.g., 120V → 12V AC) for safety/isolation. 2. Rectifier: diodes convert AC to pulsating DC (full bridge: 4 diodes, uses both half-cycles, efficiency ∼81%). 3. Filter: capacitor smooths the pulsating DC (larger C = less ripple, but higher inrush current). 4. Regulator: provides constant output despite input/load changes. Linear (7805, LM317) — simple, low noise, inefficient (η ≈ Vout/Vin). Switching (buck/boost) — complex, efficient (η > 85%).
Linear Regulators
The 7805 is the most famous: input 7-35V, output 5V ±5%, 1A max, internal thermal shutdown. Dropout voltage ≈2V (input must be >7V for 5V out). Excess voltage × current = heat. At 12V in, 5V out, 1A: P_dissipated = (12-5)×1 = 7W — needs heatsink! LDO (Low Dropout): dropout <0.5V. Better for battery applications (e.g., 3.7V Li-Ion → 3.3V).