Explain what each stage of a power supply does, compare rectifier types, and read the symbols in figure G7-1.
Syllabus: Power supplies; schematic symbols
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 13 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
A rectifier turns AC into pulses of DC. A half-wave rectifier blocks one half of the AC cycle, so it converts 180° and needs one diode. A full-wave rectifier flips the other half too, so it converts 360° and gives twice as many pulses, at twice the AC frequency. It needs two diodes on a center-tapped transformer, or four in a bridge.
RememberHalf-wave: 1 diode, 180°. Full-wave: 360°, pulses at twice the AC frequency. Two diodes + center tap = full-wave.
Rectifier output is lumpy DC. The filter smooths it: capacitors hold the voltage up between pulses, inductors resist changes in current. Diodes and transformers belong earlier in the chain.
RememberPower supply filter = capacitors and inductors.
Filter capacitors can stay charged for a long time after you unplug a supply. A bleeder resistor across the output discharges them when power is removed, so they are less of a shock hazard.
RememberBleeder resistor: discharges the filter capacitors when power is removed.
A switchmode supply chops the power at high frequency. A transformer or filter part for a higher frequency can be much smaller, so the supply is smaller and lighter than a linear one with a mains-frequency transformer.
RememberSwitchmode: high-frequency operation allows smaller components.
Match each symbol by its giveaway detail. A FET has a circle with a channel bar and a gate, a bipolar NPN has an emitter arrow pointing out, a Zener has a bar with bent ends, a solid core transformer has bars between two coils, and a tapped inductor is a single coil with a tap wire.
Memory hookNPN = Not Pointing iN: the emitter arrow points away from the base.