Transformer action
A transformer transfers AC energy between windings by mutual induction. The primary winding receives energy. The secondary winding supplies the load. A transformer does not normally work from steady DC because a changing magnetic flux is required.
Turns ratio
For an ideal transformer, voltage ratio equals turns ratio. Current ratio is inverse to the turns ratio.
Vs/Vp = Ns/Np
Step-up and step-down transformers
A step-up transformer has more turns on the secondary than the primary. A step-down transformer has fewer secondary turns. Isolation transformers provide electrical separation between circuits.
Transformer losses
Copper loss occurs in the winding resistance. Core losses include hysteresis and eddy-current losses. Leakage flux and winding resistance also reduce performance. Laminated cores reduce eddy-current loss in low-frequency transformers.
Transformer as a matching device
A transformer can match one impedance to another. The impedance ratio is the square of the turns ratio for an ideal transformer. This is useful in audio and RF circuits.
Rectification
A rectifier changes AC into unidirectional, pulsating DC. A half-wave rectifier uses one half-cycle. A full-wave rectifier uses both half-cycles. A bridge rectifier uses four diodes and does not need a centre-tapped secondary.
Smoothing
Rectifier output contains ripple. A capacitor across the load charges near the waveform peak and discharges between peaks. This reduces ripple. Inductor-capacitor filters can provide further smoothing.
Voltage regulation and stabilisation
A regulator keeps the output voltage within limits as input or load changes. Zener diodes and regulator ICs are common methods. A stabilised supply is important because supply changes can shift oscillator frequency or alter transmitter output.
Power-pack blocks
A basic linear supply contains a transformer, rectifier, smoothing filter and regulator. Some radio equipment uses switch-mode supplies. Each type has benefits and design limits.