Associate CET · Competency 10.x — Power Supplies

🔋 Power Supply Calculator

The numbers behind a linear DC supply: transformer turns ratio, rectifier output voltage, filter-capacitor sizing for a target ripple, percent regulation, and efficiency. Pairs with the Rectifier Lab visualizer in the Circuits Lab.

Transformer Turns Ratio

The turns ratio sets how the transformer steps voltage up or down. Current steps the opposite way.

N_p / N_s = V_p / V_s = I_s / I_p
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Rectifier Output Voltage

From the transformer's secondary RMS voltage, this finds the peak and the resulting DC. Choose the rectifier type; diode drops are included (0.7 V silicon).

V_peak = V_rms × 1.414  ·  half: V_dc≈0.318·V_pk   full/bridge: V_dc≈0.637·V_pk
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Filtered vs. average: the 0.318/0.637 figures are the unfiltered average DC. Add a filter capacitor (next tab) and the output rises toward the peak voltage, with some ripple riding on top.

Filter Capacitor Sizing

A reservoir capacitor smooths rectified DC. Bigger cap and higher ripple frequency mean less ripple. Full-wave/bridge ripple is at twice the line frequency.

C = I_load / (f_ripple × V_ripple(pp))
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Ripple From a Given Capacitor

The reverse: if you already have a capacitor value, how much ripple will you get at a given load?

V_ripple(pp) = I_load / (f_ripple × C)
µF
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Percent Voltage Regulation

How much the output sags from no-load to full-load. Lower is better — a stiff (well-regulated) supply has a low percentage.

% Reg = ((V_noload − V_fullload) / V_fullload) × 100
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Power Supply Efficiency

The fraction of input power delivered to the load. Linear supplies are typically 40–60%; switching supplies 80–95%.

η = (P_out / P_in) × 100  ·  P = V × I
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A
W
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