Capacitive Transformerless Power Supply Calculator

Use the capacitive transformerless power supply calculator to find your circuit's output voltage and input current.

Current through the capacitor33.9606 mAleading the voltage by 90°

Capacitive reactance6.7726 kΩ1 ÷ (2π × 50 Hz × 470 nF) — FALLS with frequency, so a capacitor blocks DC and passes high frequencies

Reactance stores rather than dissipatesno real powera pure reactance takes energy in for a quarter cycle and gives it all back the next — which is why it limits current without producing heat

At 60 HzX_C 5.6438 kΩ

At 1 kHzX_C 338.6275 Ω

At 1 MHzX_C 338.6275 mΩ

The formula

X_L = 2πfL; X_C = 1 ÷ 2πfC

Opposite slopes

Inductive reactance rises with frequency and capacitive reactance falls. That single asymmetry is the basis of every passive filter: put a capacitor across a signal and it shunts high frequencies to ground; put an inductor in series and it blocks them.

At DC the two are at their extremes. A capacitor's reactance is infinite, so it blocks DC entirely — which is exactly what a coupling capacitor is for. An inductor's is zero, so it is a plain wire, which is why a transformer does nothing on DC and why a motor winding draws destructive current if fed DC.

Reactance limits current without dissipating power. It absorbs energy for a quarter of a cycle and returns all of it the next, so unlike a resistor it does not get hot. That is the principle behind a capacitive dropper and behind reactive ballasts — and also why reactive current still heats the cable, which has real resistance even though the load does not dissipate.