halvvågs

Halvvågs, or half-wave, is a term used in physics and electronics to describe either half of a wave cycle or a circuit that conducts during only one half of each cycle. In Swedish contexts it refers to half of a sinusoidal waveform, from one zero crossing to the next, and is used in analysis of alternating current signals. A common implementation is the halvvågsrectifier: a single diode connected to an AC source and a resistive load that conducts during one half-cycle while blocking during the other.

Mathematically, if the input is a sinusoid v(t) = Vp sin(ωt), the half-wave rectified output is v_out(t) = max(0, Vp sin(ωt)) for the orientation that passes positive half-cycles, or v_out(t) = min(0, Vp sin(ωt)) for the opposite orientation. The result is a pulsating DC waveform that contains a DC component plus ripple at the same frequency as the input.

Electrical characteristics include a DC output equal to Vp/π across an ideal resistive load, and an output ripple corresponding to the non-conducting half-cycles. The rectifier’s efficiency is limited; for an ideal half-wave rectifier feeding a purely resistive load, the maximum theoretical efficiency is about 40.5%. The ripple frequency equals the supply frequency, so smoothing with a capacitor or filter is often used to obtain steadier DC.

Applications are common in simple power supplies, envelope detectors, and introductory electronics experiments. Related concepts include full-wave rectification, diode operation, and rectifier circuits.