What portion of the AC cycle is converted to DC by a half-wave rectifier?

A complete alternating current (AC) cycle spans exactly 360 degrees, consisting of a positive half and a negative half. A half-wave rectifier uses a single diode to allow current to flow only during one of these halves. Because it only passes either the positive or the negative half of the waveform while blocking the other, it converts exactly 180 degrees (one half of the full cycle) into usable pulsating direct current (DC). The remaining 180 degrees of the AC cycle are simply ignored.