the half-wave rectifier
Mains and most signals are AC — they swing positive then negative, back and forth. But chips want DC, a steady one-way supply. A rectifier is the converter, and the half-wave rectifier is the simplest possible one: a single diode in series with the load. It is like a turnstile on a tide — it lets the incoming flow through but blocks the outflow.
Here is how it works on a sine wave. During the positive half of each cycle the diode is forward biased and passes the current to the load (minus its ~0.7 V drop). During the negative half the diode is reverse biased and blocks, so the output is simply zero. The result is a lumpy train of positive humps with gaps where the negative halves used to be — pulsing DC, not smooth, but at least always one polarity.
It is cheap (one diode) but wasteful: half the waveform is thrown away, the output sags to zero every cycle, and the ripple is large. It is fine for a trickle charger, a simple signal detector, or anywhere a rough average is enough. For real supplies we add a smoothing capacitor and usually upgrade to full-wave, which uses both halves.
Feed a 10 V peak sine into a diode and load. The output is a series of humps peaking at ~9.3 V (10 V minus the 0.7 V drop), each followed by a flat-zero gap lasting the whole negative half-cycle.
Half-wave: positive humps pass, negative halves are blocked to zero.
Beginners expect 'rectified' to mean 'DC and smooth'. Half-wave output is one-directional but still pulses all the way to zero every cycle — smoothing is a separate, later job done by a capacitor.