RECTIFICATION

A rectifier diode passes current in only one direction under ideal operating conditions. This makes it useful for changing ac to dc.
Generally speaking, when the cathode is negative with respect to the anode, current flows; when the cathode is positive relative to the anode, current does not flow. The constraints on this behavior are the forward breakover and avalanche voltages. During a little less than half the cycle, the diode conducts, and during a little more than half the cycle, it does not conduct. This cuts off slightly more than 50 percent of every ac cycle. Depending on which way the diode is connected in the circuit, either the positive part or the negative part of the ac cycle is blocked.