Silicon rectifier

Silicon rectifier diodes, are used in many applications from high voltage, high current power supplies, where they rectify the incoming mains (line) voltage and must pass all of the current required by whatever circuit they are supplying; this may be several tens of Amperes or more.

Carrying such currents requires a large junction area so that the forward resistance of the diode is kept as low as possible. Even so the diode is likely to get quite warm. The black resin case helps dissipate the heat.

The resistance to current in the reverse direction (when the diode is "off") must be high, and the insulation offered by the depletion layer between the P and N layers extremely good to avoid the possibility of "reverse breakdown", where the insulation of the diode fails due to the high reverse voltage across the junction.

Silicon diodes are made in many different forms with widely differing parameters. They vary in current carrying ability from milli-amps to tens of amps, some will have reverse breakdown voltages of thousands of volts; others use their junction capacitance to act as tuning devices in radio and TV tuners. Look in suppliers lists to see the many types available.