Diodes come in many shapes and sizes. High-current Diodes are often attached to a heat-sink device to reduce their operating temperature. It is possible to place Diodes in parallel to increase the current-carrying capacity, but the VI characteristics of both Diodes must be closely matched to 2cl2FL ensure that current divides consistently (although a small resistor can be slipped into series with each diode to help equalize the currents). All Diodes have some loss current (current that gets through when a diode is reverse-biased).
This loss current-better known as the reverse current (IR)-is tiny, typically within the nano ampere range. Diodes also have a maximum allowed reverse voltage, peak reverse voltage (PRV), or peak inverse voltage (PIV), above which a large current will flow in the wrong direction. If the PIV is surpass, the diode gets zapped and may become permanently damaged. The PIV for Diodes varies from a few volts to as much as several thousand volts. One method for achieving an effectively higher PIV is to place Diodes in series. Again, it is important that Diodes are matched to ensure that the reverse voltage divides equally (although a small resistor slipped into parallel with each diode can be used to equalize the reverse voltages).
Other things to consider about Diodes include maximum forward current (IF), capacitance (formed across the pn junction), and reverse recovery time. Most Diodes have a 1-prefix designation (e. gary., 1N4003). The two ends of a diode are usually named from each other by a mark. For glass-encapsulated Diodes, the cathode is designated with a black band, whereas black-plastic summarized Diodes use a white band. If no symbols are present (as seen with many power Diodes ), the cathode may be a bolt like piece. This piece is inserted by way of a heat-sink device (piece of metal with a hole) and is fixed down by a fanatic. A fiber or mica cleaner is used to segregate the cathode electrically from the metal heat sink, and a special plastic grease is put between the cleaner and heat sink to enhance winter conductivity.
A zener diode is a device that acts as a typical pn-junction diode when it comes to forward biasing, but it also has the ability to conduct in the reverse-biased direction when a specific breakdown voltage (VB) is reached. Zener Diodes typically have breakdown voltages in the array of a few volts to a few hundred volts (although larger effective breakdown voltages can be reached by placing zener Diodes in series).