what is the diffference between forward current and reverse current?
what is the diffference between forward current and reverse current?
Current flows through a forward-biased PN junction. Current is blocked in a reverse-biased PN junction, but only to the extent that the reverse bias voltage is less than the peak inverse voltage (PIV) rating of the diode.
A reverse biased diode always has a very small current flow due to to what are called minority carrier holes and electrons. They make their way through the space-charge (depletion) region because of the reverse voltage. As the reverse voltage is increased so does the electric field in the diode, and these minority carriers gain more energy, more speed, and actually collide with the lattice. When enough reverse voltage is applied the minority carriers start actually knocking off electrons when they collide with the atoms in the lattice. More electrons means more current and more collisions, and this creates an avalanche effect which breaks down the whole lattice and you get full conduction avalanche breakdown
There is a difference between avalanche breakdown and true zener breakdown. Avalanche breakdown is what is described, above. True zener breakdown only occurs in heavily doped junctions where the reverse voltage becomes stong enough to move electrons from their valance bands. The valance electrons move across the depletion region by what's called "tunneling" and there is no avalanche (multiplication) effect, because all the valence electrons are affected at the same time. This process only applies to zener diodes up to about 6 volts, although diodes are called 'zener' diodes whether they use avalanche breakdown or tunneling.
Current flows through a forward-biased PN junction. Current is blocked in a reverse-biased PN junction, but only to the extent that the reverse bias voltage is less than the peak inverse voltage (PIV) rating of the diode.
A reverse biased diode always has a very small current flow due to to what are called minority carrier holes and electrons. They make their way through the space-charge (depletion) region because of the reverse voltage. As the reverse voltage is increased so does the electric field in the diode, and these minority carriers gain more energy, more speed, and actually collide with the lattice. When enough reverse voltage is applied the minority carriers start actually knocking off electrons when they collide with the atoms in the lattice. More electrons means more current and more collisions, and this creates an avalanche effect which breaks down the whole lattice and you get full conduction avalanche breakdown
There is a difference between avalanche breakdown and true zener breakdown. Avalanche breakdown is what is described, above. True zener breakdown only occurs in heavily doped junctions where the reverse voltage becomes stong enough to move electrons from their valance bands. The valance electrons move across the depletion region by what's called "tunneling" and there is no avalanche (multiplication) effect, because all the valence electrons are affected at the same time. This process only applies to zener diodes up to about 6 volts, although diodes are called 'zener' diodes whether they use avalanche breakdown or tunneling.
