FORWARD BREAKOVER

It takes a certain minimum voltage for conduction to occur when a p-n junction is connected in the manner shown by Fig. 1a. This minimum

Fig. 1. (a) Forward bias of a diode results in a flow of current. (b) Reverse bias normally produces near-zero current.

voltage is called the forward breakover voltage (or simply the forward breakover) for the diode. Depending on the type of material from which a diode is manufactured, the forward breakover voltage can range from about 0.3 V to about 1 V. If the voltage across the p-n junction is not at least as great as the forward breakover, the diode will not conduct appreciably. Forward breakover voltages of multiple diodes add together as if the diodes were batteries. When two or more diodes are connected in series with their p-n junctions all oriented the same way, the forward breakover voltage of the combination is equal to the sum of the forward breakover voltages of each diode. When two or more diodes are connected in parallel with their p-n junctions all oriented the same way, the forward breakover voltage of the combination is the same as that of the diode whose forward breakover voltage is the smallest. The p-n junction is unique in this respect. It doesn’t conduct perfectly in the forward direction, but it doesn’t act quite like a dc resistor when it is conducting.