Complete Electronics Self-Teaching Guide with Projects

Diode Breakdown

22 Earlier, you read that if the circuit in Project 2.1 was not working correctly, then the diode may be in backward. If you place the diode in the circuit backward—as shown on the right in Figure 2.23—then almost no current flows. In fact, the current flow is so small, it can be said that no current flows. The V-I curve for a reversed diode looks like the one shown on the left in Figure 2.23.

Figure 2.23

The V-I curve for a perfect diode would show zero current for all voltage values. But for a real diode, a voltage is reached where the diode “breaks down” and the diode allows a large current to flow. The V-I curve for the diode breakdown would then look like the one in Figure 2.24.

Figure 2.24

If this condition continues, the diode will burn out. You can avoid burning out the diode, even though it is at the breakdown voltage, by limiting the current with a resistor.

Question

The diode in the circuit shown in Figure 2.25 is known to break down at 100 volts, and it can safely pass 1 ampere without overheating. Find the resistance in this circuit that would limit the current to 1 ampere. _____

Figure 2.25

Answer

Because 1 ampere of current is flowing, ...