Solved Problem on Diode

diode solved Problem  N° 1

Calculate the value of current For the circuit shown in Figure.

Solution :

The diode is forward biased because the applied voltage is connected so that its positive terminal is applied to the anode and the negative terminal is applied to the cathode. Because a silicon diode is being used, the forward voltage drop will be 0.7 V. With an applied voltage of 8.5 V and a circuit resistance of 1.2 kΩ, the circuit current will equal.

The lower left quadrant of the four sections in Figure 2 shows what reverse current will pass through the diode when a reverse bias voltage is applied. As you can see from the inset, a diode is reverse biased by applying a negative potential to its anode and a positive potential to its cathode. In this instance, current is effectively reduced to zero and the diode is said to be OFF and equivalent to an open switch.

Figure 2 : junction diode voltage-Current characteristic curve

These characteristics can be seen in the reverse curve in Figure 2 Beginning at the graph origin and following the curve into the reverse quadrant, you can see that the reverse current through the diode increases only slightly (approximately 100 uA). Throughout this part of the curve the diode is said to be blocking current because the leakage current is generally so small it is ignored for most practical applications. If the reverse voltage (VR) is further increased, a point will be reached where the diode will break down, resulting in a sudden increase in current. The point on the reverse voltage scale at which the diode breaks down and there is a sudden increase in reverse current is called the breakdown voltage. Referring to the reverse curve in Figure 2, you can see that most silicon diodes break down as the reverse bias voltage approaches 50 V. For example, the IN4001 low-power silicon diode has a reverse breakdown voltage (which is sometimes referred to as the Peak Inverse Voltage or PIV) of 50 V listed on its manufacturer’s data sheet. If this reverse bias voltage is exceeded, an avalanche of continuously rising current will eventually generate more heat than can be dissipated, resulting in the destruction of the diode.
 Semiconductor materials, and therefore diodes, have a negative temperature coefficient of resistance. This means as temperature increases (T↑), their resistance decreases (R↓).

self test Problem Diode

Use the following questions to test your understanding of Junction diode

1. What is the typical forward drop across a silicon diode?
2. What value of barrier voltage has to be overcome in order to forward bias a silicon diode?
3. How many P-N junctions are within a junction diode?