Analog Electronic Circuits - 02 - Problems (Diodes).pptx

Analog Electronic Circuits - 02 - Problems (Diodes).pptx

1. Analog Electronic Circuits Dr. Adel Rawea

2. Diodes Problems 03

3. Examples EXAMPLE 1 : For the series diode configuration of next Figure Determine , , and .   Dr. Adel Rawea 3 Solution : Since the applied voltage establishes a current in the clockwise direction to match the arrow of the symbol and the diode is in the “on” state,

4. Examples EXAMPLE 2 : Repeat last Example with the diode reversed. Determine and   Dr. Adel Rawea 4 Solution : Removing the diode, we find that the direction of I is opposite to the arrow in the diode symbol and the diode equivalent is the open circuit no matter which model is employed.

5. Examples EXAMPLE 3 : For the series diode configuration of Figure 1 , Determine , , and .   Dr. Adel Rawea 5 Solution : the level of applied voltage is insufficient to turn the silicon diode “on.”. The point of operation on the characteristics is shown in Figure 2., establishing the open circuit equivalent as the appropriate approximation, as shown in Fig. 2.18 . The resulting voltage and current levels are therefore the following: Figure 1 Figure 3 Figure 2

6. Examples EXAMPLE 4 : for the series circuit of Figure 1 , Determine , and .   Dr. Adel Rawea 6 Solution : the resulting current has the same direction as the arrowheads of the symbols of both diodes, and the network of Figure 2. results because The resulting voltage is   Figure 1 Figure 2 and

7. Examples EXAMPLE 5 : for the parallel diode configuration of Figure 1 , Determine , , and .   Dr. Adel Rawea 7 Figure 1 Figure 2

8. Examples Dr. Adel Rawea 8 Solution : For the applied voltage the “pressure” of the source acts to establish a current through each diode in the same direction as shown in the last Figure 2. the applied voltage is greater than 0.7 V, both diodes are in the “on” state. The voltage across parallel elements is always the same and

9. Examples EXAMPLE 6 : for the network of next Figure 1 , Determine .   Dr. Adel Rawea 9 Solution : The voltage must be the same across parallel elements. There is a period of build-up of the supply voltage from 0 V to 12 V even though it may take milliseconds or microseconds. At the instant the increasing supply voltage reaches 0.7 V the silicon diode will turn “on” and maintain the level of 0.7 V since the characteristic is vertical at this voltage—the current of the silicon diode will simply rise to the defined level. The result is that the voltage across the green LED will never rise above 0.7 V and will remain in the equivalent open-circuit state as shown in Figure 2 Figure 1 Figure 2 The result is:

10. Examples EXAMPLE 7 : for the network of Figure 1 , Determine and .   Dr. Adel Rawea 10 Figure 1 Figure 2

11. Examples Dr. Adel Rawea 11 Solution : The applied voltage (pressure) is such as to turn both diodes on, as indicated by the resulting current directions in the network of last Figure 2 Note the use of the abbreviated notation for “on” diodes and that the solution is obtained through an application of techniques applied to dc series–parallel networks. We have