1. Special Purpose Diodes
Week of 18th August 2008

2. Let us consolidate what you have learnt so far !!
Example 4.6 of Malvino. Question by

3. PCB design process Computer Aided Design tools – OrCad
Schematic entry ( Design Check) Open or Short Circuits
Routing of design ( Design Check)
PCB creation example PCB Prototyping.pdf

4. General Purpose PCB

5. A sample Printed Circuit Board (PCB)

6. DC Connector
Scale in cm/mm

7. Positive clipper RS
0.7 V
Vin RL
Vout

8. Negative clipper RS
Vin RL
Vout
-0.7 V

9. Zener diode - Chapter 5 ( Book by Malvino )
Optimized for operation in the breakdown region
Main use: voltage regulation

10. Graph of zener current versus voltage
-VZ (Volts) 6 4 2 20 40 60
-IZ (mA) VZ 80
100
120
140
Graph of zener current versus voltage

11. Power supply A zener diode voltage regulator RS VS VZ RL
This circuit will regulate when the Thevenin voltage
facing the zener diode is greater than the zener voltage. RL
VTH = VS
RS + RL

12. Power supply RS VS VZ RL Assuming the zener is conducting: VS - VZ VZ
IL =
IZ = IS - IL RS RL

13. Reading datasheet of zener diodes
Data sheet of diode zener_datasheet.pdf

14. Simulating the Zener Diode

15. Zener waveshaping Back-to-back zeners:
One zener conducts as one breaks down
Clipping results

16. A zener waveshaping circuit
Power
supply RL
VZ V
-VZ V

17. Power
supply RZ
Zener diode
second approximation VZ

18. Zener diode ratings Maximum power = PZ(max) = VZIZ(max)
Available tolerances: 1, 2.5 and 20 percent
Zener resistance, RZT, increases at the knee of the characteristic curve
A derating factor such as 6.67 mW per degree for temperatures above 50 degrees Celsius is typical.

19. Load lines
The intersection of the load line and the zener diode is the Q (operating) point
When the source voltage changes, a different load line appears with a different Q point

20. What happens to VZ when VS varies from 20 to 30 volts?
1 kW V
-30
-20
-10 RS Q1 VS
-10 I
(mA) Q2
-20
VS = 20 V
30 V
-30
What happens to VZ when VS varies from 20 to 30 volts?
Load lines provide a graphical solution.

21. Optoelectronics Technology of optics and electronics LEDs Photodiodes
Optocouplers
Laser diodes

22. Power supply RS VS Light-emitting diode VS - VD IS = RS
The typical voltage drop for most LEDs is from 1.5 to 2.5 V.

23. Photodiodes are reverse biased and conduct when struck by light
Power
supply VS
Photodiode
Photodiodes are reverse biased and
conduct when struck by light

24. Optocoupler combines an LED and a photodiode
Signal
source
Power
supply V1 V2
Optocoupler combines an LED and a photodiode

25. Varactor diode Exhibits variable capacitance
Can tune resonant circuits
Applications include radio and television tuning

26. Less reverse bias
(more capacitance)
More reverse bias
(less capacitance)
Varactor symbol

27. A varistor diode can be used to protect
line-operated equipment from voltage surges.
A varistor diode is also called a transient suppressor