Special Purpose Diodes Week of 18th August 2008

Let us consolidate what you have learnt so far !! Example 4.6 of Malvino. Question by 200801133

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

General Purpose PCB

A sample Printed Circuit Board (PCB)

DC Connector Scale in cm/mm

Positive clipper RS 0.7 V Vin RL Vout

Negative clipper RS Vin RL Vout -0.7 V

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

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

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

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

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

Simulating the Zener Diode

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

A zener waveshaping circuit Power supply RL VZ + 0.7 V -VZ - 0.7 V

Power supply RZ Zener diode second approximation VZ

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.

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

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.

Optoelectronics Technology of optics and electronics LEDs Photodiodes Optocouplers Laser diodes

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.

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

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

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

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

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