1. Chapter 2: Diode Applications Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

2. Slide 1 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Load Line The Load Line plots all possible current (I D ) conditions for all voltages applied to the diode (V D ) in a given circuit. E/R is the maximum I D and E is the maximum V D . Where the Load Line and the Characteristic Curve intersect is the Q point , which specifies a particular I D and V D for a given circuit.

3. Slide 2 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Diode Approximations In Forward Bias: Silicon Diode: V D = .7V Germanium Diode: V D = .3V In Reverse Bias: Both diodes act like opens V D = source voltage and I D =0A

10. Slide 9 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Full Wave Rectification The rectification process can be improved by using more diodes in a Full Wave Rectifier circuit. Full Wave rectification produces a greater DC output.

12. Slide 11 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Bridge Rectifier Circuit Four diodes are required. V DC = 0.636 Vm [Formula 2.10]

13. Slide 12 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Operation of the Bridge Rectifier Circuit For the positive half of the AC cycle: For the negative half of the AC cycle:

14. Slide 13 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Center–Tapped Transformer Rectifier Circuit Two diodes and a center-tapped transformer are required. V DC = 0.636(V m ) Note that V m here is the transformer secondary voltage to the tap.

15. Slide 14 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Operation of the Center–Tapped Transformer Rectifier Circuit For the positive half of the AC cycle: For the negative half of the AC cycle:

16. Slide 15 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Note: V m = peak of the AC voltage. Be careful, in the center tapped transformer rectifier circuit the peak AC voltage is the transformer secondary voltage to the tap. Rectifier Circuit Summary

17. Slide 16 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Diodes “clip” a portion of the AC wave. The diode “clips” any voltage that does not put it in forward bias. That would be a reverse biasing polarity and a voltage less than .7V for a silicon diode. Clipper Diode Circuit

18. Slide 17 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. By adding a DC source to the circuit, the voltage required to forward bias the diode can be changed. Variations of the Clipper Circuit

19. Slide 18 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. By taking the output across the diode, the output is now the voltage when the diode is not conducting. A DC source can also be added to change the diode’s required forward bias voltage. Changing Output Perspective

20. Slide 19 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Clipper Circuits Summary

21. Slide 19 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Clipper Circuits Summary

22. Slide 20 A diode in conjunction with a capacitor can be used to “clamp” an AC signal to a specific DC level. Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Clamper Diode Circuits

23. Slide 20 A diode in conjunction with a capacitor can be used to “clamp” an AC signal to a specific DC level. Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Clamper Diode Circuits

24. Slide 21 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The input signal can be any type of waveform: sine, square, triangle wave, etc. You can adjust the DC camping level with a DC source. Variations of Clamper Circuits

25. Slide 22 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Summary of Clamper Circuits

26. Slide 23 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The Zener is a diode operated in reverse bias at the Zener Voltage (V z ). Zener Diode

28. Slide 24 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Zener Calculations

32. Slide 28 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Operation of a Voltage Doubler Circuit The 1 st capacitor charges up to V m during the positive half of the cycle, then the 2 nd capacitor charges up to V m in the same polarity as the 1 st capacitor, finally the output is the sum of the voltages across both capacitors: Vout = 2V m

33. Slide 29 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Voltage Tripler and Quadrupler Circuits By adding more diode-capacitor networks the voltage can be increased.