1. 1 © Unitec New Zealand DE4401 F IELD E FFECT T RANSISTOR

2. Intro 2 © Unitec New Zealand

3. The JFET JFET has no PN junctions, has a narrow CHANNEL of N or P silicon between Drain and Source, surrounded by a gate of the opposite type, which creates an Electric Field to ‘pinch off’ the main output current flow. 3 © Unitec New Zealand

4. JFET construction and symbol 4 © Unitec New Zealand

5. N channel JFET Depletion Layer Biasing 5 © Unitec New Zealand

6. Typical JFET characteristic I-V curves 6 © Unitec New Zealand

7. Biasing in the Active (amplifier) Region 7 © Unitec New Zealand

8. 3 MODES – CS compares to CE for BJT 8 © Unitec New Zealand

9. JFET Amplifier- class A 9 © Unitec New Zealand

10. MOSFET – Insulated Gate Extremely high Input Resistance (MΩ) – very senstive Vulnerable to damage if high static charge builds on gate PMOS and NMOS each available in 2 types 10 © Unitec New Zealand

11. MOSFET structure and Symbol 11 © Unitec New Zealand

12. MOSFET construction and bias 12 © Unitec New Zealand

13. Depletion-mode MOSFET (Normally Closed ) 13 © Unitec New Zealand

14. Enhancement-mode MOSFET (normally off) 14 © Unitec New Zealand

15. Enhancement-mode MOSFET characteristic 15 © Unitec New Zealand

16. Enhancement-mode MOSFET classA Amplifier Inverting amplifier 16 © Unitec New Zealand

17. MOSFET Summary Efficient Low Power consumption (CMOS logic gates) 17 © Unitec New Zealand

18. MOSFET as SWITCH 18 © Unitec New Zealand

19. MOSFET switch Bias 19 © Unitec New Zealand

20. MOSFET Switch Example The faster we turn FET on/off, the less power ‘loss’ Simple resistive load ok, but Inductive or Capacitive loads require protection (Flywheel Diodes) 20 © Unitec New Zealand

21. MOSFET Switches Summary 21 © Unitec New Zealand

22. MOSFET switch example 22 © Unitec New Zealand

23. Simple Motor Control (On/Off) 23 © Unitec New Zealand

24. P channel Switch 24 © Unitec New Zealand

25. Complementary CMOS Motor Control 25 © Unitec New Zealand

26. FET summary 26 © Unitec New Zealand

27. FET chart 27 © Unitec New Zealand

28. FET compared to BJT 28 © Unitec New Zealand