際際滷

際際滷Share a Scribd company logo

Transistors - JFET, MOSFET, UJT & 555 Timer

Dhivya Ramachandran
Dhivya Ramachandran

This document discusses different types of field effect transistors (FETs), including their basic construction and operation. It provides details on junction FETs (JFETs) and metal-oxide-semiconductor FETs (MOSFETs), as well as depletion and enhancement MOSFETs. The document also covers the drain and transfer characteristics of enhancement MOSFETs. Finally, it describes the working and applications of relaxation oscillators using unijunction transistors (UJTs), including their voltage-current characteristics and use in timing circuits.

1 of 22
Field Effect Transistor Unit II
FET The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs are devices with three terminals: source gate and Drain The Field Effect Transistor, FET, is a three terminal active device that uses an electric field to control the current flow and it has a high input impedance which is useful in many circuits.
Types There are two types of field-effect transistors, The Junction Field-Effect Transistor (JFET) and The Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) or Insulated-Gate Field-Effect Transistor (IGFET).
FET
n- Channel and p- Channel
Comparison
V-I or Transfer Characteristics
V-I or Drain Characteristics
Transfer Characteristics
Comparison between FET and BJT SL No FET BJT 1 Unipolar Device Bipolar Device 2 Voltage Controlled Device Current Controlled Device 3 High Input Resistance Few M-ohms Low Input Resistance Few K-ohms 4 TCR - Negative TCR - Positive 5 No Minority carrier Storage effect high switching Speeds and Cutoff frequencies Suffers Minority carrier Storage effect Lower switching Speeds and Cutoff frequencies 6 Less Noisy More Noisy 7 Simpler to Fabricate Difficult to Fabricate 8 Immune to radiation excellent signal chopper Susceptible to radiation stability is disturbed 9 Lower Gain BW Higher Gain BW 10 Susceptible to overload required spl handling during installation Does not require spl handling during installation
MOSFET MOSFET Two Basic Types Depletion Type D-MOSFET Enhancement Type E-MOSFET Difference Difference in Construction
D-MOSFET Gate to Source Voltage - Negative
E-MOSFET Positive Gate to Source Voltage
Drain & Transfer Characteristics of E-MOSFET
Uni Junction Transistor (UJT)
UJT Working = 巨 + = 1000 巨
V-I Characteristics of UJT
Applications of UJT Trigger Device for SCRs and TRIACs Non-Sinusoidal Oscillators Saw-Tooth generators Timing circuits
Relaxation Oscillator An oscillator is a device that produces a waveform by its own, without any input. Though some dc voltage is applied for the device to work, it will not produce any waveform as input. The UJT relaxation oscillator is called so because the timing interval is set up by the charging of a capacitor and the timing interval is ceased by the rapid discharge of the same capacitor. In electronics a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave.
This waveform depends generally upon the charging and discharging time constants of a capacitor in the circuit.
Relaxation Oscillator - Construction Construction: The emitter of UJT is connected with a resistor and capacitor. The RC time constant determines the timings of the output waveform of the relaxation oscillator. Both the bases are connected with a resistor each. The dc voltage supply VBB is given.
Relaxation Oscillator - Working Working: Initially, the voltage across the capacitor is zero. The UJT is in OFF condition. The resistor R provides a path for the capacitor C to charge through the voltage applied. V=V0(1et/RC) The capacitor usually starts charging and continues to charge until the maximum voltage VBB. But in this circuit, when the voltage across capacitor reaches a value, which enables the UJT to turn ON (the peak voltage) then the capacitor stops to charge and starts discharging through UJT. Now, this discharging continues until the minimum voltage which turns the UJT OFF (the valley voltage). This process continues and the voltage across the capacitor, when indicated on a graph, the following waveform is observed. Relaxation oscillators are widely used in function generators, electronic beepers, SMPS, inverters, blinkers, and voltage controlled oscillators

More Related Content

Transistors - JFET, MOSFET, UJT & 555 Timer

  • 2. FET The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs are devices with three terminals: source gate and Drain The Field Effect Transistor, FET, is a three terminal active device that uses an electric field to control the current flow and it has a high input impedance which is useful in many circuits.
  • 3. Types There are two types of field-effect transistors, The Junction Field-Effect Transistor (JFET) and The Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) or Insulated-Gate Field-Effect Transistor (IGFET).
  • 4. FET
  • 5. n- Channel and p- Channel
  • 7. V-I or Transfer Characteristics
  • 8. V-I or Drain Characteristics
  • 10. Comparison between FET and BJT SL No FET BJT 1 Unipolar Device Bipolar Device 2 Voltage Controlled Device Current Controlled Device 3 High Input Resistance Few M-ohms Low Input Resistance Few K-ohms 4 TCR - Negative TCR - Positive 5 No Minority carrier Storage effect high switching Speeds and Cutoff frequencies Suffers Minority carrier Storage effect Lower switching Speeds and Cutoff frequencies 6 Less Noisy More Noisy 7 Simpler to Fabricate Difficult to Fabricate 8 Immune to radiation excellent signal chopper Susceptible to radiation stability is disturbed 9 Lower Gain BW Higher Gain BW 10 Susceptible to overload required spl handling during installation Does not require spl handling during installation
  • 11. MOSFET MOSFET Two Basic Types Depletion Type D-MOSFET Enhancement Type E-MOSFET Difference Difference in Construction
  • 12. D-MOSFET Gate to Source Voltage - Negative
  • 13. E-MOSFET Positive Gate to Source Voltage
  • 14. Drain & Transfer Characteristics of E-MOSFET
  • 16. UJT Working = 巨 + = 1000 巨
  • 18. Applications of UJT Trigger Device for SCRs and TRIACs Non-Sinusoidal Oscillators Saw-Tooth generators Timing circuits
  • 19. Relaxation Oscillator An oscillator is a device that produces a waveform by its own, without any input. Though some dc voltage is applied for the device to work, it will not produce any waveform as input. The UJT relaxation oscillator is called so because the timing interval is set up by the charging of a capacitor and the timing interval is ceased by the rapid discharge of the same capacitor. In electronics a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave.
  • 20. This waveform depends generally upon the charging and discharging time constants of a capacitor in the circuit.
  • 21. Relaxation Oscillator - Construction Construction: The emitter of UJT is connected with a resistor and capacitor. The RC time constant determines the timings of the output waveform of the relaxation oscillator. Both the bases are connected with a resistor each. The dc voltage supply VBB is given.
  • 22. Relaxation Oscillator - Working Working: Initially, the voltage across the capacitor is zero. The UJT is in OFF condition. The resistor R provides a path for the capacitor C to charge through the voltage applied. V=V0(1et/RC) The capacitor usually starts charging and continues to charge until the maximum voltage VBB. But in this circuit, when the voltage across capacitor reaches a value, which enables the UJT to turn ON (the peak voltage) then the capacitor stops to charge and starts discharging through UJT. Now, this discharging continues until the minimum voltage which turns the UJT OFF (the valley voltage). This process continues and the voltage across the capacitor, when indicated on a graph, the following waveform is observed. Relaxation oscillators are widely used in function generators, electronic beepers, SMPS, inverters, blinkers, and voltage controlled oscillators