1 / 21

Chapter 5

Chapter 5. Special Applications Diodes. Varactor Diodes. Varactor diodes have relatively high junction capacitance when reverse biased. Varactor Junction Capacitance. The width of the varactor depletion layer (W d ) is controlled by the junction reverse bias. Varactor Bias vs. Capacitance.

bell
Download Presentation

Chapter 5

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 5 Special Applications Diodes

  2. Varactor Diodes • Varactor diodes have relatively high junction capacitance when reverse biased.

  3. Varactor Junction Capacitance • The width of the varactor depletion layer (Wd ) is controlled by the junction reverse bias.

  4. Varactor Bias vs. Capacitance Capacitance decreases as the magnitude of reverse bias increases.

  5. Varactor Specifications • Diode capacitance temperature coefficient (TCC) – The amount by which varactor capacitance changes with changes in temperature. • Temperature has little effect on the capacitance rating of most varactors. • Diode capacitance (Ct ) – The rated value (or range) of C for a varactor at a specific value of VR. • Capacitance ratio (CR ) – The factor by which C changes from one specified value of VR to another.

  6. Varactor-Tuned LC Circuit • The varactor acts as a voltage-controlled capacitance. • The R2 setting is varied to adjust varactor capacitance. • The varactor capacitance determines (in part) the resonant frequency of the LC circuit.

  7. Transient Suppressors • Transient suppressors are zener diodes with extremely high surge-handling capabilities. • Normally used to protect circuits from power line surges.

  8. Transient Suppressor Specifications • Peak power dissipation (PPK) – The amount of surge power that the suppressor can dissipate. • Working peak reverse voltage (VRWM) – The maximum reverse voltage that will not drive a transient suppressor into its reverse breakdown (zener) region of operation. • Breakdown voltage (VBR) – The reverse voltage that will drive a transient suppressor into its reverse breakdown (zener) region of operation. • Clamping voltage (VC ) – The rated reverse voltage across a conducting transient suppressor.

  9. Surge Protection Circuits

  10. Constant-Current Diodes • A constant-current diode maintains a relatively constant device current over a wide range of forward operating voltages. • Also referred to as a current regulator diode. • The current regulator diode has its own schematic symbol.

  11. Constant-Current Diode Forward Operation Curves

  12. Constant-Current Diode Specifications • Peak operating voltage (POV) – The maximum allowable value of VF. • Maximum limiting voltage (VL ) – The voltage at which the diode begins to limit current. • Regulator current (IP ) – The rated forward current at component voltages between VL and POV.

  13. Tunnel Diodes • Tunnel diodes are heavily-doped, making them suitable for use in high-frequency communications circuits. • They are commonly used in ultra-high frequency (UHF) circuits. UHF circuits operate in the range of 100 MHz to 3 GHz. • Tunnel diodes exhibit a property referred to as negative resistance.

  14. Negative Resistance • Negative resistance – A term used to describe any device with current and voltage values that are inversely related. • The negative resistance portion of the tunnel diode curve falls between its peak and valley voltage and current values.

  15. Tunnel Diode Oscillator • Oscillator – A circuit that converts dc to ac. An ac signal generator. • The tunnel diode oscillator is also referred to as a negative resistance oscillator.

  16. Schottky Diodes • Schottky diode – A high-speed diode with very little junction capacitance. • Also known as Schottky-barrier, hot-carrier, or surface-barrier diodes. • High frequency characteristics make these diodes well suited for high-speed switching applications. • The metal-semiconductor junction provides little capacitance, allowing higher frequency operation of the component.

  17. Schottky Diode Symbol & Curve

  18. PIN Diodes • The PIN diode has three semiconductor materials. • A p-type anode • An n-type cathode • An intrinsic (pure) semiconductor layer.

  19. Pin Diode Capacitance

  20. PIN Diode Forward Characteristics • The forward operating curve shows that: • Conduction begins at a value of VF > 0 V. • The PIN diode has no specific knee voltage (voltage at which the device increases abruptly).

  21. Step-Recovery Diodes • Step-recovery diode – A heavily doped diode that has an ultrafast switching time. • The ends of the component are doped more heavily than the area near the junction. This reduces the time required for the device to switch from off to on, and vice versa.

More Related