Special purpose diodes

Special purpose diodes which includes:
Zener diodes
Vericap / Varactor diodes/variable capacitance diode
Optical diodes (i) light emitting diode (LED) (ii) photo diode
Schottky diode
Pin diode
Tunnel diode
Step recovery diode/snap diode
Laser diode
Impatt diode
Gunn diode
Constant-current diodes

1. SPECIAL - PURPOSE DIODES Presenting By: Submitted To: A dnan Q ayum Lecturer Engr. Iqbal Munir 13SWTBTECE156 Govt. College of Technology B.Tech Electrical, Ist year Swat. [email protected]

2. It includes the followings: Schottky diode Pin diode Tunnel diode Step recovery diode/snap diode Laser diode Impatt diode Gunn diode Constant-current diodes Zener diodes Vericap / Varactor diodes/variable capacitance diode Optical diodes ( i ) light emitting diode (LED) (ii) photo diode Other types of diodes

3. Zener Diodes A Zener diode is a type of diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". The device was named after Clarence Zener, who discovered this electrical property.

4. Symbol

5. Zener diode in a circuit

6. ZENER DIODE APPLICATIONS The zener diode is often used as a type of voltage regulator for providing stable stable reference voltages.

7. Varactor Diodes Vericap, Varactor or variable capacitance diode (operate in reverse bias) is a type of diode whose capacitance varies as a function of the voltage applied across its terminals. Vericap circuit symbol

8. Basic Operation

9. An Application A major application of varactors is in tuning circuits. For example, electronic tuners in TV and other commercial receivers utilize varactors. When use in a resonant circuit, the varactor act as variable capacitor, thus allowing the resonant frequency to be adjusted by a variable voltage level, where the varactor diode provides the total variable capacitance in the parallel resonant band-pass filter

10. Optical Diodes Two types Light Emitting Diode (LED) Photo Diode Light Emitting Diode (LED): operates in forward biased, The light-emitting diode (LED) emits photons as visible light. It’s purpose is for indication and other intelligible displays. Various impurities are added during the doping process to vary the color output.

11. Symbol

12. Light Emission in LED

13. Applications Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning. Illumination where light is reflected from objects to give visual response of these objects. Measuring and interacting with processes involving no human vision. Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light

14. The Photodiode A  photodiode  is a semiconductor device that converts light into current. The current is generated when photons are absorbed in the photodiode. A small amount of current is also produced when no light is present. Photodiodes may contain optical filters, built-in lenses, and may have large or small surface areas. Photodiodes usually have a slower response time as its surface area increases. The common, traditional solar cell used to generate electric solar power is a large area photodiode. A photodiode is designed to operate in reverse bias.

15. Symbol

16. Principle of operation A photodiode is a p-n junction structure. When a photon of sufficient energy strikes the diode, it creates an electron, hole pair. This mechanism is also known as the inner photoelectric effect. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is produced. The total current through the photodiode is the sum of the dark current (current that is generated in the absence of light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device

17. Operation of a Photodiode

18. Other types of Diodes Current Regulator Diode It keeps constant current. In Forward biased With specific range of voltage i.e. from 1.5 V to 6 V. Symbol

19. Schottky diode A solid-state diode having a metal-semiconductor junction, used in fast switching applications.

20. A  PIN diode  is a diode with a wide, lightly doped 'near' intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region

21. Step recovery diode  ( SRD ) is a semiconductor junction diode having the ability to generate extremely short pulses. The step recovery diode or SRD is able to be used as a microwave radio frequency generator and pulse sharpener. Although used in more specialist applications, the SRD is nevertheless a very useful component that is capable of some very high levels of performance. As such it is a very useful tool in the armoury of the RF design engineer to be used when the occasion requires.

22. The tunnel diode exhibits a special characteristics known as negative resistance. This features makes it useful in oscillator and microwave amplifier applications. Negative resistance  is a property of some electric circuits where an increase in the current entering a port results in a decreased voltage across the same port. This is in contrast to a simple ohmic resistor, which exhibits an increase in voltage under the same conditions

23. The Laser Diode A laser diode is electrically a P- i -n diode. The active region of the laser diode is in the intrinsic (I) region, and the carriers, electrons and holes, are pumped into it from the N and P regions respectively   laser diode , or  LD , is an electrically pumped semiconductor laser in which the active medium is formed by a p-n junction of a semiconductor diode similar to that found in a light-emitting diode. The laser diode is the most common type of laser produced. Laser diodes have a very wide range of uses that include, but are not limited to, fiber optic communications, barcode readers, laser pointers, CD/DVD/ Blu -ray reading and recording, laser printing, scanning and increasingly directional lighting sources.

24. Laser diode (LD) Symbol

25. x Thank You