4.2.5 Light-Sensitive Diodes

Chapter 4.2.5 Light-Sensitive Diodes

Physics Lecture Notes – Phys 395 Electronics Book
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Physics Lecture Notes – Phys 395 Electronics Book

  • CHAPTER 4. DIODE CIRCUITS69IVa)R fRrRZVZb)IZR ZVZ+IZc)Figure 4.6: a) Current versus voltage of a zener diode, b) schematic symbol for a zener diodeand c) equivalent circuit model of a zener diode in the reverse-bias direction.respond quickly to changes in current (10 MHz). LEDs have applications in optical-fibercommunication and diode lasers. They produce a narrow spectrum of coherent red or infraredlight that can be well collimated.As an electron in the conduction band recombines with a hole in the valence band, theelectron makes a transition to a lower-lying energy state and releases energy in an amountequal to the band-gap energy. Normally the energy heats the material. In an LED thisenergy goes into emitted infrared or visible light.4.2.5Light-Sensitive DiodesIf light of the proper wavelength is incident on the depletion region of a diode while a reversevoltage is applied, the absorbed photons can produce additional electron-hole pairs. Photo-diodes or photocells can receive frequency-modulated light signals. LEDs and photodiodesare often used in optical communication as receiver and transmitter respectively.4.3Circuit Applications of Ordinary DiodesLets briefly discuss some applications of ordinary diodes. For many circuits only the basicdiode effect is of any significance and these circuits can be analyzed under the assumptionthat the diode is an ideal device.4.3.1Power SuppliesBatteries are often shown on a schematic diagram as the source of DC voltage but usuallythe actual DC voltage source is a power supply. A more reliable method of obtaining DC