Optocoupler Circuit Operation: An Optocoupler Circuit Operation (optoelectronic coupler) is essentially a photo-transistor and an LED combined in one package. Figure 20-35(a) and (b) shows the typical circuit and terminal arrangement for one such device contained in a DIL plastic package. When current flows in the LED, the emitted light is directed to the phototransistor, …
Photodarlington Working: The Photodarlington Working shown in (Fig. 20-33) consists of a phototransistor connected in Darlington arrangement with another transistor. This device is capable of producing much higher output currents than a phototransistor, and so it has a greater sensitivity to illumination levels than either a phototransistor or a photodiode. With the additional transistor involved, …
Phototransistor Working: A Phototransistor Working is similar to an ordinary BJT except that its collector base junction is constructed like a photodiode. Instead of a base current, the input to the transistor is in the form of illumination at the junction. Construction and Working of Phototransistor: Consider an ordinary BJT with its base terminal open-circuited, …
Solar Energy Conversion Diagram: The Solar Energy Conversion Diagram, or solar energy converter, is essentially a large photodiode designed to operate solely as a photovoltaic device and to give as much output power as possible. To provide maximum output current, solar cell surface areas are much larger than those of signal photodiodes, Typical solar cell …
Photodiode Operation and Characteristics: Photodiode Operation – When a pn-Junction is reverse biased, a small reverse saturation current flows due to thermally generated holes and electrons being swept across the junction as minority charge carriers. Increasing the junction temperature generates more hole-electron pairs, and so the minority carrier (reverse) current is increased. The same effect …
Photoconductive Cell Construction and Working: Photoconductive Cell Construction and Working – Light striking the surface of a material can provide sufficient energy to cause electrons within the material to break away from their atoms. Thus, free electrons and holes (charge carriers) are created within the material, and consequently its resistance is reduced. This is known …
LED Seven Segment Display: The arrangement of a LED Seven Segment Display is shown in Fig. 20-6(a). The actual LED devices are very small, so, to enlarge the lighted surface, solid plastic light pipes are often employed, as shown. Any desired numeral from 0 to 9 can be indicated by passing current through the appropriate …
Light Units: The total light energy output, or luminous flux (Φs), from a source can be measured in milliwatts (mW) or in lumens (1m), where 1 Im = 1.496 mW. The luminous intensity (Es) (also termed illuminance) of a Light Units source is defined as the luminous flux density per unit solid angle (or cone) …