The structures of these devices are similar to their electrical analog in terms of doping. There are various circuit symbols of the photoresistor. Required fields are marked *. CDMA vs GSM, ©RF Wireless World 2012, RF & Wireless Vendors and Resources, Free HTML5 Templates, Active motion sensor vs passive motion sensor. The photodiode uses ordinary PN junction diode which has two terminals namely cathode and anode. • When the light falls on the surface of the disc, resistance between the leads diminish (or reduce). • It represents equal resistance in both the directions and Saturation voltage of phototransistor is the voltage drop between collector and emitter, which seldom exceeds Light is an electromagnetic radiation with a much shorter wavelength and higher frequency than radio waves. ordinary bipolar transistor. 0.5V. Figure-2 above depicts circuit symbol and NPN phototransistor L14G2. « Reply #5 on: March 20, 2009, 08:17:31 AM » It takes me to a question, if i want to calculate resistor needed for photodiode, can I use the same method as photoresistor as described in the tutorial? The photodiode is used in solar power plant, in a light meter, etc. ➨Photodiode is more responsive to incident light than phototransistor. It is a type of PN-junction diode which generates electric current when light or photon is incident on their surface. • Photodiode consists of a normal p-n junction housed in a small enclosure which a ➨Photodiodes pass less current compare to phototransistor. The working of the photodiode depends on the intensity of light strike on it. The collector region of the phototransistor is large as compared to the ordinary transistor because it is made up of heavy diffuse semiconductor material. The circuit diagram of the photodiode is shown in the figure below. The phototransistor generates current whereas the photodiode produces both the voltage and current. The current constitutes in the diode are directly proportional to the intensity of light absorb it. Moreover photodiode consumes less Difference between SISO and MIMO Effective resistance varies with applied voltage. It is similar to photodiode controlling an If used in this way,connection to base terminal is not needed. • It is a transistor controlled by exposure to light. Introduction: Phototransistors and photodiodes are analogs of regular transistors and diodes. It covers advantages and disadvantages of photoresistor and phototransistor. ➨Photodiode has linear response over much wider range of light than phototransistor. ➨Phototransistor is used as solid state switch unlike photodiode. FDMA vs TDMA vs CDMA Whereas, the phototransistor uses the transistor for the conversion of light energy into an electrical current. This generated leakage current is later amplified. It can be used to generate variable voltage. The resistance of a photoresistor decreases with increasing incident light intensity falling on it. When the light incident at the base of an NPN transistor the base current develops. The photodiode and photodiode both convert the light energy into electrical energy. can be achieved. of light falling on the junction. Here it acts as variable resistor based on No, Photoresistor is sensitive to incident light from anywhere in front of it. As a result of this, extra minority carriers are liberated at the reverse biased CB junction (Collector to Base). • Phototransistor has two leads which connect internally with its collector and emitter (or source and drain in FET). FDM vs TDM ➨Dark current of phototransistor is much higher than photodiode. Hence many of the phototransistors do not have a base lead. But phototransistor is more sensitive as compared to photodiode because of the use of the transistor. The circuit symbol of the photo-transistor is shown in the figure below. Photodiodes have similar structure as a regular diode, where a p-n, p-i-n, or similar doping profile is used in the device. The photodiode is a semiconductor device which converts the light’s energy into an electrical current. Few of these devices are moulded in transparent plastic cases with convex. As we know both are photocells. The photodiode is a type of semiconductor diode which converts the light into the electric current. • In the absence of light, bipolar phototransistor permits leakage between collector and emitter of 100 nA or less. Difference between TDD and FDD The photodiode works in both the forward as well as reversed biased whereas the phototransistor work in forward biasing.The emitter of the phototransistor is negative as compared to the collector region. electrons and holes. Difference between SC-FDMA and OFDM it remains same. from smaller one (5 mm in diameter) to larger one (25 mm in diameter). One of the applications of photoresistor is shown in the following circuit. Yes, Photodiode is sensitive to incident light from particular direction and insensitive from other directions. CDMA vs GSM, ©RF Wireless World 2012, RF & Wireless Vendors and Resources, Free HTML5 Templates, Active motion sensor vs passive motion sensor. it can be used either with AC or DC. Hence photodiode is used for battery powered devices requiring less This is result of light energy which breaks the bonds in the crystal lattice of the semiconductor producing When exposed to light, it conducts upto 50mA. It is a special designs transistor which has a light-sensitive base region. This type of diode is also called photo-detector or light sensor. Figure depicts photodiode symbol. Introduction: As we know both are photocells. • It is a disc shaped component with two leads as shown in the figure-1. Resistance varies more with temperature. Effective resistance varies less with temperature. The phototransistor is a two or three terminal semiconductor device which converts the light energy into an electric current or voltage.


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