We have seen in a previous experiment that the resistance of both a photodiode and a phototransistor changes as the intensity of the light hitting the device. PHOTOTRANSISTOR. Part Number: WP3DP3BT. Features. ○ Mechanically and spectrally matched to the infrared emitting. LED lamp. ○ Blue transparent lens. FUNDAMENTAL PHOTODIODE CIRCUITS. Figures 1 and 2 show the fundamental photodiode circuits. The circuit shown in Figure 1 transforms a photo -.
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Phototransistors are photodiode-amplifier combinations integrated within a phototransistor can be viewed as a photodiode whose output. Phototransistor and IRED Part Number Index. Phototransistor Part . Phototransistors are solid state light detectors that possess internal gain. This makes them. The phototransistor has a light sensitive collector to base junction. A lens is used in a transistor package to expose base to an incident light. When no light is.
The Phototransistors are manufactured in the similar way by which normal transistor is manufactured, the only difference is the area of the base and collector region in case of phototransistors is quite large as compared to the normal transistor. The above equations shown that the collector current is directly proportional to the current base leakage current, i. And the collector current becomes. The light enters into the base region of phototransistor generates the electron-hole pairs. The cut-off region and saturation region can be used to operate the transistor as the switch. Log In Sign Up.
This is because the more the light falls on the phototransistor the more current it will generate. The collector and base region are formed by the techniques of ion-implantation and diffusion. The transistor which were used earlier was made of semiconductor material such as Germanium and Silicon and the resulting structure becomes a homogeneous material consist of either Silicon or Germanium.
On the contrary, contemporarily, phototransistors are made up of Group-III and Group-V materials such as GaAs Gallium Arsenide in such a way that gallium and arsenide, each of these are used on either side of the transistor. The resulting structure becomes heterogeneous in nature.
This type of structure is used widely because the conversion efficiency increases several times as compared to the conversion efficiency of the homogenous transistor.
The output of the phototransistor is taken from the emitter terminal and the light rays are allowed to enter the base region.
The magnitude of the photocurrent generated by the phototransistor depends on the light intensity of the light falling on the transistor. It can be of three terminals or two terminals we can omit base as per our requirement.
The above equations shown that the collector current is directly proportional to the current base leakage current, i. The phototransistor is made up of semiconductor material.
The base of the phototransistor would only be used for biasing the transistor. In case of NPN transistor , the collector is made positive concerning emitter, and in PNP, the collector is kept negative.
The light enters into the base region of phototransistor generates the electron-hole pairs. The movement of electrons under the influence of electric field causes the current in the base region. The base current injected the electrons in the emitter region.
The major drawback of the phototransistor is that they have low-frequency response. The construction of the phototransistor is quite similar to the ordinary transistor.
Earlier, the germanium and silicon are used for fabricating the phototransistor. The small hole is made on the surface of the collector-base junction for placing the lens.
The lens focuses the light on the surface. Nowadays the transistor is made of a highly light effective material like gallium and arsenides.
The emitter-base junction is kept at forward biased, and the collector-base junction is at the reverse biased. When no light falls on the surface of the transistor, the small reverse saturation current induces on the transistor. The reverse saturation current induces because of the few minority charge carriers. The light energy falls on the collector-base junction and generates the more majority charge carrier which adds the current to the reverse saturation current.
The graph below shows the magnitude of current increases along with the intensity of light. The photodiode and phototransistor both convert the light energy into the electrical energy. But the phototransistor is mostly preferred over the photodiode because of their following advantages.
The response time of the photodiode is much higher than the phototransistor. The output current of the photodiode is in microamperes, and it can switch on or off in nanoseconds.
While the response time of the phototransistor is in microseconds and it provides current in milliamperes. In photodarlington, the two transistor connected back to back through the base shown in the figure below.
In this arrangement, the phototransistor induces much higher power, i. The photodarlington transistor has large switching time.
The devices are used in the integrated amplifier and in the photosensitive SCRs amplifier etc. Your email address will not be published.