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How a PLL works ? Consider VCO operating without input signal at free-running frequency fr and input signal of frequency fIN increasing from zero is applied to the…

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Programmable UJT (PUT). Programmable unijunction transistor or PUT is a close relative of the thyristor family. Its has a four layered construction just like the thyristors and have…

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UJT relaxation oscillator UJT relaxation oscillator is a type of RC ( resistor-capacitor) oscillator where the active element is a UJT (uni-junction transistor). UJT is an excellent switch…

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The diacs, because of their symmetrical bidirectional switching characteristics, are widely used as triggering devices in triac phase control circuits em­ployed for lamp dimmer, heat control, universal motor…

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Introduction to Diac-Operation and Construction A diac is an important member of the thyristor family and is usually employed for triggering triacs. A diac is a two-electrode bidirectional…

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Applications of Triac Next to SCR, the triac is the most widely used member of the thyristor family. In fact, in many of control applications, it has replaced…

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Characteristics of  Triac Typical V-I characteristics of a triac are shown in figure. The triac has on and off state characteristics similar to SCR but now the char…

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The ability of an SCR to control large currents to a load by means of small gate current makes the device very useful in switching and control applications.…

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How to protect an SCR using protection circuits ? SCRs are sensitive to high voltage, over-current, and any form of transients. For satisfactory and reliable operation they are…

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Current ratings of an SCR The current carrying capability of an SCR is solely determined by the junction temperature. Except in case of surge currents, in no other…

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SCR Voltage Ratings (i) Breakover Voltage. The minimum forward voltage, when the gate is open, at which SCR starts conducting heavily (that is turned-on) is called the breakover…

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Turning-off Methods of an SCR As already mentioned in previous blog post, once the  SCR is fired, it remains on even when triggering pulse is removed. This ability…

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