UJT Relaxation Oscillator

jojo August 13, 2017 8 Comments
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 with switching times in the order of nano seconds. It has...
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SCR Triggering using UJT

jojo September 17, 2009 2 Comments
How to trigger an SCR using UJT ? One common application of the uni junction transistor is the triggering of the other devices such as the SCR, triac etc. The basic elements of such a triggering circuit are shown...
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SCR Current Ratings

jojo September 14, 2009 No Comments
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 case the junction temperature is permitted to exceed the permissible value....
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Voltage ratings of an SCR

jojo September 14, 2009 3 Comments
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 voltage. To specify this value, the gate is in the open-circuit...
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Ratings and Specifications of an SCR

jojo September 14, 2009 No Comments
SCR-Ratings and Specifications The performance of an SCR is affected by the junction temperature, because of change in carrier densities in the four layers and the junction temperature naturally depends upon the internal power losses of the device and...
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SCR Turning OFF methods

jojo September 14, 2009 No Comments
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 of the SCR to remain on even when gate current is...
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Turn on methods of an SCR

jojo September 14, 2009 3 Comments
How to turn ON an SCR ? As mentioned earlier, the SCR can be switched on either by increasing the forward voltage beyond forward break over voltage VFB0 or by applying a positive gate signal when the device is...
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Dynamic Characteristics of an SCR

jojo September 11, 2009 1 Comment
Turn-on and turn-off characteristics of an SCR are called the dynamic characteristics of the SCR. (a)    Turn-On Character­istic. The turn-on time charac­teristic shows the variation of current and voltage during turn-on. Turn-on time is defined as the time from the...
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SCR-Volt-ampere-Characteristics

jojo September 11, 2009 7 Comments
As already mentioned, the SCR is a four-layer device with three terminals, namely, the anode, the cathode and the gate. When the anode is made positive with respect to the cathode, junctions J1 and J3 are forward biased and...
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SCR-Principle of Operation

jojo September 10, 2009 23 Comments
How an SCR works?-Principle of Operation SCR Working Principle The SCR is a four-layer, three-junction and a three-terminal device and is shown in fig.a. The end P-region is the anode, the end N-region is the cathode and the inner...
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