Question

how do to compute voltage current and resistance of UJT, dc motor and strain gauge

Answer 1

Unijunction Transistor:- Although a unijunction transistor is not a thyristor, this device can trigger large thyristors with a pulse at base B1. A unijunction transistor is composed of a bar of N-type Silicon having a P-type connection in middle. The connection at the end of the bar are known as base B1 and B2, the P-type mid point is the emitter. With the emitter disconnected, the total resistance R_BBO, a datasheet item, is the sum of R_B1 and RB2

the above figure a,b,c are showing the symbolic representation of the unijunction transistor.

UJT is another solid state three terminal device that can be used in gate pulse, timing circuits and trigger generator applications to switch and control either thyristors and triac’s for AC power control type applications.

Like diodes, unijunction transistors are constructed from separate P-type and N-type semiconductor materials forming a single (hence its name Uni-Junction) PN-junction within the main conducting N-type channel of the device.

Although the Unijunction Transistor has the name of a transistor, its switching characteristics are very different from those of a conventional bipolar or field effect transistor as it can not be used to amplify a signal but instead is used as a ON-OFF switching transistor. UJT’s have unidirectional conductivity and negative impedance characteristics acting more like a variable voltage divider during breakdown.

The Unijunction emitter current vs voltage characteristic curve shows that as V_E increases, current I_E increases up I_P at the peak point. Beyond the peak point, current increases as voltage decreases in the negative resistance region. The voltage reaches a minimum at the valley point. The resistance of R_B1, the saturation resistance is lowest at the valley point.

the above figure of V-I characteristics shown is the graph between the voltage and current in which the graph is gradually increasing and got a peak value then is starts decreasing towards the valley point and then gradually going towards the saturation point.

In the DC motor to compute the voltage and current we use Ohms law as usual we use for all

to find the voltage (V) , V = I X R

to find the current (I), I = V/R

to find the resistance (R), R = V/I..

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