SCR Triggering Circuit by Synchronized UJT & IC 785:

One application that is typical of Unijunction transistor could be the triggering concerning the other products like the SCR, triac etc.

The basic the different parts of such a triggering circuit are shown in figure. The resistor RE is plumped for which means that your load line predicated on RE passes through the product attribute in to the opposition that is negative, that is, towards the right regarding the top point but to your left associated with valley point, as shown in fig.1-7. The device cannot change on in the event that load line doesn't pass to your right from the point that is top.

For ensuring turn-on of UJT

RE < VBB – Vp¬ / IP………………………………………………1.3

This is often established as below look at the peak point at which,

IRE = Ip and VE = VP……………………………………………...1.4

(the equality IRE = protocol that is internet is valid because the charging you current of capacitor, only at that instant is zero, that is, the capacitor, as of this instant that is specific is changing from the asking state to a discharging state).Then,

VE = VBB – IRE RE …………………………………………..1.5

RE MAX that is( = VBB – VE¬ / IRE = VBB – Vp¬ / IP…………………….1.6

At the valley point, V

IE = IV and VE = VV so

VE = VBB – IRE RE………………………………………………1.7

Therefore RE (MIN) = VBB – VE / IRE = VBB – VV / IV and sometimes even for ensuring turn-off.

RE > = VBB – VV / IV

Therefore, the product range of resistor RE is offered as

VBB – VP / IP >RE > VBB – VV / IV……………………………….1.8

The resistor R is plumped for little enough so that you can ensure that SCR isn't fired up by voltage VR whenever emitter terminal E is IE or open = 0

The voltage VR = RVBB/R + RBB for open-emitter terminal.

The capacitor C determines enough time period that is best between triggering pulses plus the time duration of each pulse. By varying RE, we could replace the time that is best constant RE C and alter the point at which the UJT fires. This gives us to modify the conduction angle regarding the SCR, this implies the control of load current.