Question

1. determine the minimum input voltage (v_in) needed to trigger the scr, for the circuit shown below. given: v_gt = 0.75 v, i_gt = 8 ma, i_h = 6.5 ma

a. 3.45 v
b. 8.75 v
c. 0.75 v
d. 6.75 v

Explanation:

Step1: Apply Ohm's law for gate - circuit

The current through the gate - resistor \(R_G\) must reach the gate - trigger current \(I_{GT}\) to trigger the SCR. According to Ohm's law \(V = IR\). The voltage across \(R_G\) is related to the input voltage \(V_{in}\) and the gate - trigger voltage \(V_{GT}\). The current through \(R_G\) is \(I_{GT}\), and \(R_G=1k\Omega = 1000\Omega\), \(V_{GT}=0.75V\).
We know that \(V_{in}-V_{GT}=I_{GT}R_G\).

Step2: Solve for \(V_{in}\)

Rearrange the formula \(V_{in}-V_{GT}=I_{GT}R_G\) to get \(V_{in}=I_{GT}R_G + V_{GT}\).
Substitute \(I_{GT}=8\times10^{- 3}A\), \(R_G = 1000\Omega\) and \(V_{GT}=0.75V\) into the formula.
\[

$$\begin{align*} V_{in}&=(8\times10^{-3}A)\times1000\Omega+ 0.75V\\ &=8V + 0.75V\\ &=8.75V \end{align*}$$

\]

Answer:

B. 8.75 V