Obtain an expression for anode current $IA$ when gate is applied with $IG$.

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[!TLDR]

With $I_K=I_A+I_G$ , the two-transistor model gives $I_A=\dfrac{\alpha_2 I_G+(I_{co1}+I_{co2})}{1-(\alpha_1+\alpha_2)}$ .

Using the two-transistor equivalent of the SCR (pnp transistor $T_1$ with gain $\alpha_1$ and npn transistor $T_2$ with gain $\alpha_2$ , leakage currents $I_{co1}$ , $I_{co2}$ ), now a gate current $I_G$ is fed into the base of the npn transistor $T_2$ (the p-base). The cathode current is then

I_K=I_A+I_G

The collector currents are:

I_{C1}=\alpha_1 I_A+I_{co1}

I_{C2}=\alpha_2 I_K+I_{co2}=\alpha_2 (I_A+I_G)+I_{co2}

The anode current is the sum of the two collector currents:

I_A=I_{C1}+I_{C2}=\alpha_1 I_A+I_{co1}+\alpha_2 (I_A+I_G)+I_{co2}

Collecting the $I_A$ terms:

I_A-(\alpha_1+\alpha_2)I_A=\alpha_2 I_G+I_{co1}+I_{co2}

I_A\,[1-(\alpha_1+\alpha_2)]=\alpha_2 I_G+(I_{co1}+I_{co2})

Therefore

$I_A=\frac{\alpha_2 I_G+(I_{co1}+I_{co2})}{1-(\alpha_1+\alpha_2)}$ …

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Q.Obtain an expression for anode current $I_A$ when gate is applied with $I_G$ .

Concept understanding — Silicon Controlled Rectifier (SCR): Construction and Two-Transistor Analysis

Q.Obtain an expression for anode current IAI_AIA​ when gate is applied with IGI_GIG​.

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Q.Obtain an expression for anode current $I_A$ when gate is applied with $I_G$ .

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