Question

In a device $I=40\mu A[e^{V/V_T}-1]$ where $V_T=0.025V$. Find the dynamic resistance when $V=0.5V$

• A. zero
• B. $8\Omega$
• C. $10\Omega$
• D. $30\Omega$
• E. none of these

Answer 1

The correct option is A zero

Current is given as $I=I_S[e^{V/V_T}-1]$ where $I_S=40\mu A$
Thus differentiating it w.r.t $V$, we get $\frac{dI}{dV}=\frac{I_S}{V_T}{e}^{V/V_T}$
or we get dynamic resistance $R=\frac{dV}{dI}=\frac{V_T}{I_S{e}^{V/V_T}}=\frac{0.025}{40\times {10}^{-6}\left[e^{20}\right]}$
$\therefore$ $R=\frac{0.025}{40\times {10}^{-6}\times 5\times {10}^8}\approx 0\Omega$