Electronic – Circuit Analysis With Non-Ideal Diodes

circuit analysisdiodes

I have seen how to do circuit analysis with ideal diodes, that is replace forward-biased diodes with connections and replace reverse-biased diodes with gaps. But the problem is that I want to know how to analize real circuits that contain non-ideal diodes. How do I do so?

I need a few leads.

EDIT

See comments.

Best Answer

If you don't want the simplifications, you have to fall back to the general model of a diode:

$$ I = I_o \left( e^{\frac{eV}{nkT}}-1 \right) $$

This equation relates the diode current to the diode voltage (it's V-I characteristic)

  • Io - is the diode reverse saturation current
  • k - Boltzmann's constant = 1.38e-23 Joules per Kelvin
  • T - Analysis temperature (Kelvin)
  • e - Magnitude of electric charge
  • n - Ideality factor (for silicon diodes, n=2 for small currents and approaches n=1 for large currents; in theory should always = 1)

You can now solve your circuit via the system of equations that it produces. Although you now have continuous V-I functions to describe your elements, a closed-form solution is not always guaranteed to exist.

It is often necessary to use an iterative solution technique such as Newton-Raphson to approximate/approach the answer. This is what SPICE solvers do in the general case... and why they ask you for initial conditions (which can dramatically speed up the solution time).

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