## edr1c 3 years ago how to estimate diode bulk resistance from I-V graph?

1. nick67

Hi edr1c, as a rule of thumb you may evaluate the forward diode resistance as: \[R _{F}=\Delta V_{D} / \Delta I_{D}\] taking values from the quasilinear portion of the characteristic

2. edr1c

so by taking 2points above the turn on voltage for the diode, i will get the approximate resistance by taking their gradient?

3. nick67

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4. edr1c

does barrier potential comes into consideration when calculating this resistance? because the previous section asked us to estimate the barrier potential.

5. edr1c

the reason im raising the question is because i obtained a very high value for the resistance. Voltage, V1/V Current, I/mA 0.6 0.92 0.64 1.71 0.68 4.04 0.7 5.81 0.72 8.81 0.74 12.72 0.76 17.86 0.77 20.89 i got around 17ohm by taking the 2nd and 3rd point

6. nick67

Well, if you take points too close to the diode knee you have of course a greater resistance, because it is still going into forward bias; if you take last two points you have a resistance of about 3,3 Ohm; in this region the diode is in its linear zone

7. nick67

As for the barrier potential you could apply a reverse calculus taking values from last two points; you have there a diode voltage of about 0.76 V and a diode current of about 19 mA. If you subtract the voltage on the bulk resistance from the total diode voltage you can evaluate the barrier potential:\[V _{barrier} = V _{D} - R _{bulk} I _{D}\] that is 0.76 - 3.3 x 0.019 = 0.697 V

8. 911elctronic