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Rampart
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Not the way to determine ac diode impedance.<<In determining the diode dynamic resistance r,where did you get the 0.7V?The 4 mA?
The ac source gives maximum Vm=0.1V,so it is not possible to get 0.7 just from that.The main source is the dc source which gives steady 2V.But the AC source adds as well,does it not?
Yes.<<1. Determine the diode dynamic impedance r = ∂Id/∂Vd at the 2Vdc input level
of the diode when Vac in = 0. Use the standard I-V diode relationship for a junction diode>>
ok why i should take that AC source is 0? In order to use this equation dv/di=R, must i have only the DC source?
r is very nearly always constant and is computed when ac input = 0. r does not vary appreciably with ac voltage if ac current << dc current, here the case.Is it because R is a constant only when the as source is 0? Only when there is a linear relation? Do i get from the graph that AC must not be taken into account? I am just posting some thoughts i have into mind...
That is basically right. Your ac amplitude is << dc voltage at the diode anode so r is always constant.>
2. Then it's a linear problem if you neglect the small changes in r with input ac voltage. The dc diode current and dynaminc impedance do not change significantly with ac input voltage (why?). The diode ac current is determined by r and the 100 ohm resistors.
I take that AC source is 0, because its voltage is too low so that it doesn't really make any difference? That is why in the graph there is a linear relation between id and vd?
I believe the problem wants you to find iac and Idc. iac is determined by including r in your equations, along with the two 100 ohm resistors. Idc is determined by a dc analysis with the input ac voltage = 0. These are basically totally different computations.And now the thing i do not have a clue about.<<The diode ac current is determined by r and the 100 ohm resistors>>.If i regarded AC source is 0, why should i find the ac current? Wouldnt it be
id=idc+iac ~ idc(where idc is the current that is <<produced>> only by the dc source).
Only very slightly. You are to ignore that variation. The reason is that the ac amplitude is << dc input voltage.Do Id and Vd change through time just because of the ac source?
You're welcome!You sir,honestly speaking,made my day.Some things are more clear now and i thank you for that!