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- Thread starter Rampart
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1. Determine the diode dynamic impedance r = ∂I

of the diode when V

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.

Have fun!

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The as 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?

of the diode when V

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?

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...

<<

Have fun!

>>

I take that AC source is 0,because its voltage is too low so that it doesnt really make any difference?That is why in the graph there is a linear relation between id and vd?

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).

Do id and vd change through time just because of the ac source?

I know these questions are many and too simple for most of you,but it is the only way to build myself.

Feel free guys to answer whenever you want and can.

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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 = ∂I_{d}/∂V_{d}at the 2Vdc input level

of the diode when V_{ac 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...

The basic junction diode equation is I

You are trying to find the diode dynamic impedance r about your operating point. Your operating ("bias") point is when the ac input = 0. The bias point is negligibly disturbed with the ac input voltage since ac << dc inputs. AC diode current is a function of r only.

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 iAnd 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).

Electronics is full of circuits where the ac current is 10

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?

- #5

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You sir,honestly speaking,made my day.Some things are more clear now and i thank you for that!!

- #6

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You're welcome!You sir,honestly speaking,made my day.Some things are more clear now and i thank you for that!!

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