# Dynamic resistance of diode

1. ## Dynamic resistance of diode

What does it meant by dynamic resistance of the diode....
in what sense it is described as dynamic...
i don't want any quantitative explanation...can anyone tell the physical significance of the term(Dynamic resistance)

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2. ## Re: Dynamic resistance of diode

Hi...

Dynamic resistance of the diode is the resistance for an AC source deppending of the DC polarization of the diode.

The DC polarization determines the dynamic resitance, a high diode DC current is a minimun dynamic resitance because the variation in the curve of diode is more high then less resistance.

If the AC source is aproximated 5mVpp the diode presents a dynamic resistance of Rd=25.9mV/Id
where 25.9mV is a constant and Id y the DC diode current.

The AC source should be small to avoid great changes in Id because:

Id(Total)=Id(AC)+Id(DC) [superposition principle]

Example:

with Id=5mA then Rd=25.9mV/5mA=5.18 Ohms
Id=0.5mA then Rd=25.9mV/0.5mA= 51.8 Ohms

The term Dynamic is because the resistance change arround the working zone of the diode.

I hope that the information evacuates yours doubts.

Ask if he is necessary something more.

Regards from Argentina.

1 members found this post helpful.

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3. ## Re: Dynamic resistance of diode

vavachan,
Dynamic resistance is the slope of the voltage vs current curve of the diode at a particular operating point. It is called the dynamic reistance because it is based on incremental change in voltage diovided by incremental change in current.
Regards,
Kral

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4. ## Re: Dynamic resistance of diode

hi,
let me put some light on the physical side:diode is a non linear device because the current that flows through it is proportional to exponent.rd is the differential resistance of the diode and is determined by the potential difference on the diode. when ac is small dc potential is much higher and constant, therfore we can say that when ac is small the voltage potential of the diode is constant. in that case we can use the model of voltage source and serial resistance rd.

avi.

5. ## Re: Dynamic resistance of diode

Hi
Every element that is modeled in two form by scientists, one macro model, the other micro model; in all fields of knowledge such as mechanics, electronics, etc;
In electronics, when you have a small variation in input signal (as input) of an element (as system), since your system can be modeled for every different situation (bias), so it shows a different behavior to this input signal!
when a specific amount of current flows in your diode, if this current (or input voltage) be changed very little, you may calculate new current or voltage across your diode just estimating your diode as a linear element, so ΔV=(dynamic resistance of the diode)rd . ΔI!
hope to be useful! if you want you can click on "help me" button, it doesn't cost you!

Regards,
SAZ

2 members found this post helpful.

6. ## Re: Dynamic resistance of diode

Let's start by looking at the graph of a diode.

A diode does not conduct until the voltage across it reaches 0.7V. (approximately) After this point the current and the voltage have an exponential relationship.

Now in ac, considering the fact that the variation of V is very small about the DC point, the diode can be regarded as a resistor. Now why? look at the graph of VI for a diode. In this graph, if The change in V is small, (i.e. move a bit about the biase point) the change in I is almost linear and thus a resistor. This is called the dynamic resistance of a diode.

Why is it called dynamic? Because it only appears when there is a change in voltage. i.e. ac.

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7. ## Re: Dynamic resistance of diode

Originally Posted by kronos2k3
Hi...

Dynamic resistance of the diode is the resistance for an AC source deppending of the DC polarization of the diode.

The DC polarization determines the dynamic resitance, a high diode DC current is a minimun dynamic resitance because the variation in the curve of diode is more high then less resistance.

If the AC source is aproximated 5mVpp the diode presents a dynamic resistance of Rd=25.9mV/Id
where 25.9mV is a constant and Id y the DC diode current.

The AC source should be small to avoid great changes in Id because:

Id(Total)=Id(AC)+Id(DC) [superposition principle]

Example:

with Id=5mA then Rd=25.9mV/5mA=5.18 Ohms
Id=0.5mA then Rd=25.9mV/0.5mA= 51.8 Ohms

The term Dynamic is because the resistance change arround the working zone of the diode.

I hope that the information evacuates yours doubts.

Ask if he is necessary something more.

Regards from Argentina.
do you mean that this resistance appears only for ac source...
i think this resistance is called as dynamic because of the change in the resistance
with changee in the current through the diode...is it right
Regards Jerin, from india