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Basics of semiconductor diodes....

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Urmi

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Hi! I need some help understanding some basic concepts of semiconductor diodes...please,please help me by answering a few of myquestions....

1. Why do the static and dynamic resistances of a junction diode vary with the applied voltage?

2. During forward bias,majority carriers in either side move toward the junction....do they cross the junction? If not,how does the current flow through the entire diode?

3. Zener diodes have to tolerate very high power dissipation...how do they recover from the widespread bond-breakages and make themselves fit for reuse after breakdown has taken place?

4. In the breakdown region of a zener diode,the voltage remains constant...now,if we vary the applied voltage from the battery,how does the diode maintain the voltage against the change of current that will be caused?(i.e does the resistance value continuously vary itself?How?)
 

they vary in accordance to the depletion region expansion and contraction

yes the charges cross the junction but become the minority carriers on the other side

if this has helped you please click helped me
 

Thanks,but I need more explanatory answers!! Also,fuuton has not answered my 3rd and fourth questions..please help guys,I have an exam next week!!
 

Urmi said:
Hi! I need some help understanding some basic concepts of semiconductor diodes...please,please help me by answering a few of myquestions....

1. Why do the static and dynamic resistances of a junction diode vary with the applied voltage?

2. During forward bias,majority carriers in either side move toward the junction....do they cross the junction? If not,how does the current flow through the entire diode?

3. Zener diodes have to tolerate very high power dissipation...how do they recover from the widespread bond-breakages and make themselves fit for reuse after breakdown has taken place?

4. In the breakdown region of a zener diode,the voltage remains constant...now,if we vary the applied voltage from the battery,how does the diode maintain the voltage against the change of current that will be caused?(i.e does the resistance value continuously vary itself?How?)

1.) For each non-linear I-V-characteristic both resistances (static/dynamic) are different and depend on the bias condition (the point for the tangent).

2.) Of course, they cross the pn junction - if the energy is high enough (think of inertia effects). This is the case, normally, for voltages above (o,5...0.6)volts.

4.) The diode can maintain its voltage only if there is another part which can share the voltage with the diode. Normally, this is a resistor in series with the diode.
(Supply voltages rises, current rises, zener voltage nearly constant, voltage drop across the resistor rises).

Does this help?
 

LvW,your reply was certainly helpful,but before I end the topic,I need to clarify a point in regard to your answer to the fourth question....

The diode can maintain its voltage only if there is another part which can share the voltage with the diode. Normally, this is a resistor in series with the diode.
(Supply voltages rises, current rises, zener voltage nearly constant, voltage drop across the resistor rises).

On the V-I characteristics,the current beyond the breakdown voltage increases almost infinitely,while the voltage doesn't vary at all....is it true that in order to observe this,we need an additional resistor attached in series with the zener (as you mentioned)?
I thought the voltage regulation thing is an intrinsic property of the diode.
[/quote]
 

Urmi said:
..............................
On the V-I characteristics,the current beyond the breakdown voltage increases almost infinitely,while the voltage doesn't vary at all....is it true that in order to observe this,we need an additional resistor attached in series with the zener (as you mentioned)?
I thought the voltage regulation thing is an intrinsic property of the diode.
[/quote]

Your assumption "the voltage does not vary at all" is incorrect.
Of course, it does vary - however only marginal due to the dynamic resistance which is in the order of some ohms (maximum). You are not allowed to connect a Z-diode directly with a voltage source. It will be destroyed if the voltage is larger than the breakdown of the diode. Thus, you always must use a resistor in front of the diode.
The current through the resistor-diode combination varies according to the supply variation and - as a result - the voltage across the resistor varies and the drop across the diode is (nearly) constant.
There is no "intrinsic regulation property " of the diode. It has a very low dynamic resistance - that's all!
 

    Urmi

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Thanks for the clarification, LvW!!
I guess your answer also explains the 3rd question,because I was thinking that beyond the breakdown voltage,the host semiconductors' atoms all have their covalent bonds broken down in the zener diode ,but from your post I infer that that tdoes not happen.

Thanks for helping!!
 

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