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masoud New Member Offline Posts: 3	Power negative resistance Mar 23^rd, 2009, 7:54pm Hi everybody, Actually I am looking for a circuit of a negative resistance. I need it to work in DC and AC forms. and it should be capable to bear up to 20A (DC) for about 1sec. I will appreciate if anybody can help me. Thanks a lot, Masoud
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: Power negative resistance Reply #1 - Mar 23^rd, 2009, 8:53pm i think this -ve resistance is a small signal quantity,for 20A i am not sure whether it will come or not.Actually why u want such a high current rating -ve R? regards, Rajasekhar.
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masoud

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Re: Power negative resistance
Reply #2 - Mar 23^rd, 2009, 8:58pm

It can be done using opamp but it is not suitable for such a current so it should be done using the power transistors but I can not find proper topology because most of the transistor based topologies have -ve R in small signal and in the most cases the input current is going through the Base pin which can not bear 20A even for couple of miliseconds.
What is your idea?
It is good if I can do that for only 40-60 miliseconds for DC current

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buddypoor Community Fellow Offline Posts: 529 Bremen, Germany	Re: Power negative resistance Reply #3 - Mar 24^th, 2009, 12:50am APEX sells power opamps with output currents up to 30 A. I see no reason why the classical NIC should�t work at such high currents. It�s not only a small signal device. Try a simulation with one of APEX opamps.
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raja.cedt

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Re: Power negative resistance
Reply #4 - Mar 24^th, 2009, 1:30am

hi buddy poor,
i have question based on the your reply,even for ordinary NIC,-ve property is narrow in property i mean to say that over a small voltage range only its possible.Then how its possible for very high current,because with this high current range transistors are good only for switch purpose's rather in linear region.correct me if am wrong.
Thanks,
rajasekhar.

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masoud

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Re: Power negative resistance
Reply #5 - Mar 24^th, 2009, 10:19am

Hi Raja,
The thing you said is the main problem, ordinary transistor based -ve R are only working in small signals and I want to know if there is any topology which can produce -ve R using transistors to have -ve R even in DC mode. DC is more important than AC condition for me I mean I want a -ve R which works in DC and 20A current.

@buddy poor: thanks a lot for introducing that OpAmp it is a very good one which i didn't know thanks a lot.

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raja.cedt

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Re: Power negative resistance
Reply #6 - Mar 24^th, 2009, 9:22pm

hi,
i really surprised about -ve R at dc,can u please tell me about the application where you want to use this, because if u you are using an non inverting amplifier with +ve feedback it may possible(provided op amp has zero common mode voltage at the input),any how i don't know much..may be with your we can figure out ...

Thanks,
Rajasekhar.

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