Fast transistor at high current

Scarecrow

Hi Guys,

My problem is simple, i need a transistor or darlington or FET or whatever does the job to get a positive current of 1.8A 5v on and off in less than 100-300 nanoseconds =S hehe is it possible?????

Thanks a lot.....
···················· ............Javier

LoopyByteloose

BJTs are generally able to switch faster than FETs because they have less internal capacitance, but in some configurations the FETs internal capacitance is negated. Try reading 'The Art of Electronics'

The problems with BJTs are heat. With Darlingtons, you have more gain and even more heat.

I think it is possible and you may even get a FET taylored to direct input from TTL to do the job, but the device may have to be between the FET and the grounded side. This implies that you would not be able to use a voltage higher than the output of the TTL [noparse][[/noparse]I assume a Stamp] and it might drop a bit -- to 4.4volts.

FETs seem to be available for 10amps and more. They even have 'flyback' diode protection in some.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Paul Baker

IRF820, IRLD024, IRFBE20, 2SK3048 just to name a few through hole parts availible through digikey that fit your requirements (these are all N channel FETs whose Ton < 100ns)

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·1+1=10

Scarecrow

im just going to drive 32 leds that blink really fast so the voltage i need for them is 5v and heat dissipation is not a problem and i need to source the current not to sink it so isnt it a P chanel mosfet that would work for that? (sorry im just a hobbyyist trying to have some fun )

Scarecrow

the current im gonna give them is 60ma each btw and i need to blink them fast cause theyre in groups of rgb so i do that with 3 FET's in·order to make different colors·=S

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"The Only Thing Im Sure Of Is That Im Never Sure Of Anything"........

Post Edited (Scarecrow) : 1/12/2006 8:38:10 PM GMT

Paul Baker

Yes you are correct that a pchannel device is nessesary, poke around digikey to find a similar fet suitable for your application, type fet into the search box, then click on the appropriate subsection. From there limit the search by using parametric values nessesary (PMOS, current rating between -3A to 1.8A etc), click on the right most document link, look in the spec sheet for the value Ton to be sure it is less than 100ns, youll probably want a through-hole package such as TO-220 (there may be a suffix such as AB, thats fine) or DIP.

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·1+1=10

Scarecrow

ive been looking arround digikey and i saw the IRF9530 and IRF4905PBF and STP80PF55 they look quite good but i dont know if they will react as fast since im driving it with 5v..=S

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"The Only Thing Im Sure Of Is That Im Never Sure Of Anything"........

Scarecrow

o well im going to try the first one since its the easiest one for me to find...=S maybe ill post the results

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"The Only Thing Im Sure Of Is That Im Never Sure Of Anything"........

Paul Baker

Sorry, My home computer refuses to display pdfs (Adobe hangs and consumes all availible processor cycles indefinitely), Id have to be at work to verify, but you are most likely correct that it will work, just remember PMOSs are active low triggers (gate tied to ground), Ton is ussually Vgs insensitive if you are driving it well past the threshold voltage (you are).

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·1+1=10