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'] Constant current diodes or FETs?'
2004\06\25@161725 by John N. Power

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> From:         Harold Hallikainen[SMTP:spam_OUTharoldTakeThisOuTspamHALLIKAINEN.COM]
> Sent:         Thursday, June 24, 2004 4:37 PM
> To:   .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject:      [EE:] Constant current diodes or FETs?

> I'm loooking for a two terminal constant current device that could be put
> between an LED and a variable DC supply to hold the LED current at 5mA as
> the supply varies over a 0-10V range (recognizing we're not going to get
> it at 0V, but I'd like the widest range possible). So far i've found the
> Central Semiconductor CCLM5750 which is a nominal 5.750mA, but it takes
> 4.5V to get 80% of the rated current. Anyone have other ideas?

> THANKS!

> Harold

Constant current diodes are JFETS with their gate connected to their source.
The current rating is the same as Idso (the drain current with zero gate-to-
source voltage). This number and the maximum voltage rating are two of the
most common specs for a JFET. The third most familiar spec is the resistance
between source and drain with zero gate voltage. Knowing this and and Idso,
you can estimate the minimum forward drop. Now find a list of JFET specs
and start looking.

John Power

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