'] Constant current diodes or FETs?'
John N. Power
|> From: Harold Hallikainen[SMTP:HALLIKAINEN.COM] harold
> Sent: Thursday, June 24, 2004 4:37 PM
> To: MITVMA.MIT.EDUPICLIST
> 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?
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.
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