Hello,

I noticed the following circuit in a friend design of a very cost
sensitive product and am curious what the people think about it.

The PIC (e.g. 16F73) is to drive an high voltage LED such as digikey
441-1009-ND
(http://rocky.digikey.com/WebLib/Sunbrite/Web%20Data/SSP-01TWB9WB12.pdf)
. The general idea is to drive the LED directly from the PIC, saving an
extra high voltage driver (actually, there are few LED in this circuit,
each is driven seperatly).

The circuit is as follows:


  [14V]----[A LED C]----[R1]---(A)----[R2]----[GND]

Where R1 is the current limiting resistor for the LED, point A is
connected to a PIC digital output and R2 is a relativly large resistor
(about 50K or so). The idea is that to turn the LED off, the PIC output
goes to HIGH or TRI_STATE and because of the 'knee' of the LED curve and
the resistor R2 that draws a minimal forward current, the voltage at the
PIC will not exceed its VDD.

Does this make sense ? How about if the PIC is operating on 3V only ?

Thanks,

Tal

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