5V LED ( was Re: Gecko current set resistor

Modern LED's are designed to use the 20mA and 5V as the basis for
determining resistors.

There are some different styles like ones with internal resistors and
ones with much lower power. The Garden variety is 5v-20mA

I assume you are referring to the 1.7 volt drop across the LED so
I=5/R
but 5-1.7=3.3 volts for power
so I=3.3/R or 20mA=3.3/R
In many circuits you worry abourt wasting power, but my premise is
that at 1 amp, you are not worried about an 0.02 drain.

You can power one with 40mA or lots more if you pulse the voltage,
makes it REALLY bright. if you don't get the pulse correct, it makes
it's life REALLY short. The reasoning is that amps will heat the
LED if left on too long. and if the pulses are faster than your eye
can seperate the pulses it will appear REALLY bright. and with
cooling between pulses, you do not risk the LED by over heating.

And you are correct that 5v-20mA will yield a bright light. One
question is how big is that Cap and how long will it take to bleed it
down ? and how bright will the LED be when there is still enough
charge to make you jump ?

An LED will light quite nicely at lower voltages, so as the cap
discharges you will see a dimming as the voltage reduces. At some
point you will need to be in a very dark room to see the faint glow.

An LED should work up to about 40mA, but any spikes will soon destroy
it. Also, you should have a faint glow at about 1mA. but you do
need about 1.7 volts to light it (1.9 for orange)

At what voltage will your cap still shock you ?

if you light at 20mA at 80 volts, your LED will glow dim down to very
low voltages and will blead faster than a higher resistor.

My use is not to just indicate, but to blead down the cap and read
voltages all the way to the almost safe level.

besides it LOOKs like your machine has a lot of power when it is
glowing brightly. power ummmm......


Dave

--- In CAD_CAM_EDM_DRO@y..., JanRwl@A... wrote:
> In a message dated 21-May-02 12:11:17 Central Daylight Time,
> davemucha@j... writes:
>
>
> > Figure 20mA for the current and 5V for the LED
> >
> >
> >
>
> 5 VDC is WAY too much for LED's (except those special ones with VR
> "on-chip")!!!
>
> 20 mA is BRIGHT for a T1-3/4. "Modern" LED's work fine on 10 or 15
mA!!!!!
>
>
> [Non-text portions of this message have been removed]