Re: lm317 as current regulator


"James Thompson" <Jamesthompson2002@xxxxxxxxxxx> wrote in message
news:c9335$449e15fd$438c821c$19826@xxxxxxxxxxxxx
When using the lm317t voltage regulator with a 1.2 ohm 5 watt resistor for
1 amp limiting, my question is: Is the input limit on the ic still
limited to about 40 volts?
What I am doing is, I have a supply voltage of 60 volt dc and I want to
limit the current draw to 1 amp for an led board I made. the leds will be
a series link of 12 with 40 of these in parallel. By limiting the current
available to this panel, it should put the voltage of each led at 3.33
volt. White leds here.
Would the lm317t work in current reg mode since it will only see 20 volt
across it.
Or should I first pre-regulate the 60 volt down to say about 42 volt?


Update: Advice taken from replies.
Pcb revised to 17 led per string, with a 20 ohm .5 watt resistor per string.
At 3.5 volt per led fv drop that is 59.5 volt drop per led string, with the
remaining .5 volt on the 20 ohm resistor which sets the Current per string
to 25ma and therefore has the resistor dissipating .0125 watt. The resistor
being .5 watt will not even get warm. All power from the supply of 60 volt
is used for producing light instead of just heat. If this is correct, I
will not even need a regulator. Total Current draw for the led's will be
1.25 amp.
Does this seem to be the best configuration?


.

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