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RSS >  50 mA Constant Current Source, For 9 to 12 VDC Power Packs
dewey1 #1 13/09/2010 - 20h24

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Here is a schematic I generated for those wanting to use 9 to 12 VDC power packs.

This circuit will provide a constant current of 50 mA for leds that are from 1.2 to 2.0 forward volts.

This solves any dimming of leds as in battery powered devices.
Any questions just ask.
Posted Image

Here is a spec sheet if interested.
http://www.datasheetcatalog.org/datasheet2/1/03cgthpfat4t4ly5kfp5lpwladfy.pdf
Edited by dewey1 on 14/12/2010 at 20h35.
nadrealista #2 16/09/2010 - 19h08

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Hi Dewey1,

if Vref is 1.25V shouldn't these LEDs be in paralel and then R1 down to 8 Ohm?

Sorry if I missed something.

BR
dewey1 #3 16/09/2010 - 21h18

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nadrealista @ 16/09/2010 - 21h08 a dit:

Hi Dewey1,

if Vref is 1.25V shouldn't these LEDs be in paralel and then R1 down to 8 Ohm?

Sorry if I missed something.

BR



The schematic is a current limiter not a voltage regulator.

Click on the data sheet link I provided.
It gives a very good description of applications.

Vref has to do with the 317T it self.

Look on page 17 on bottom. Precision Current Limiter
Edited by dewey1 on 16/09/2010 at 22h09.
nadrealista #4 17/09/2010 - 17h37

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I see it now. Thanks for pointing out :)
dewey1 #5 17/09/2010 - 19h58

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The LM317T is a very versatile regulator.
I have used it in many designs for the last 30 years.
If you have access to one, try the circuit out!
Radio Shack use to have them. I prefer Digi-Key.
tracker #6 09/10/2010 - 19h02

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I have just LM317T and 20 ohm resistor and works great (60mA) and works from 6V. Output is 4,3V with three SFH485 diodes in serial. I mounted small heatsink because it is hot after a while.

Edit: I found out that my dc adaptor gives 8V. 6V is not enough.
Edited by tracker on 04/11/2010 at 18h32.
dewey1 #7 22/10/2010 - 13h45

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tracker @ 09/10/2010 - 21h02 a dit:

I have just LM317T and 20 ohm resistor and works great (60mA) and works from 6V. Output is 4,3V with three SFH485 diodes in serial. I mounted small heatsink because it is hot after a while.



Glad to see some one make use of this design. I am surprised that more people have not tried it.

The heat sink is dependent on current draw and the voltage differential between input and output.  Example: a 9 volt verses 6 volt supply will require more power dissipation if the current is the same.
tracker #8 24/10/2010 - 18h05

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Yes. I discovered that on 8V it's not very hot.
Edited by tracker on 04/11/2010 at 18h32.

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