Trav
Posts: 20
Joined: Mon Mar 05, 2012 10:02 pm

Re: Driving a single high power LED using PWM

Fri Jan 31, 2014 2:50 pm

Here is a possible CLD:
http://uk.mouser.com/ProductDetail/Cent ... TFjQ%3d%3d
Note CLDs are also known as Current Regulating Diodes (CRN)/
1st Batch Model B (256M) running Raspbian, Pibrow case, with RaspiCam.
Model A (256M) running Raspbmc, caseless.

Trav
Posts: 20
Joined: Mon Mar 05, 2012 10:02 pm

Re: Driving a single high power LED using PWM

Fri Jan 31, 2014 6:03 pm

Here is an updated circuit:
circuit_new.jpg
circuit_new.jpg (33.9 KiB) Viewed 1067 times
To give a range from 0.5A to about 2.0A use the following values:
CLD 3.3 mA
R1 0.2Ω at 1 Watt
R2 39Ω + 500Ω pot
R3 470 or 680Ω
TR1 & TR2 BD681

These are based on the minimum hfe of TR1, which is 750. I can't find figures for typical values. However, for hfe = 1000 the range shifts to 0.54 - 2.5 amps.
I also found that the saturated voltage of the Darlingtons is 2.5 volts (I expected less than a volt) so 5 volts won't allow the LED to light for the complete circuit, so it will need powering from 12 V, but you can probably test from 5V right up until you add TR2.
1st Batch Model B (256M) running Raspbian, Pibrow case, with RaspiCam.
Model A (256M) running Raspbmc, caseless.

mattius
Posts: 87
Joined: Thu Jun 14, 2012 9:55 am

Re: Driving a single high power LED using PWM

Sun Feb 02, 2014 5:17 pm

After playing with the Cree 1100 lumens led, i've decided its way more than required.

Im now switching down to a luxeon rebel which requires 700ma at 3.3V, i may run 2 but it should make the circuit much simpler, no?

http://www.conrad-electronic.co.uk/ce/e ... 2?ref=list

Cheers

techpaul
Posts: 1512
Joined: Sat Jul 14, 2012 6:40 pm
Location: Reading, UK
Contact: Website

Re: Driving a single high power LED using PWM

Sun Feb 02, 2014 5:29 pm

Read Table 3 of the data sheet the Vf can be anything between 2.49V and 4.05V

So unless you have a constant current source or better two. Driving two LEDs will be fun when one is at one extreme and other at opposite extreme

Also check Table 12 on Vf binning.

Also you do realise these are surface mount devices
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/

mattius
Posts: 87
Joined: Thu Jun 14, 2012 9:55 am

Re: Driving a single high power LED using PWM

Sun Feb 02, 2014 7:39 pm

anyone have any experience with other high power LEDS

Aseel
Posts: 1
Joined: Sat Feb 18, 2017 9:14 pm

Re: Driving a single high power LED using PWM

Sat Feb 18, 2017 10:12 pm

This might be redundant, but I'm a newbie and not that well with electronics.

I have a system that is consisted of:
R.Pi 3 model B (2.5 A, 5 v)
R.Pi camera v2
KD-202A-1 LED (3.7v, 1 A at full power)

I'm trying to create the circuitry to integrate the LED with the Pi system such that the entire system is powered by one 5v battery pack that should last up to 5 hours. I was told that a 2N222 transistor would do the job, but not sure what other components needed for the circuit to function properly?

Any help is appreciated! :)

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