Super Regulator, Need sub for P309 LED

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Sze

Member
2004-07-08 3:31 am
Calgary
Hello,

I want to build a few improved Super regulators as per Walt Jung's AE article. Problem is the P309 LED is no longer available from Digikey. Does anyone have any ideas as to where I can get some? Or offer an alternative LED as a substitute. Any help would be appreciated.

Thanks.
 
I use ALW's schematic as a reference:

Uled = voltage across the LED (1.6V red, 1.8V green, 3 V blue, value may vary)

Vbe = 0.7 V voltage between base and emitter

R1, prefered current 10-25 mA, I'll take 10 mA as an example.

R1 = (Uled-Ube)/I = (1.6-0.7)/0.01 = 90 ohms Red LED

R1 = (Uled-Ube)/I = (3.0-0.7)/0.01 = 240 ohms Blue LED


You must also change the voltage of the preregulator. Higher voltage of the LED => more voltage across the Q1.

Needed voltage is 0.8 + Uled (roughly) = 4-5 volts for blue LED

Preregulator
R2 = 1 k
R3 = 2.7k => 4.6 volts across Q1, collector-emitter.

As you may notice it's good to have a low voltage as reference, your losses will be less if you use a preregulator. OK, the coolness factor will be higher with a blue LED but with the sacriface of higher losses.
 
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