Simon Dyer wrote:
I very much like the circuit by Israel Schleicher in EDN Jun 12 2003
for its ability to drive a 3.6 volt Superbright LED off a 1.2 to 1.5
volt cell with very minimal and inexpensive components. Since it
pulses the LED, greater perceived brightness can be acheived at great
efficiency. See

http://www.reed-electronics.com/ednm...e=6%2F12%2F200
3&spacedesc=designideas

According to the formula, changes to R, L or C could thoretically
provide more current to the bright white LED - I am looking for 30ma
average, but in practice I have not been able to acheive this.

Can anyone tell me where I am going wrong? I would be happy to use
three cells if it helped.

Simon,
if the LED current should be 30mA average, then it has to be with 20% duty
cycle(which is varying with battery voltage) 150mA. For this kind of current
the right transistor should be something like a BC337 with more current gain
at high currents. The inductor probably needs to be of bigger size and less
inductivity too and you can try to solve the equation given, which IMHO is
too simplified. The best would be to simulate the circuit with the free
LT-spice.
I think the first article gives a better circuit, in the pdf the connections
to the driver transistor are not drawn or got lost in some pdf-conversion,
but it is clear where they go.
--
ciao Ban
Bordighera, Italy