I Found It /ubbthreads/images/graemlins/smile.gif .. just a few seconds before...
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cgpeanut said:
Here's a Q3 runtime chart DJ made a while back.
1) The RED is unmodded Q3 with R123 and BLUE is unmodded Q3 with CR123. In any combination of Luxeon bin with TPS73201(450mA) is brighter than Q3 + CR123 and also more consistent brightness.
2) CYAN lines are p-fet burst (=DD). On low Vf Luxeon with fresh charged R123, it is much brighter than LDO, but not long, less than a minute or so.
3) The jumping up of the brightness indicates the LDO going out of constant current regulation. From this point, it just give everything. the LDO has suppressed down the current by eating up the voltage while on regulation. If regulation goes off early, we get more light. That means we are actually wasting some potential light output by burning it as heat in LDO.
Using a TPS73201 to get 450mA current, it requires 3.55V-3.7V plus 0.1V by LDO. So high Vf bin will go off regulation early and low Vf bin will go on regulation through out the time.
Here's the kicker!
For balanced runtime, regulation, output, a dual TPS73xxx is recomended for which the board was specifically made this requires two LDO chips AND provides protection to the lux. Basically, it uses the 2nd LDO to flash the lux into burst mode.
This is good, because it ensures that the current to the luxeon is controlled not going over certain limit and good for the luxeon's health. Another interesting thing is the brighter light output with higher Vf Luxeon such as SY0K brighter than TX1J. I don't know why maybe someone can explain.
To recap the point, higher Vf bin will give brighter light output as long as the Vf is still lower than nominal battery voltage.
Here's the other kicker!
For thise wanting the brightest "Burst Mode" but sacrificing the health of the lux consider a single LDO only version but higher Vf bin will have to be used for brighter light as long as it is still within the regulation voltage range.
A p-fet will be used to drive the lux into burst mode letting it absorb as much current as it can. DJ placed a timer in it so it won;t hurt the lux too much.
This can be offered with minimal customization of the pcb board. Let me know so I can make the changes. Now that we determined who get the sammie versus Q3 let's tackle this, runtime vs brightness issue.
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Hope this will help others too...
