zxsc100 LED driver outdated?

[zachtheterrible]

I'm still having major trouble trying to get my zxsc100 DC-DC converter for my 1W flashlight working. I went to zetex's website to see if they had anything to say and of course there aren't any helpful suggestions. But as I was browsing I happened upon these DC-DC converters: **broken link removed**

I can't find the zxsc100 (the LED driver that I'm trying to get to work) on here so I'm guessing that it has been outdated. Take a look at the lighting handbook on the home page: In there you will find a 1W solution for the zxsc400. Take a look at how little the current output falls as the voltage drops. With the zxsc100, the light output of my LED drops very noticably as I lower the voltage on the board that I actually did get to work. I also like it better because of the smaller component count.

So what do you guys think? I've about had it with the zxsc100. Maybe this one will be beter.

 

[Oznog]

As far as I can tell those boost converters have 2 flaws that I'm not fond of.

One, the output is pulsed, as all boost converters will be unless an output inductor is brought in. There's a cap there to try to filter the output but these aren't very effective with LEDs with a low dynamic resistance; unless the cap is very large a small amount of voltage ripple makes the LED current vary a great deal.

Two- and this is what I think the primary problem is- I don't think they compensate for pulse width. If the battery is fully charged the output may be on for 80% duty cycle and if it's running down the duty cycle may be 40%. So even if the inductor is large and has virtually constant current, the average current the load sees is inductor current * duty cycle, so it is down by 50% when the battery runs down in this example.

I wonder if anybody makes a part that uses a ramp generator to compensate for the inductor current? So the vref it compares the shunt voltage with increases while the inductor remains in the charge phase?

 

[zachtheterrible]

Actually the output voltage is very clean, a constant 3.3v. Of course I can see the ripples if I put my scope on a more sensitive setting but it seem good enough.

As for your second flaw, I'm not sure I totally understand you. I didn't know that there is any kind of PWM. Doesn't this just charge up the inductor and once the inductor discharges it does it again?