1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

zxsc100 LED driver outdated?

Discussion in 'General Electronics Chat' started by zachtheterrible, Oct 20, 2005.

  1. zachtheterrible

    zachtheterrible Active Member

    Joined:
    May 4, 2004
    Messages:
    2,154
    Likes:
    2
    Location:
    California, USA
    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: http://www.zetex.com/3.0/a1-7b.asp

    I can't find the zxsc100 (the LED driver that I'm trying to get to work) on here so I'm guessing that it has been outdated.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.
     
  2. Oznog

    Oznog Active Member

    Joined:
    Apr 21, 2004
    Messages:
    2,879
    Likes:
    11
    Location:
    Austin, Tx
    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?
     
  3. zachtheterrible

    zachtheterrible Active Member

    Joined:
    May 4, 2004
    Messages:
    2,154
    Likes:
    2
    Location:
    California, USA
    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?
     

Share This Page