Electronic HID ballast mod. problem

Discussion in 'General Electronics Chat' started by Morepower!, Jan 10, 2009.

  1. Morepower!

    Thread Starter New Member

    Jan 10, 2009
    I wasn't quite sure where to post this, Mods please feel free to move this if need be.

    I'm not sure what I want to do is even possible, so I thought I'd put it to the experts here. I've been increasing the output power of an existing ballast but havn't been able to get the amount of power I'm looking for before it fails.

    The problem I'm facing is having to drive the smaller components(IC's, smaller FETS, etc.) too hard, to the point where they are failing, to get the required power out from the power FETS. Basically there is a pot that seems to control the current(?) to the IC that creates the source signal(400-600Hz, square wave) then goes through a series of FETS for amplification(?). To get more output power I have simply been turning up the pot. STD output power is ~50W @ 85V, by heatsinking the power FETS properly and jumping the resistor after the pot I have been able to get ~100W @ 104V but, as I said earlier, the components under the power FETS are burning out.

    So my question is, is it possible to replace just the power FETS with others that will output the same amount of power with less input signal power ? If so what values of the replacement FETS should I be looking at ? Rdson values ?

    I'm sure it is already apparent my understanding of how this circuit and FETS work is basic at best and more than likely incorrect on many points. But hopefully I know enough to accomplish my goal.

    Many thanks
  2. nanovate

    Distinguished Member

    May 7, 2007
    Could you post a schematic?
  3. Morepower!

    Thread Starter New Member

    Jan 10, 2009
    Unfortunately being an existing, store bought product I don't have a schematic, the only thing I have is the data sheets on the power FETS(Q1 & Q3), sorry.
  4. duffy

    Active Member

    Dec 29, 2008

    Naw, man - pot is what you GROW under the HID lamps!