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Photovoltaic Mosfet Driver?

Discussion in 'Electronic Design' started by Hammy, Jan 3, 2008.

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  1. Hammy

    Hammy Guest

    Is there anyway (short of the obvious a $500 to $5k high Z
    differential probe) to measure the rise and fall times of the FET's?
    The cct is here.

    I'm just testing this out on LVAC supply, but I plan on using this to
    remotely turn on-off a 10W flyback.

    The photovoltaic driver I'm using is the LH1262.

    Also is it practical to pulse the LED to say 100mA to improve the
    current drive capability. They don't show any curves for power
    dissipation vs. temp in the data sheet. If anyone has any experience
    with these some advice would be appreciated. I only have three to
    tinker with:)

    I'm using the second cell to drive a small logic level FET (5nC gate
    charge) to discharge the main FET's. I tested this on a DC supply and
    I get the full open CCT voltage Vgs=12V.
  2. MooseFET

    MooseFET Guest

    You could characterize the FETs before you put them in the circuit and
    then look at the current rise time with them in the circuit.

    Yiu can pulse the current higher at the start. You have to watch the
    temperature rise of the active area of the LED. This most likely has
    a thermal time constant of many microseconds.

    You can use a pulse generator and a resistor to try to find this time
    constant. Set the offset voltage of the generator so that the current
    about 1mA with the generator is low and watch the variation in forward
    drop just after the full current stops.
  3. 2 channel add and Invert?

  4. Hammy

    Hammy Guest

    Thanks but a probe (particularily 2) even in ten times measuring such
    a high output Z circuit would be inaccurate.
  5. Hammy

    Hammy Guest

    Thanks I'll try that.

    Would a high Z JFET instrumentation amp give me an accuarate
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