Chuck sent me the updated version for an NEC a week ago. I don't think he'd mind if I hosted it here.
post #211 of 231
2/3/03 at 8:14am
|From what I've seen of the circuit in action, I'm guessing the 2SD613 is mostly a switch to short across the 33ohm resistor during startup and then opens up (or at least conducts less) so that all the current goes through the resistor and that's what reduces the fan voltage. I noticed that the resistor warms up after the timeout but the 2SD613 is only warm during startup (when all the current is going through IT) and then gets cooler.|
|The 613 is off at startup and the fan current is supplied through the 33 ohm pullup to 15V, this gets the fans going. Once the 613 is turned on, it's emitter voltage is regulated by the zener voltage applied to the base minus a vbe which is approximately 7.5v depending on component variation.|
|Originally posted by DHarp193
FYI, there is also a fan mod for the Electrohome Marquee line of projectors that quiets the noise considerably for all you Marquee owners out there!!!
Tim Martin knows how to do it, as well as myself and a few others if interested.