9530 MOSFET vs a 9014 MOSFET

Discussion in 'General Electronics Chat' started by Glitchmobile, May 13, 2010.

  1. Glitchmobile

    Thread Starter New Member

    May 8, 2010
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    0
    If I pass the output of a 555 chip via a resistor to the gate of a 9530 MOSFET vs the gate of a 9014 MOSFET,
    I get two different voltage signal levels at Vds, when viewed on a scope.
    Another words, the scale of the square wave is greatly diminished on the 9530 MOSFET
    vs the 9014 MOSFET.
    How come?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Did you mean an IRF9530 vs an IRF9140?

    Since you didn't post a schematic of your circuit, it'll be hard to say what's going on.
     
  3. Glitchmobile

    Thread Starter New Member

    May 8, 2010
    10
    0
    Ok, here is the schematic I am tinkering with. The signal from the chip is working well thanks to your point about the required ground at pin 1.

    Now my issue is that the 555 signal effect at the Source or Drain of the irf 9530 MOSFET
    is not as pronounced as at the Gate.
    Hence I am thinking that maybe the MOSFET choice is questionable.

    The intention is to interrupt on demand, the positive 12vdc bus supply to the injector coil.
    (If this threads topic is not in the correct section, then please move it accordingly).
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The gate (basically) acts electrically like a small capacitor.
    The injector is an 11.6 Ohm load, and you have a 30 Ohm resistor in series with it to +12v, for what reason I don't know.
    Your source voltage should not change, as it's wired to 12v.
    The drain would alternate between nearly 12v and about 4v.

    I've attached a simulation of your circuit, but I've made some changes:

    1) Simplified the wide-range PWM area.
    2) Increased R1 to 2k from 1k (less current to sink via pin 7).
    3) Connected the 10k resistor to +12v instead of ground (it's supposed to keep the MOSFET turned off in case the 555 circuit fails).
    4) Added a 330 Ohm pull-up resistor by the output of the MOSFET due to the limitations of the 555 (it's output can't get higher than about Vcc-1.3v due to the Darlington follower in the output.)

    I didn't put the "vehicle control module" in there because LTSpice does not have a switch.

    I didn't have a model of either MOSFETs that you're trying to use, but the 9Z24 isn't far off.

    I don't know why you would want to do what you seem to be attempting to do.

    At best, the engine would run terrible. At worst, your engine would suffer from fuel starvation and detonation. The ECU would attempt to compensate, keeping the injector open for longer and longer periods of time. If you monkey with the injector system, you will probably be in violation of emissions control laws.

    The only reason I can think of to monkey with the injectors and their timing would be to implement a "limp home" mode, where the cylinder is fired every other power stroke. The engine power is very significantly reduced, but such a "limp home" mode would help a great deal to keep the engine cool by simply pumping through air every other power stroke.

    Cadillac's Northstar V8 engine has such a "limp home" mode; and their old "4-6-8" engine had a similar mechanism that was aimed at better fuel economy while cruising and cooler engine temps.
     
    Last edited: May 14, 2010
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