Drivers circuit in combination with function generators

Discussion in 'General Electronics Chat' started by Tree1, Jun 5, 2011.

  1. Tree1

    Thread Starter Member

    Nov 30, 2010
    Sometimes people build circuits to drive devices and the input to those driver circuits is a signal from a function generator for example ,a pulse and what comes out is another pulse to that device. Why a function generator and a driver circuit just to generator a pulse ? For example, an ignition coil...

  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    There may be a question in there, but I can't quite make it out - can you rephrase that?

    By the way, discussion of automotive subjects and very high voltage projects are not allowed here, so you would be be advised to keep your enquiry general. Mentioning spark coils is liable to get your thread closed.
    Tree1 likes this.
  3. #12


    Nov 30, 2010
    A function generator generates pulses, but it doesn't provide high current or high voltage. You attach a driver circuit to provide voltage and current for the end device. For instance, 8 D batteries will provide 12 volts, but you can't get 400 amps out of D batteries to start a car. The function generator and driver is the same principle, only smaller.

    Is this an answer to your question?
    Tree1 likes this.
  4. Jaguarjoe

    Active Member

    Apr 7, 2010
    In an inductive ignition system, the 'coil' primary has a very low resistance, ~1Ω. It requires lots of current to charge, maybe as much as 7 amps or more. A bare function generator can't provide anywhere near that current so you'll need a driver.

    On the flip side, when the 'coil' primary circuit is opened up, a very short high voltage pulse is generated in the primary due to the coil's attempt to maintain that 7 amp current flow. The driver is designed to handle that too.

    IIRC, the Motorola MC3334 IC was an ignition coil driver that was the heart of the GM HEI system found in many millions of 80's and 90's GM cars and trucks. You can find '4 pin HEI modules' in junk yards for pennies, or buy them new for ~15 dollars. It can be easily driven by even the most feeble of generators. You can experiment and see exactly how they work.
    Tree1 likes this.
  5. Tree1

    Thread Starter Member

    Nov 30, 2010
    Thanks guys, you answered my question, I deeply appreciate that.

    Adjuster,I was not trying to encourage high voltage projects or engage in one, was just curious. Also, I am new in the world of electronics and I am just trying understand the logic of many things that I read.