Some ignition coils with built-in transistors require a ground signal to fire. Could someone further explain? Does that mean a ground signal must be fed into the transistor's base so that it turns on and allows current through the primary winding? What really is the difference between a negativetly triggered coil and a positive triggered coil ?

Thanks!

 

The coil primary is an inductor. It soaks up current through a transistor to ground. At the proper time, the transistor turns off. Being an inductor, it maintains current flowing through it as long as it can . As the magnetic field collapses it generates a high voltage in the secondary to make the spark.
Search for an MC3334. It shows how a typical inductive ignition system works. It is the GM HEI which is in millions of '70's and '80's cars.

The spark occurs when the transistor opens up.
The transistor is only on for a period called coil dwell time, just prior to shut off.
Because we live in an NPN world, most things are referenced to ground and voltages are positive WRT ground. It would be hard for a negative grounded car to create a negative voltage.

 

Thank a million