Joe,
The basic MSD circuit was posted on page 3 of this thread and from memory is more or less correct compared to the circuit I traced some years ago from my MSD6A. Notice a couple of things that are different than a typical inverter type power supply used in most battery powered CDIs. First, note that there are two power transistors in parallel configuration with the emitters and collectors tied together. The emitters are both connected to the same winding, not separate windings as in a typical push-pull type oscillator. Now I know that a single transistor or even two transistors in parallel can be made into an oscillator type supply pulsing a single winding, but why then would the two transistors be configured the way they are as that would require a larger transformer to handle the power which then reduces the frequency? If using two transistors why not take advantage of that to increase the frequency of the oscillation. The answer here is that the power supply is not an oscillator. The biggest piece of evidence other than testing and scope images, is that both paralleled transistors have their bases tied to the same side of the feedback winding, but more crucially, the feedback winding (which is really a feedback and control winding in this circuit) is in turn controlled by the trigger circuit (VTRIG on the schematic). The squeaking one hears from the old MSD6 spark directly mimics the power supply squeak which is not from a free running oscillator, but from the distinct sound that several short duration CD sparks make separated by 1mS. I have measured up to 5 sparks in the series at low rpm. It sounds like a squeak because the frequency is very low, IE spark rate X extra sparks at low to medium rpm.
And here's the clincher: Note that both transistors are permanently connected between the battery terminals. The emitters through the main winding of the transformer, and the collectors directly to ground. In a free running oscillator of the type more commonly used in CDIs and many other power supplies, that configuration would result in a power supply that never turned off. This one does, because the bases of the transistors are controlled directly by the trigger circuit.There is no other switch in the power supply to turn it off. Fred
joe 90 wrote: ↑Wed Feb 07, 2018 4:09 pm
Circlotron wrote: ↑Mon Feb 05, 2018 8:21 pm
joe 90 wrote: ↑Mon Feb 05, 2018 6:50 pmThe oscillator runs in the KHz frequencies
First false claim or misunderstanding.
The MSD inverter charges the cap in one single pulse in a similar principle to an inductive ignition discharging into a spark gap.
Yes it's 400Hz with an 8 cylinder and 200Hz with a 4 cylinder.
Next........waiting for someone to provide the mathematics to back up the ....."charges the cap in one half cycle"........because it can't.
Not unless the pulse transformer is the same size as an inductive ignition coil , which it isn't.
If it was........then you may as well just use inductive ignition because it's better.