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[TCML] OLTC midi problem
A small problem that I would like to present to more experienced
I have been building a small OLTC that is still in testing phase.
The coil produces about 2.5 feet long arcs and runs great with the basic
PWM controller I have made to give the 0-500bps.
IGBT is a 1200v 600A, and is driven by a simple 30A driver IC and
circuit, with isolated PSU, and opto coupler isolates between the driver
and the PWM control box.
PWM control box is metal, negative to case, powered by battery and
connected via a coax cable with the shield connected to mains supply
earth at the driver end.
So with this set up, the coil runs great...
I then bought a basic midi interface from EVR, and assembled, tested etc
the board and set pulse output to suit the needs of my setup. (also
running off battery...)
Connected in place of my manual controller and runs great upto about 75%
power input to the coil.
Even a fraction above the 75% mark and suddenly, nothing but the
Moved controller further away... still faults at the same 75% mark.
Scope across output of midi controller is clean and runs continuously
even when spluttering, so I ruled out the controller.
So I put scope accros the Gate of the IGBT... and what do you know, the
problem went away!
Next I removed the scope and connected the Emitter side of gate to
ground via a 1000pf capacitor (i cant ground it directly due to
circulating currents) and it also solved the problem, running upto full
power no problem...
So my question is, what was the real cause of the problem?
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