SSTC
Solid state Tesla coil
Solid state Tesla coil
An SSTC tunes one thing, the secondary, and hangs a few untuned primary turns off a bridge that drives them directly. Nothing in it stores a bang, so the arc is fed for exactly as long as the gate signal lasts, which is what makes the drive itself the design. Run it continuously and the limit is heat. Chop it with an interrupter at a few hundred hertz and the same hardware throws a longer, brighter arc on a fraction of the duty. Modulate that interrupter with audio and the arc is the loudspeaker. So the questions that come first are what the feedback is tracking, how much of the cycle the bridge conducts, and where the heat goes.
tap any part
duty 3.60 %
Every part of the diagram answers for itself. Pick one.
Rectifier
DC bus
- start heresupplyin QCW
The bus bank: sizing the reservoir
A sagging bus eats the top of the ramp and looks exactly like a tuning problem. It is not one, and the reason to fit a doubler is not the voltage. It is the energy.
- start heresafetyin DRSSTC
What will actually kill you
Not the arc. The things on this page are at DC or mains frequency, they are inside the cabinet, and they do not announce themselves.
The bridge
- start herepower stagein DRSSTC
IGBT or MOSFET, and why SiC is not an upgrade here
One choice that sets both the frequency you can run and how long the bridge lives. And SiC is not the automatic upgrade it looks like.
- start herehow it works
What the bridge does
Four transistors arranged so they can connect the primary across the supply one way round and then the other. Everything else exists to serve it.
- power stage
Dead time and the freewheel diodes
Adding dead time to be safe makes it worse, in a loop: longer pause, more diode current, worse turn-off, harder hit at the next turn-on.
Gate drive transformer
- start herehow it works
What a gate transformer is for
The top devices have their emitters on a node that swings by hundreds of volts. You cannot wire logic to that, so the signal goes across magnetically.
- gate drive
Diagnosing a gate waveform: symptom, cause, cure
Three faults look alike on a scope and their cures are mutually exclusive. Without knowing which is which you turn the resistor and make it worse.
- gate drive
Choosing a gate resistor: the gate loop is an RLC
A gate resistor cannot be chosen apart from the transformer feeding it. Lower it while the leakage stays and what you get is ringing, not speed.
Driver
Interrupter and modulator
- start herecontrolin DRSSTC
The interrupter: bangs per second, ontime and duty
Bangs per second is the frequency of the note in hertz. There is no best rate, only a note, and two settings on this box kill transistors.
- start hereregimes
CW or pulsed: the criterion that decides the topload
The argument goes round forever because both sides are arguing about the circuit. It is not a property of the circuit, it is a question of time scale.
Current transformers
Tank capacitor
Primary
- start herehow it works
An SSTC primary is a different part
Most of what you have read about primaries does not apply here. This one is not tuned at all: it is a transformer winding trying to be a good one.
- resonator
Soft or hard switching, and why an SSTC couples tight
Whether a coil switches softly comes down to five characters. A loose primary at k = 0.15 never gets there, and the loss is five times the conduction.
Secondary
- start herewinding
Winding and measuring a secondary
Not a transformer winding that happens to be long. Almost everything that goes wrong with one goes wrong because it was wound as though turns were the point.
- failure
The second mode, and flashovers in the middle of a winding
A failure that looks like too much coupling and is not. It also explains why a two inch secondary works in a DRSSTC and burns in a bare SSTC.