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.
DC bus
The bridge
- start herepower stagein DRSSTC
DRSSTC switches: IGBT, MOSFET or SiC, and what each one costs
One choice that sets both the frequency you can run and how long the bridge lives. Three families, and what each of them makes you pay for elsewhere.
- power stagein DRSSTC
The DRSSTC bridge: half or full, layout, paralleling, what kills it
Peak temperature is not the mechanism. The size of the swing tears bond wires over thousands of cycles, a long way below anything on the datasheet.
- power stage
SSTC dead time: the pause, the diodes, and how much is too much
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
How to wind a GDT: the gate drive transformer in an SSTC
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 an SSTC 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 an SSTC 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
- start herecontrol
Inside an SSTC driver: feedback, phase lead and protection
The network holds a constant angle while the hardware needs a constant time. That mismatch is the limit of the whole technique, and a QCW walks straight into it.
- start herehow it worksin DRSSTC
What a DRSSTC driver does
Four jobs on one board. Without it the power section is a box of parts, and the frequency it has to find is not a number you can set once.
- control
SSTC driver start-up: every bang starts open loop
A current-feedback driver cannot start on the signal it exists to produce. The handover out of that blind state has its own settings and its own failures, and they look exactly like weak feedback.
Interrupter and modulator
- start herecontrolin DRSSTC
The DRSSTC 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
SSTC, 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
- start heresensing
SSTC current transformers: why feedback and protection need two
Taking the feedback and the protection off the same current transformer saturates its core, and the protection gets weaker exactly when it is needed.
- start herehow it worksin DRSSTC
What a DRSSTC current transformer is, and what it senses
A ferrite ring on one of the thick conductors. It is how the driver finds out what the tank is doing, and it is the only sense the machine has.
- feedback
SSTC feedback: from the primary, the secondary or an antenna
Three places to sense the resonance, and the choice is inherited from whichever schematic you copied. Each is prone to a different failure, and one mechanism sorts all three.
Tank capacitor
Primary
- start herehow it worksin DRSSTC
What a DRSSTC primary is for
A few turns of heavy copper that are not connected to the secondary anywhere, and are not trying to be.
- 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 k squared Q. A loose primary at k = 0.15 never gets there, and its switching loss is nearly five times its conduction loss.
Secondary
- start herewinding
How to wind and measure a Tesla coil secondary for an SSTC
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 SSTC second mode, and flashovers mid-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.