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DRSSTC: Dual resonant solid state Tesla coil

Dual resonant solid state Tesla coil

articles

Dual resonant solid state Tesla coil

A DRSSTC tunes the primary as well as the secondary and drives it in bursts, so the current in the tank is measured in hundreds of amps while the average power stays modest. That is why timing matters so much: a switch that opens in the wrong part of the cycle turns the whole design into a heater.

tap any part

220 V ACRECTIFIERDC BUSFULLBRIDGEPRIMARYMMCCT PHASECT OCDSECONDARYTOPLOADBREAKOUTGDTDRIVER + LEADINTERRUPTERFEEDBACKOVERCURRENT
bridge

Pick a part of the diagram to read what it does.

Where the power comes in, what is made of it on the way, and what tells the bridge when to fire. Every part of it answers for itself: pick one.

DC bus

  1. start heresafety

    Tesla coil safety: what in a DRSSTC will actually kill you

    The arc is not what usually kills people. The dangerous parts are at DC or mains frequency, inside the cabinet, and give no warning.

    9 min readsafety, bleeder, grounding
  2. start heresupply

    DRSSTC DC bus capacitors: loop inductance, ripple and voltage

    Working out the bus capacitance is simple arithmetic. What actually kills a bank is the wiring loop it sits in and the voltage it really sees.

    35 min readbus, capacitors, rectifier

The bridge

  1. start herepower stage

    DRSSTC IGBT vs MOSFET vs SiC: what each switch costs

    The choice of switch sets both the frequency you can run and how long the bridge lasts. Three families of parts, and the trade-offs each one brings.

    18 min readIGBT, MOSFET, SiC
  2. power stage

    DRSSTC half bridge or full bridge: layout, paralleling, what kills it

    Bridges rarely die from peak temperature. Repeated temperature swings fatigue the bond wires over thousands of cycles, well inside the datasheet limits.

    21 min readbridge, IGBT, layout
  3. timing

    DRSSTC ZCS vs ZVS, and whether a snubber helps or costs

    Switching off exactly at the current zero sounds ideal but is not. A little residual current is needed to swing the bridge node, and switching late kills parts while switching early only adds heat.

    22 min readZVS, ZCS, dead time
  4. power stage

    DRSSTC IGBT voltage overshoot: the margin is in the loop, not the bus

    The bus voltage is not what stresses the switches. They see the bus plus the overshoot from the wiring around them, and that overshoot is usually measured at thirty volts instead of at full bus.

    27 min readbridge, margin, snubber
  5. power stage

    DRSSTC IGBT pulse current rating: what the datasheet number means

    An IGBT's pulse current rating is really a statement about junction temperature, with the temperature left out. How hot you let the junction get is your decision.

    20 min readbridge, thermal, datasheet

Gate drive transformer

  1. start herehow it worksin SSTC

    SSTC gate drive transformer design: how to wind a GDT

    The top switches in a bridge have their emitters on a node that swings by hundreds of volts. Logic cannot be wired to that directly, so the gate signal crosses a transformer.

    40 min readGDT, gate drive, basics

Driver

  1. start herehow it works

    DRSSTC driver guide: what the driver board does

    The driver board does four jobs. Without it the power stage is just parts, and the frequency it has to follow is not one you can set once and leave.

    11 min readdriver, feedback, basics
  2. driver design

    DRSSTC phase lead: what it is made of, which inductor to fit

    By the time a driver sees the current zero and switches, it is already late. Phase lead makes up for that delay. What the lead network is made of, which inductor sets it, and why the usual worries about that inductor do not hold up.

    22 min readZVS, phase lead, inductor, DRSSTC
  3. driver

    DRSSTC universal driver boards, UD1.3 to UD3: which one you have

    The logic core stayed the same from UD2.1 to UD2.7, so most modifications carry across revisions. The part designators changed, and that is what trips up repairs.

    19 min readUD2, UD3, driver, history

Interrupter and modulator

  1. start herecontrol

    Tesla coil interrupter for a DRSSTC: BPS, ontime and duty cycle

    The bang rate in hertz is the pitch of the note you hear. There is no best rate, but two of the interrupter's settings can kill the transistors.

    12 min readinterrupter, MIDI, fibre
  2. safety

    DRSSTC fiber optic link to the interrupter, and the fail-safe rule

    A broken fibre must switch the coil off, and the receiver does not do that on its own. Its output in the dark is defined, and on the reference board that state means on.

    9 min readfibre, fail-safe, interrupter

Current transformers

  1. start herehow it works

    DRSSTC current transformer: what it is and what it senses

    A ferrite ring around one of the primary conductors. It is how the driver measures what the tank is doing, and it is the only sensor the machine has.

    9 min readcurrent transformer, feedback, basics
  2. protection

    DRSSTC overcurrent detection (OCD): pulse skip and why it fails

    Nothing in a DRSSTC limits the primary current except the driver's trip. Test the threshold it actually trips at, not the knob position, and start low.

    16 min readOCD, pulse skip, protection
  3. tuning

    DRSSTC tuning with a scope: reading the primary current waveform

    The primary current envelope over a whole bang is the main tuning evidence a loaded QCW gives you. It shows the pole and the runaway clearly, but not how far to move the tap.

    10 min readtuning, diagnosis, current
  4. instruments

    DRSSTC oscilloscope measurements without killing the scope

    More test equipment dies on the bench than in the arc. Keep the scope earthed and put the isolation on the circuit under test, never float the scope.

    12 min readsafety, probes, measurement

Tank capacitor

  1. tank

    DRSSTC MMC capacitor bank: sized by current, not capacitance

    The capacitance sets the resonance and is quick to work out. The number of capacitors is set by ripple current, and choosing larger parts to be safe can leave you with a bank that carries less.

    14 min readmmc, ripple, datasheet

Primary

  1. start herehow it works

    Tesla coil primary coil: what it is for in a DRSSTC

    The primary is a few turns of heavy copper with no direct connection to the secondary. What it does and why it is built that way.

    10 min readprimary, coupling, basics
  2. tank design

    DRSSTC coupling coefficient: how high to go, and what raising it buys

    Tighter coupling looks like the obvious way to a longer arc, yet the longest published coils run some of the loosest coupling.

    25 min readcoupling, racing sparks, DRSSTC
  3. tank

    DRSSTC primary circuit design: impedance, turns and detuning

    You do not set the primary current directly. It follows from the bus voltage and the impedance of the tank, and the impedance is what you actually choose.

    20 min readprimary, coupling, tuning
  4. tuning

    DRSSTC tuning: upper or lower pole, and which one the driver locks to

    Once the primary and secondary are coupled, the single resonance splits into two. The secondary frequency you measured on its own is no longer one the coil runs at.

    43 min readpoles, tuning, PLL

Secondary

  1. start herewindingin SSTC

    SSTC secondary coil design: how to wind and measure it

    The secondary is a resonator, not just a long transformer winding. Most secondary problems come from winding it as if the turn count were what mattered.

    23 min readsecondary, racing sparks, grounding
  2. failure

    Tesla coil ground strike: what one does to a DRSSTC

    A ground strike has five separate effects on the machine. The mild strike is the one that can push the driver onto the wrong mode.

    17 min readstrike, poles, feedback
  3. resonator

    Magnifier Tesla coil: why a DRSSTC magnifier is not a longer coil

    A magnifier has three coils and two couplings, and the case for it rests on the coupling the driver can hold. In the one published comparison with numbers, it made less spark per inch of winding than the same builder's two-coil machine.

    23 min readmagnifier, coupling, resonator

Topload

  1. start hereresonatorin SSTC

    SSTC Tesla coil top load: what it does, what it costs, what QCW changes

    A bigger topload costs secondary voltage, and voltage is what makes the arc long. Whether it pays off depends on how much the arc detunes your coil.

    32 min readtopload, breakout, tuning

Breakout point

  1. start herehow it works

    Tesla coil breakout point: what it is for on a DRSSTC

    A breakout point gives the discharge a place to start, which is one of the few ways to aim it. What it should be made of, and why it wears out.

    5 min readbreakout, topload, basics
  2. first run

    Tesla coil not working: DRSSTC with no sparks or short sparks

    What to check, and in what order, when a coil runs but nothing leaves the breakout. The usual causes are wiring and grounding faults, not tuning.

    14 min readdebugging, tuning, first run

The discharge

  1. start herearc physics

    DRSSTC streamers: how a Tesla coil arc grows, branches and bends

    A spark front moves at metres per microsecond and a bang lasts about three hundred microseconds, yet the arc grows about ten centimetres, not seven hundred metres. The limit is how fast charge reaches the tip.

    18 min readarc, streamer, branching

RF ground

  1. start herehow it worksin QCW

    QCW Tesla coil grounding: RF ground, counterpoise, three grounds inside

    The bottom of the secondary needs a return path, and the mains earth is not it. Outside the coil the ground is one side of the circuit; inside the driver it is three separate grounds that must not be joined.

    14 min readgrounding, counterpoise, isolation