When a high voltage power supply drives a spark load, four problems arrive at one terminal at once: the supply must survive the transient, the external circuit must limit spark-loop current and stored energy, the layout must avoid stray discharge paths, and the operator must be protected from the energy left behind. This application note treats high-voltage spark protection as a topology choice and gives each part one clear job.
The most common modeling error is assuming the capacitor rests at full supply voltage. With a passive gap it does not: it charges, self-fires at the breakdown voltage Vbd (air breaks down near 3 kV/mm, so a 1 mm gap fires around 3 kV), then collapses toward an arc-retaining floor of about 100 V. The result is a sawtooth waveform, so per-spark energy is E = ½ C (Vbd² − Vmin²) — not ½ C VHV². A series resistor large enough to starve the arc is what makes the sparking repetitive instead of a sustained discharge.
Any external load capacitor needs its own bleeder; the supply’s slow internal self-bleed cannot drain a capacitor isolated by the series resistor. Before contact: shut down, wait the bleeder interval, measure the terminal below the approved threshold with a rated probe, apply lockout/tagout, and ground the output with a chicken stick. A timer alone never proves safety — the measurement is mandatory.
Worked values are first-order design aids for ATI 5 kV models. Confirm internal capacitance, gap breakdown, component ratings, and the safe-access procedure on the assembled hardware before release.
Related ATI products: High Voltage Power Supplies · HVPS Quick Selection Guide
