CONNECTING HUNDREDS OF TURNS

Tabs or extended foil?

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A metal strip touches the foil at one or two points

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Each foil sticks out one end of the roll

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Molten metal sprayed on the ends welds to every turn at once

Extended foil connects every turn in parallel, so current only has to cross the foil's width.

TABS

The long way round

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The path Current runs along the spiral to reach the tab: metres of foil only micrometres thick

Inductance A long path means more ESL, which slows a discharge

Resistance More ESR and current crowding near the tab, making hot spots

Still useful Fine for low-current parts, and simple to make

Tabs are simple, but they make the current take the scenic route.

EXTENDED FOIL

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Offset foils Foil A overhangs the left end of the roll, foil B the right

Schoopage Zinc or aluminium is arc- or flame-sprayed onto each end

Short path Current crosses a few centimetres of width instead of metres of length

Leads Wires or straps are soldered or welded onto the sprayed ends

The spray turns the ragged end of a roll into one solid terminal touching every turn.

WHY PULSE PARTS CARE

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Low inductance Pulse capacitors aim for tens of nanohenries of ESL

Peak current Spreading kiloamps over the whole edge keeps current density survivable

Low loss Less ESR means less heat per shot and a faster repetition rate

Heat path The sprayed ends act as heat-sink plates tied to every turn

Low inductance and high peak current both come from the same design choice: extended foil with end spray.

WHAT GOES WRONG

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Folded or crushed edges Poor spray contact, high ESR and local heating

Poor adhesion or porosity The contact cracks under repeated pulses and fails in life

Overspray Metal creeping past the margin can bridge the two foils

How it's caught Pull and peel tests on spray, ESR and ESL checks, and ring-down tests

Foil offset, margin width and spray quality are key yield levers on a pulse capacitor line.

UNIT 6 STUDY COMPLETE

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You've seen why extended foil and end spray give pulse capacitors their low inductance and high peak current.