Press-pack (disc) thyristors and diodes: ceramic hockey-puck power semiconductors from 1,800 to 8,500 V, clamped between heat sinks, and the clamping force, contact resistance and series or parallel matching they depend on

01

Blocking voltage against current: one supplier's phase-control thyristor range from 60 mm to 192 mm housings

Hitachi Energy's phase-control thyristor (PCT) table shows how average current falls as blocking voltage rises within the same housing, and how the housing — given as maximum diameter / pole-piece diameter — grows with current. [1]

Editorial calculation: in the 150 / 100 mm housing the average current rating drops from 6,100 A at 1,800 V (5STP 50Q1800) to 2,870 A at 8,500 V (5STP 27Q8500) — about 2.1 times lower. Surge rating relative to average current also differs by part: 94.0 kA / 6,100 A ≈ 15 for the 1,800 V device, 65.0 kA / 2,880 A ≈ 23 for the 5STP 26N6500. [1]

The table lists five 1,800 V parts, six each at 2,800 V and 4,200 V, seven at 5,200 V, ten at 6,500 V, one at 7,200 V and three at 8,500 V, in housings from 60 / 34 mm to 192 / 143 mm. [1] The photograph above shows the format next to other packages: a ceramic disc with two flat pole faces, a stud-mounted device with a threaded base, and plastic-cased power modules, one of them on a finned heat sink.

State the repetitive blocking voltage, average and RMS current, surge current and its duration, cooling (single- or double-side, air or water), and the housing / pole-piece diameter your clamp and heat sink are built for.

02

Clamping force sets thermal resistance and on-state voltage: Dynex's minimum, 1.22 × minimum maximum and the ±10 % window

Dynex explains why a disc device needs its clamp: unlike a stud device, the interfaces inside the housing — copper electrodes against molybdenum discs and washers — are dry, so their contact electrical and thermal resistances add to the bulk resistance until enough pressure closes them. Its measurements on a DCR3990A52 thyristor plot junction-to-sink thermal resistance and on-state voltage (at 4,000 A, 125 °C) against clamping force. [2]

Dynex defines the minimum clamping force as the force above which thermal resistance and forward voltage no longer improve significantly, and sets the maximum at 1.22 × the minimum; devices are temperature-cycled at that higher force, and the datasheet figure is the mean ±10 %. The user has to keep the force inside those limits under all tolerances of the clamp and all thermal expansion, and spread it evenly over the whole contact area with thick, stiff buffers; uneven clamping raises thermal resistance and forward voltage and can damage the thyristor. [2] Editorial calculation: a mean of F ± 10 % spans 0.9 F to 1.1 F, and 1.1 / 0.9 ≈ 1.22, so the published window and the 1.22 ratio describe the same range; for an example mean of 100 kN, the clamp has to stay between 90 and 110 kN. [2]

Dynex also warns against clamping a fully floating device at room temperature and then heating it from outside on a hotplate or by an adjacent device: the metal parts expand more than the silicon and can put it into tension and crack it, whereas heat generated in the silicon in service keeps it in compression. [2]

Ask for the datasheet clamping force (mean and tolerance), the clamp and buffer design, the joint resistance measured at 100 A after assembly, and the interface compound used.

03

Stacking discs in series and parallel: leakage and on-state voltage bands, balancing resistors and current derating

Dynex names variation in leakage current as the main cause of unequal voltage sharing in series strings, while on-state voltage differences upset current sharing between parallel devices. Dynex measures leakage at 25 °C and at maximum junction temperature under maximum blocking voltage in routine production, ships the values with each device, and can band devices with similar leakage, marking the band ("A", "B" and so on) on the device. [3]

For steady-state voltage sharing Dynex recommends a resistor across each device, in addition to the RC snubber, when high DC voltage is applied for long periods; in a straightforward design the resistor carries two to five times the device's leakage current at operating temperature and voltage (typ.), or its value can be bounded with a formula using the number of devices, resistor and string-voltage tolerances, device voltage rating, string voltage and maximum leakage. [3] Editorial calculation, with example values only: for 3,000 V across each device and 50 mA leakage, two to five times leakage is 100–250 mA, so R = 30 kΩ to 12 kΩ, dissipating 300 to 750 W per device — which is why Dynex prefers the highest resistance that still balances the string. [3]

For parallel devices, Dynex calls for a symmetrical layout with similar conductor lengths, all devices on a shared heat sink with uniform clamping pressure, and a derating factor on maximum current that grows as more devices are paralleled; matching (banding) on-state voltage is the key parameter for parallel connection and the charge Qs for series connection. It notes that on-state voltage variation may not be reducible below 50 mV and that large orders cannot always come from one batch, so multiple bands may be needed. [3]

For a stack, state the number of devices in series or parallel, the string voltage, the required banding (leakage, Qs or on-state voltage), the balancing resistor and snubber values, and the current derating applied.

04

Disc device details to send

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Device: [thyristor or diode; V_DRM / V_RRM; I_TAV; I_TSM and duration]
Housing: [max / pole-piece diameter; single- or double-side cooled]
Clamp: [force mean and tolerance; clamp type; buffers]
Cooling: [air or water heat sink; interface compound]
Stack: [series or parallel count; banding; balancing resistors; snubber]
Acceptance: [joint resistance at 100 A; test data supplied with devices]

See manufacturer records Send an enquiry through CNFX