The DO-9 package is a JEDEC stud-mount rectifier outline, registered today as DO-205AB. It carries hermetic silicon power diodes rated roughly 200 A to 480 A, with the common 400 A parts blocking 800 V to 1600 V. The body is a round metal can about Ø 28.5 mm (1.08 in) across, seated on a 32 mm hex base, threaded onto a 3/4-16 UNF-2A stud, with a flexible flag lead that pushes overall length near 200 mm (7.87 in). Below are the verified DO-9 dimensions, thread options, ratings, and mounting rules.
Key takeaways
- DO-9 and DO-205AB name the same outline. DO-9 is the retired JEDEC label; DO-205AB is current. A datasheet may print either.
- Two DO-9 drawings exist. The 400U outline uses a 3/4-16 UNF-2A imperial stud; the 240U outline uses an M16 × 1.5 metric stud. Confirm which one before you tap a heatsink.
- Body size: a round can up to Ø 28.5 mm (1.08 in), on a 32 mm hex base, with roughly 39 mm (1.53 in) of metal height before the lead.
- Current class: about 200 A (Vishay SD203) up to 480 A (Vishay SD400), with 400 A the volume part, at 800–2500 V depending on the device.
- Torque is capped: 27 N·m ± 10 % on unlubricated threads for the 400U family. A 3/4-inch stud tempts over-torque; the glass-to-metal seal does not forgive it.
- On the stud ladder, DO-9 sits one rung above DO-8 (~150 A, 3/8-inch stud), and it is a thinning-out package — Vishay’s 400U series reached end of life in December 2024.
What the DO-9 package is
DO-9 is JEDEC’s Diode Outline case style 9, a stud-mount (bolt-mount) case for high-power rectifiers. Construction is a hermetic metal can with a glass-to-metal seal: one terminal is the threaded metal stud at the base, the other is a heavy flexible flag lead ending in a bolt hole. Both the stud and the lead fasten to a heatsink or busbar, which is how the part sheds heat at these current levels.
The naming has two layers. JEDEC retired the DO-9 designation and re-registered the outline as DO-205AB under JEP95. Vishay’s own pages label the package “DO-9 (DO-205AB)”, and its 400 A datasheet lists the case style as DO-9 (DO-205AB) directly. A “DO-9” and a “DO-205AB” of the same current and voltage rating are the same part.
DO-9 belongs to the larger DO-205 stud family. DO-205AA is the smaller DO-8 (~150 A); DO-205AB is DO-9 (~200–480 A). The jump from DO-8 to DO-9 is a real step in iron: the stud grows from 3/8-inch to 3/4-inch, the body from Ø 23.5 mm to Ø 28.5 mm, and the current class roughly triples.
[IMAGE 1: Dimensioned outline drawing of a DO-9 / DO-205AB stud rectifier, showing stud, hex base, round body, and flexible flag lead | alt: “DO-9 package stud diode outline drawing DO-205AB”]
DO-9 outline dimensions
The table below lists the controlled dimensions from Vishay’s DO-205AB (DO-9) outline for the 400U(R) family (Doc 95339). Values are the specified maxima, minima, or nominals; consult the manufacturer drawing for the fully toleranced figure, since DO-9 ships in more than one outline variant.
| Feature | Metric | Imperial |
| Round package body diameter (max) | Ø 28.5 mm | 1.08 in |
| Hex base, across flats (wrench size) | 32 mm (SW 32) | — |
| Metal body height, excl. lead (max) | 39 mm | 1.53 in |
| Hex base height (max) | 21 mm | 0.82 in |
| Threaded stud length (max) | 16 mm | 0.63 in |
| Terminal glass-metal seal diameter (nom) | Ø 8.5 mm | 0.33 in |
| Flexible flag-lead free length (min) | 75 mm | 2.95 in |
| Overall length, stud tip to lead end | 200 ± 10 mm | 7.87 ± 0.39 in |
| Flexible lead cross-section | 35 mm² | 0.054 in² |
| Stud thread (standard / metric option) | 3/4-16 UNF-2A / M16 × 1.5 | — |
Two numbers drive the mechanical design. The body diameter of Ø 28.5 mm sets the minimum hole spacing on a busbar, and the 200 mm overall length is dominated by the flexible lead, not the can — the same detail that trips people sizing an enclosure from the body alone. Distributor “package dimensions” often quote the lead-and-body span, not the metal body.
Two DO-9 outlines: imperial stud vs metric stud
DO-9 is not a single drawing. Vishay publishes at least two DO-205AB outlines that differ mainly at the stud, and mixing them up strips threads. The 400U(R) outline (Doc 95339) specifies a 3/4-16 UNF-2A stud; the 240U(R) outline (Doc 95317) specifies an M16 × 1.5 metric stud as standard. The body and hex are close but not identical.
| Feature | 400U(R) outline (Doc 95339) | 240U(R) outline (Doc 95317) |
| Body diameter, max | Ø 28.5 mm (1.08 in) | Ø 27.9 mm (1.10 in) |
| Hex across flats | SW 32 mm | SW 32 mm |
| Hex base height, max | 21 mm (0.82 in) | 21 mm (0.82 in) |
| Standard stud thread | 3/4-16 UNF-2A | M16 × 1.5 |
| Overall length, max | 200 ± 10 mm (7.87 in) | 190 mm (7.48 in) |
| Terminal seal diameter | Ø 8.5 mm (0.33 in) nom | Ø 8.4–8.9 mm (0.33–0.35 in) |
The practical rule: 3/4-16 UNF and M16 × 1.5 are not interchangeable, and neither is a drop-in for the other in a tapped heatsink. Read the specific device’s outline document, not a generic “DO-9” reference, before you drill, tap, or order mounting hardware.
Electrical envelope of DO-9 devices
DO-9 is an outline, not a single part, so ratings depend on the die inside. Three Vishay families bracket the range:
| Device family | IF(AV) | VRRM range | Datasheet |
| Vishay SD203N/R | 200 A | 400–2500 V | Doc 93170 |
| Vishay VS-400U(R) | 400 A (TC 120 °C) | 800–1600 V | Doc 93510 |
| Vishay SD400N/R | 480 A | 1600–2400 V | Doc 93548 |
The 400 A VS-400U(R) is the reference device. Its datasheet (Doc 93510) specifies a maximum average forward current of 400 A at 120 °C case, an RMS current of 630 A, and a non-repetitive surge current of 8250 A at 50 Hz (8640 A at 60 Hz) with no voltage reapplied. The I²t for fusing is 340 kA²s at 50 Hz — the number a fuse-coordination calculation needs, and one no distributor page carries. Forward drop is 1.62 V at 1500 A peak, with a threshold voltage of 0.77–0.85 V and a slope resistance of 0.49 mΩ.
[IMAGE 2: Side-by-side of the 400U imperial-stud DO-9 and the 240U metric-stud DO-9 | alt: “DO-9 imperial 3/4-16 stud versus metric M16 stud outline”]
Mounting, torque, and thermal interface
Torque control keeps the hermetic seal intact. Vishay caps mounting torque for the 400U family at 27 N·m with a ± 10 % tolerance on unlubricated threads. That is far above the 17 N·m ceiling of the smaller DO-8, because the stud is larger — but the failure mode is identical: exceed it and you risk cracking the glass-to-metal seal and venting the package.
For heat, the 400U specifies a junction-to-case thermal resistance of 0.15 K/W (DC) and a case-to-heatsink resistance of 0.04 K/W on a smooth, flat, greased mounting surface. Mount the stud to a flat, deburred, thermal-greased seat, and clamp the flag lead to the heat path where the layout allows, because both terminals conduct heat. Approximate part weight is 250 g, heavy enough that vibration-prone assemblies must support the lead rather than leave it cantilevered.
Where DO-9 sits in the stud-diode family
DO-9 is one rung on the JEDEC stud-rectifier ladder. Current class scales with body and stud size:
| Package (old / JEDEC) | Typical IF(AV) | Standard stud | Example device |
| DO-4 / DO-203AA | ~12–25 A | 10-32 UNF | Vishay 12FL |
| DO-5 / DO-203AB | ~40–85 A | vendor-specific | Vishay 40–85HFL |
| DO-8 / DO-205AA | ~150 A | 3/8-24 UNF | Vishay VS-150U; 1N3289 |
| DO-9 / DO-205AB | ~200–480 A | 3/4-16 UNF (or M16×1.5) | Vishay VS-400U; SD203; SD400 |
Reading up the ladder, DO-9 is where a designer lands when a DO-8 at ~150 A runs out of headroom and a capsule package is not yet warranted. Above DO-9, JEDEC continues into larger DO-205 and capsule (DO-200) outlines for parts in the many-hundreds-of-amps range.
Sourcing and obsolescence
DO-9 is a mature package, and the supply picture reflects that. Vishay’s VS-400U(R) 400 A series — the volume DO-9 standard-recovery part — reached end of life in December 2024, with the manufacturer directing designers to contact them for alternatives. Other DO-9 families (SD203, SD400) remain listed, and distributors such as DigiKey and RS still stock DO-205AB parts, but the trend is downward: this is a package engineers describe as one of the smallest high-power stud outlines and one that has been thinning since the early 2000s.
For a new design, treat DO-9 as a maintenance or second-source choice, not a default. If you are replacing an obsolete DO-9 diode, match the outline variant (imperial vs metric stud), the polarity (stud cathode vs stud anode), and the voltage code before the current rating, since a mechanically identical part with the wrong stud thread or polarity will bolt in and still fail the circuit.
Frequently asked questions
What package is DO-9?
DO-9 is JEDEC Diode Outline case style 9, a stud-mount case for high-power rectifiers, registered today as DO-205AB. It houses hermetic silicon diodes rated roughly 200 A to 480 A, with a threaded stud on one end and a flexible flag lead on the other.
What is the DO-9 stud thread size?
It depends on the device family. Vishay’s 400U(R) DO-9 outline uses a 3/4-16 UNF-2A imperial stud, while the 240U(R) DO-9 outline uses an M16 × 1.5 metric stud as standard. The two are not interchangeable, so confirm the specific part’s outline drawing.
What is the mounting torque for a DO-9 diode?
For the Vishay 400 A DO-9 (400U series), maximum mounting torque is 27 N·m with a ± 10 % tolerance on unlubricated threads. Exceeding it risks cracking the glass-to-metal seal. Always torque to the specific datasheet, since values differ by device and lubrication state.
Is DO-9 the same as DO-205AB?
Yes. DO-9 is the older JEDEC name and DO-205AB is the current JEP95 registration for the same stud outline. Manufacturers often print both, as in “DO-9 (DO-205AB)”. Parts of the same rating are physically interchangeable regardless of which label appears.
How much current does a DO-9 diode handle?
DO-9 devices span roughly 200 A (Vishay SD203) to 480 A (Vishay SD400), with 400 A parts the most common. Blocking voltage ranges from about 800 V on the volume 400U parts to 2500 V on the wide-voltage SD203 family.
Are DO-9 diodes obsolete?
DO-9 is a declining package. Vishay’s 400U 400 A series reached end of life in December 2024, though other DO-9 families remain listed and distributors still stock DO-205AB parts. For new designs, plan a second source; for repairs, match the exact outline variant and polarity.
Bottom line
Choose DO-9 (DO-205AB) when you need a hermetic stud rectifier in the 200–480 A class and you are maintaining or matching existing hardware rather than starting clean. Before you order, pin down three things: the stud (3/4-16 UNF-2A or M16 × 1.5), the polarity (stud cathode for a “U” or no-suffix part, stud anode for an “R” part), and the voltage code. Torque the 3/4-inch stud to 27 N·m ± 10 % on a flat, greased seat, support the flag lead, and verify availability early — with the 400U series now end-of-life, the DO-9 you design in today may need a second source tomorrow.
[IMAGE 3: Stud-diode family size ladder from DO-4 to DO-9 with body and stud dimensions | alt: “stud diode package size comparison DO-4 DO-5 DO-8 DO-9”]
External primary sources
- Vishay VS-400U(R) product & datasheet: https://www.vishay.com/en/product/93510/
- Vishay DO-9 (DO-205AB) category: https://www.vishay.com/en/diodes/med-high-diodes/do-205ab/
- Vishay 240U(R) DO-9 outline (Doc 95317): https://www.vishay.com/docs/95317/do205ab.pdf
- Vishay stud-diode product list (Doc 95537): https://www.vishay.com/docs/95537/productlsit.pdf
