The DO-8 package is a JEDEC stud-mount rectifier outline, registered today under the name DO-205AA. It houses hermetic, high-current power diodes rated around 150 A with blocking voltages reaching 1400 V. The metal body measures about Ø 23.5 mm (0.93 in) across, threads onto a 3/8-24 UNF-2A stud, and carries a flexible flag lead that pushes overall length past 165 mm (6.49 in). Below are the verified DO-8 dimensions, ratings, and mounting rules.
Key takeaways
- DO-8 and DO-205AA are the same outline. DO-8 is the retired JEDEC name; DO-205AA is the current one. A datasheet may print either, or both.
- Body size: a round metal body of Ø 23.5 mm (0.93 in) max, roughly 35 mm (1.38 in) tall, seated on a 3/8-24 UNF-2A stud. A 1/2-20 UNF-2A stud and an M12 × 1.75 metric stud are factory options.
- Class: about 150 A average forward current, 600–1400 V repetitive reverse voltage, with 1600–3140 A non-repetitive surge depending on the device.
- Polarity is ordered at purchase. Standard parts put the cathode on the stud; an “R” suffix reverses it (anode on the stud). The wrong suffix bolts the wrong terminal to your heatsink.
- Torque is capped: 17 N·m on dry threads, 14.5 N·m on lubricated threads. Over-torquing cracks the glass-to-metal seal.
- On the stud ladder, DO-8 sits above DO-5 (~60 A) and below DO-9 (~300 A).
What the DO-8 package is
DO-8 is JEDEC’s Diode Outline case style 8, a stud-mount (also called bolt-mount or panel-mount) case for medium- and high-power rectifiers. The construction is a hermetic metal can with a glass-to-metal seal: one terminal is the threaded metal stud at the base, and the other is a flexible flag lead ending in a bolt hole. Both the stud and the flag lead can be fastened to a heatsink, chassis, or busbar, which is how the part sheds heat.
The naming trips people up. JEDEC retired the DO-8 designation and re-registered the outline as DO-205AA under JEP95. Retired does not mean gone: mature parts still carry the DO-8 marking, newer parts use DO-205AA, and devices released around the changeover often show both. Vishay’s own datasheets label the package “DO-205AA (DO-8)” for exactly this reason. So a “DO-8” and a “DO-205AA” of the same current and voltage rating are physically interchangeable.
[IMAGE 1: Dimensioned outline drawing of a DO-8 / DO-205AA stud rectifier, showing stud, hex base, round body, and flexible flag lead | alt: “DO-8 package stud diode dimensions outline drawing DO-205AA”]
DO-8 dimensions
The table below lists the controlled dimensions from Vishay’s DO-205AA (DO-8) outline for the 150U(R) family (Doc 95315). Values are the specified maxima, minima, or nominals; consult the manufacturer drawing for the fully toleranced figure, since minor variation exists between families and vendors.
| Feature | Metric | Imperial |
| Round package body diameter (max) | Ø 23.5 mm | 0.93 in |
| Hex base, across flats (max) | 24 mm | 0.94 in |
| Metal body height, excl. lead (max) | 35 mm | 1.38 in |
| Hex base height (max) | 17 mm | 0.69 in |
| Threaded stud length (max) | 16.5 mm | 0.65 in |
| Terminal glass-metal seal diameter (nom) | Ø 8.5 mm | 0.33 in |
| Flexible flag-lead free length (min) | 55 mm | 2.16 in |
| Overall length, stud tip to lead end | 165–170 mm | 6.49–6.69 in |
| Flexible lead cross-section | 16 mm² | — |
| Stud thread (standard / option / metric) | 3/8-24 UNF-2A / 1/2-20 UNF-2A / M12 × 1.75 | — |
Two numbers matter most in practice. The body diameter of Ø 23.5 mm sets the minimum spacing on a heatsink or busbar, and the 165–170 mm overall length is dominated by the flexible flag lead, not the can — a detail that catches people who size an enclosure from the body alone. Note that distributor “package dimensions” often quote the shipping bag, not the part; one listing gives a 162.97 mm figure that reflects the lead-and-body span, not the metal body.
Stud thread and polarity options
The standard DO-8 stud is 3/8-24 UNF-2A. Vishay’s 150U(R) family also offers a 1/2-20 UNF-2A stud, selected by an “L” suffix, and an M12 × 1.75 metric stud by factory order. Confirm the thread before you drill or tap the heatsink, because the three are not interchangeable.
Polarity is baked into the ordering code. In a Vishay VS-150U(R) part number such as VS-150UR120D, the letters decode as: U or no letter means normal polarity, cathode connected to the stud; R means reverse polarity, anode connected to the stud. The die is identical either way — only the internal connection flips. The stud is the terminal you bolt to your heat path, so the suffix decides whether the stud sits at cathode or anode potential in your circuit. Get it wrong and the part mounts fine but blocks the wrong direction.
[IMAGE 2: Side-by-side diagram of stud-cathode (standard) versus stud-anode (“R” suffix) DO-8 diodes | alt: “DO-8 stud cathode versus stud anode R suffix polarity”]
Electrical envelope DO-8 hosts
DO-8 is an outline, not a single part, so ratings depend on the device inside. Two representative families anchor the range:
| Device family | IF(AV) | VRRM range | IFSM (peak, non-rep.) | VFM | Notes |
| Vishay VS-150U(R)..D | 150 A at 125 °C | 600–1200 V | 3000 A (50 Hz) / 3140 A (60 Hz) | 1.47 V at 600 A, 25 °C | Standard recovery, stud cathode or anode |
| Microsemi 1N3289 series | High-current | up to 1400 V | 1600 A | — | Glass-passivated, high-reliability |
Vishay’s 150U(R) datasheet also specifies a slope resistance of 0.97 mΩ, a threshold voltage of 0.80 V, and an I²t for fusing of 45 kA²s at 50 Hz — the numbers you feed a fuse-coordination or surge calculation, and the numbers no distributor page carries. The Microsemi 1N3289 is the classic military-grade DO-8 part: a glass-passivated silicon rectifier with a 1600 A surge rating and blocking voltage to 1400 V.
Mounting, torque, and thermal interface
Torque control keeps the hermetic seal intact. Vishay caps mounting torque at 17 N·m for dry (unlubricated) threads and 14.5 N·m for lubricated threads, both with a 0/−20% tolerance. Lubricated threads convert more torque into clamp force, which is why their limit is lower. Exceeding either figure risks cracking the glass-to-metal seal and destroying the hermetic package.
For heat, the part specifies a junction-to-case thermal resistance of 0.3 K/W (DC) and a case-to-heatsink resistance of 0.1 K/W on a smooth, flat, greased surface. Mount the stud to a flat, deburred, thermal-greased seating area, and if the layout allows, clamp the flag lead to the heat path too — both terminals conduct heat. Approximate part weight is 130 g, heavy enough that vibration-prone assemblies need the lead supported, not left cantilevered.
Where DO-8 sits in the stud-diode family
DO-8 is one rung on the JEDEC stud-rectifier ladder. Current class scales with body and stud size:
| Package (old / JEDEC) | Typical IF(AV) class | Stud thread | Example device |
| DO-4 / DO-203AA | ~12–20 A | 10-32 UNF | Vishay 12FL (12 A) |
| DO-5 / DO-203AB | ~40–60 A | vendor-specific | Vishay VS-1N1183 (60 A / 1000 V) |
| DO-8 / DO-205AA | ~150 A | 3/8-24 UNF (1/2-20 option) | Vishay VS-150U..D; 1N3289 |
| DO-9 / DO-205AB | ~240–400 A | vendor-specific | Vishay 240U / 400U (320–400 A) |
| DO-30 / DO-205AC | ~200 A, higher voltage | vendor-specific | Vishay SD200N/R (200 A, 1600–2400 V) |
If a design outgrows DO-8, DO-9 (DO-205AB) is the next step up in current; DO-30 (DO-205AC) trades some current headroom for higher blocking voltage in the same physical family.
[IMAGE 3: Relative size comparison of DO-4, DO-5, DO-8, and DO-9 stud rectifiers | alt: “stud diode package size comparison DO-4 DO-5 DO-8 DO-9”]
Sourcing, obsolescence, and second sources
DO-8 is a legacy outline, and much of the catalog is now NRND or discontinued — Vishay’s VS-150UR80D, for instance, is being dropped by the manufacturer. Several houses build form-fit-function replacements for the 1N3289 and Vishay stud rectifiers, including New Jersey Semiconductor, Naina Semiconductor, Digitron, and AS Energi. When you cross-reference, match five things, not just the DO-8 label: average forward current, repetitive reverse voltage, surge rating, stud thread, and polarity suffix.
One caution for the high-reliability parts: the 1N3289 series is a military-grade, glass-passivated device that shows up on obsolescence markets, where counterfeits and re-marked commercial parts appear. Buy hi-rel DO-8 rectifiers from franchised distributors or the original maker, and verify lot traceability for anything going into aerospace or defense hardware.
FAQ
Is DO-8 the same as DO-205AA?
Yes. DO-8 is the older JEDEC designation and DO-205AA is the current one for the identical stud-mount outline. Manufacturers may print either name, or both together, on the datasheet. Parts of the same current and voltage rating are physically interchangeable regardless of which label is used.
What are the dimensions of a DO-8 diode?
The metal body is about Ø 23.5 mm (0.93 in) across and roughly 35 mm (1.38 in) tall, on a 3/8-24 UNF-2A stud with a threaded length up to 16.5 mm (0.65 in). Including the flexible flag lead, overall length runs 165–170 mm (6.49–6.69 in), per Vishay’s DO-205AA outline drawing.
What stud thread does a DO-8 diode use?
The standard thread is 3/8-24 UNF-2A. Vishay’s 150U(R) family also offers a 1/2-20 UNF-2A stud (an “L” suffix option) and an M12 × 1.75 metric stud by factory order. The three are not interchangeable, so confirm the thread against the specific part number before machining the heatsink.
What is the mounting torque for a DO-8 stud diode?
Vishay caps it at 17 N·m for dry threads and 14.5 N·m for lubricated threads, with a 0/−20% tolerance. Torque beyond that risks cracking the glass-to-metal seal and breaking the hermetic package. Mount to a flat, greased surface and use a calibrated torque wrench.
What does the “R” suffix mean on a DO-8 rectifier?
It denotes reverse polarity. A standard part connects the cathode to the stud; an “R” suffix connects the anode to the stud instead. The die is the same — only the internal connection is flipped — so the suffix tells you which terminal is at stud potential when the part is bolted down.
How much current can a DO-8 package handle?
Common DO-8 rectifiers carry about 150 A average forward current, such as the Vishay VS-150U(R) family at 125 °C case temperature. Non-repetitive surge ratings reach roughly 1600–3140 A depending on the device. The exact rating always comes from the specific part’s datasheet, not the package name.
Bottom line
If a part in front of you is marked DO-8 or DO-205AA, treat it as a Ø 23.5 mm stud rectifier in the ~150 A class: confirm the stud thread (assume 3/8-24 UNF unless an “L” or metric option applies), read the polarity suffix to see whether the stud is cathode or anode, torque to no more than 17 N·m on dry threads, and mount it to a flat, greased heatsink sized for a 0.3 K/W junction-to-case path. For a replacement, match current, voltage, surge, thread, and polarity — not the package label alone. For a clean-sheet design, reach for DO-8 only when you specifically need the stud form factor or a drop-in for legacy high-reliability hardware; otherwise a modern module or press-fit rectifier will mount and cool more easily.
