The DO-27 package is the 3 A axial plastic body used for the 1N5400 series, FR300 series and 1N5820 Schottky family. Diodes Incorporated dimensions it at 5.00 mm to 5.60 mm body diameter, 8.50 mm to 9.50 mm long, with 1.20 mm to 1.30 mm leads at least 25.4 mm on each end. Almost every listing calls it “DO-27 (DO-201AD)”. Those two outlines are not identical.

Key takeaways

• DO-27 per the Diodes Incorporated drawing dated 2019-10-14: body 5.00 mm to 5.60 mm diameter, 8.50 mm to 9.50 mm long, leads 1.20 mm to 1.30 mm diameter, 25.4 mm minimum each end.
• DO-201AD is a narrower envelope — 4.80 mm to 5.30 mm diameter and 7.20 mm to 9.50 mm long per Vishay document 88516, rev. 19-Dec-2025.
• Diodes Incorporated publishes DO-27, DO-27 (Type YJ) and DO-201AD as three separate outlines. Vishay does not use the DO-27 name at all.
• A DO-27 part can be up to 0.3 mm fatter than the DO-201AD limit. Lead diameter and pitch are the same, so it still fits the holes — check clearance, not the footprint.
• Current ratings use different references. The 1N5400 is 3.0 A at 12.5 mm lead length and 105 °C lead temperature; Fairchild rates the 1N5820 at 3.0 A with 9.5 mm leads at 95 °C ambient.
• Published R(thJA) for the same 1N5822 die ranges from 28 °C/W to 80 °C/W depending on whose measurement conditions you read.

What the DO-27 package actually is

DO-27 is an axial through-hole outline for a molded plastic diode body carrying roughly 3 A. It sits one size above DO-41 and is the standard home for the 1N5400 rectifier series, the FR300 fast-recovery series and the 1N5820 Schottky series. The outline fixes the envelope only; voltage, current and recovery time come from the die.

The confusion starts with the naming. Distributors write “DO-27/DO-201AD” as though the two are one part. Diodes Incorporated does not: its package index lists DO-27, DO-27 (Type YJ) and DO-201AD as three separate drawings.

DO-27 vs DO-201AD dimensions, side by side

These are drawing figures, not measurements. The DO-27 column comes from the Diodes Incorporated drawing dated 2019-10-14; the DO-201AD column from the Vishay outline printed in document 88516.

Feature	DO-27	DO-201AD
Body diameter	5.00 mm to 5.60 mm	4.80 mm to 5.30 mm
Body length	8.50 mm to 9.50 mm	7.20 mm to 9.50 mm
Lead diameter	1.20 mm to 1.30 mm	1.22 mm to 1.32 mm
Lead length, each end	25.40 mm minimum	25.40 mm minimum
Polarity marking	Cathode line by marking	Color band denotes cathode
Unit weight (1N5404-E3/54)	—	1.1 g

The gap is real but small: a DO-27 body can be 0.3 mm fatter than any legal DO-201AD, and its minimum length is 1.3 mm longer. Leads are effectively identical, so hole size and pitch do not change. What changes is body clearance — under a heatsink, on a tight axial pitch, or inside a potted assembly.

Distributor data reflects the mess. RS lists the Taiwan Semiconductor FR307G as “DO-201AD” with a diameter of 5.6 mm — outside the DO-201AD maximum and exactly at the DO-27 maximum. Trust the drawing, not the attribute field.

Rating conditions matter more than the envelope

An axial diode moves most of its heat out through the leads. Vishay rates the 1N5400 series at 3.0 A with 0.5 in (12.5 mm) lead length at a lead temperature of 105 °C, and quotes R(thJA) of 20 °C/W measured at 9.5 mm lead length with 20 mm × 20 mm copper heat sinks on the board. Change either condition and the rating moves.

Its derating curve is plotted for lead lengths of 12.7 mm, 7.9 mm and 6.4 mm, plus a separate ambient-temperature curve at 9.5 mm. Most summaries reproduce a single “3 A” number and drop all four conditions.

The Schottky parts are worse. Fairchild rates the 1N5820 series at 3.0 A with 3/8 in leads at 95 °C ambient and quotes 28 °C/W with 3.6 W dissipation. STMicroelectronics quotes 80 °C/W for the same generic device at 10 mm lead length. Both numbers are correct for their own test setup, and a designer who mixes them will be wrong by a factor of nearly three.

Worked example: a 1N5408 at 2 A

Take a 1N5408 passing 2.0 A average in a mains rectifier. Maximum forward voltage is 1.2 V at 3.0 A, so conduction loss lands near 2.6 W with the half-wave form factor included. At the Vishay figure of 20 °C/W that is a 52 °C rise — but only with 20 mm × 20 mm of copper per lead and 9.5 mm leads.

Halve the copper and the effective resistance climbs sharply, pushing the junction from roughly 100 °C toward the 150 °C limit. The copper is part of the component.

Choosing a die in this body

Series	Type	I(FAV) and condition	V(RRM)	V(F) max	I(FSM)
1N5400-1N5408	Standard	3.0 A, 12.5 mm lead, TL = 105 °C	50 V to 1000 V	1.2 V at 3.0 A	200 A
FR301-FR307	Fast recovery	3.0 A	50 V to 1000 V	—	—
1N5820-1N5822	Schottky	3.0 A, 9.5 mm lead, TA = 95 °C	20 V / 30 V / 40 V	0.475 V to 0.525 V at 3.0 A	80 A

Two conditions to carry. The Schottky parts stop at 125 °C junction, not 150 °C, and leak milliamps rather than microamps — ST quotes 2 mA at 25 °C for the 1N582x against 5.0 µA for the 1N5400 series.

Sourcing and process traps

• Solder windows disagree across suppliers of the same generic part: 275 °C for 10 s per JESD 22-B106 (Vishay 1N5400), 260 °C for 10 s (Kingtronics FR301-FR307), 250 °C for 10 s (MDD 1N5404). Qualify to the lowest number on your AVL.
• Vishay states the 1N5400 series is not AEC-Q101 qualified. If the board goes in a vehicle, you need a supplier who says otherwise in writing.
• RS listed the Taiwan Semiconductor FR307G in stock at roughly £0.17 per unit in hundreds, falling to about £0.11 at 2,000 pieces.
• Watch for withdrawn lines. Rapid flagged the DC Components 1N5408 in DO-27 as remaining stock only, no replenishment planned.
• This package is heavily counterfeited: it is cheap and generic. Buy franchised, and caliper the body diameter against the drawing if a lot looks wrong.

Design mistakes that cause returns

• Assuming DO-27 and DO-201AD are dimensionally identical. The body can be 0.3 mm fatter. That matters under a clamp, a shield or a conformal coat.
• Copying a 3 A rating without the lead length. The 1N5400 figure assumes 12.5 mm leads at 105 °C lead temperature.
• Sizing copper by habit. The 20 °C/W figure is measured with 20 mm × 20 mm copper heat sinks. Smaller pads mean a higher number.
• Mixing thermal figures across suppliers. 28 °C/W and 80 °C/W both describe a 1N5822.
• Treating the Schottky as a drop-in for the silicon part. It stops at 125 °C and leaks three orders of magnitude more.
• Bending leads at the body. Support the lead so the epoxy-to-lead interface does not take the strain.

Frequently asked questions

What is a DO-27 package?

DO-27 is an axial through-hole outline for a molded plastic diode rated near 3 A. Per the Diodes Incorporated drawing, the body is 5.00 mm to 5.60 mm in diameter and 8.50 mm to 9.50 mm long, with 1.20 mm to 1.30 mm leads at least 25.4 mm on each end. A cathode line marks polarity.

Is DO-27 the same as DO-201AD?

Not exactly. They are close enough that suppliers write “DO-27/DO-201AD” and parts interchange electrically, but the drawings differ. DO-27 allows a 5.60 mm body diameter; DO-201AD stops at 5.30 mm. Lead diameter and length match, so the footprint is shared even when the body is not.

What are the dimensions of a DO-27 diode?

Body diameter 5.00 mm to 5.60 mm, body length 8.50 mm to 9.50 mm, lead diameter 1.20 mm to 1.30 mm, and lead length 25.40 mm minimum on each end, per the Diodes Incorporated package drawing dated 2019-10-14. All figures are drawing limits, not typical measured values.

How much current can a DO-27 diode handle?

About 3 A average, but only under stated conditions. Vishay rates the 1N5400 series at 3.0 A with 12.5 mm lead length at a 105 °C lead temperature. Surge capability is 200 A for an 8.3 ms half sine on the silicon parts and 80 A on the 1N5820 Schottky series.

What is the difference between DO-27 and DO-41?

DO-41 is the 1 A body at roughly 2.7 mm diameter with 0.86 mm leads. DO-27 is the 3 A body at up to 5.6 mm diameter with 1.3 mm leads. The thicker lead is where most of the extra current capability comes from, since axial diodes conduct heat out through the leads into the copper.

What to do next

If you are laying out a new board, specify DO-201AD but design body clearance to the DO-27 envelope of 5.6 mm by 9.5 mm. That combination accepts either outline from any supplier. Budget 12.5 mm of lead and 20 mm × 20 mm of copper per pad if you need the full 3 A. If your enclosure is already tight around a 5.3 mm body, verify the drawing on every alternate before approving it.

External references

• Diodes Incorporated DO-27 package outline: https://www.diodes.com/assets/Package-Files/DO-27.pdf
• Diodes Incorporated DO-201AD package outline: https://www.diodes.com/assets/Package-Files/DO-201AD.pdf
• Diodes Incorporated package outlines and pad layouts index: https://www.diodes.com/design/support/packaging/diodes-packaging/diodes-package-outlines-and-pad-layouts
• Vishay 88516, 1N5400 thru 1N5408: https://www.vishay.com/docs/88516/1n5400.pdf
• Vishay 88526, 1N5820 / 1N5821 / 1N5822: https://www.vishay.com/docs/88526/1n5820.pdf
• STMicroelectronics 1N582x Schottky rectifier: https://www.st.com/resource/en/datasheet/1n5822.pdf

Image placeholders

• IMAGE 1: Macro photograph of a 1N5408 beside a 1N4007 on a steel rule, cathode bands aligned. Alt: “DO-27 package axial diode dimensions compared with a DO-41 body on a scale rule”
• IMAGE 2: Overlaid mechanical drawings of DO-27 and DO-201AD showing the 5.60 mm and 5.30 mm diameter limits. Alt: “DO-27 versus DO-201AD outline drawing showing 5.6 mm and 5.3 mm body diameter limits”
• IMAGE 3: Board photo comparing 20 mm x 20 mm copper pads against minimal pads for the same axial part, with a thermal overlay. Alt: “Effect of copper pad area on DO-27 diode junction temperature at 20 mm square versus minimal pads”
• IMAGE 4: Calipers measuring the body diameter of an axial rectifier against the drawing limits. Alt: “Measuring DO-27 axial diode body diameter with calipers to verify the 5.6 mm limit”

Internal link placements (fpga.io)

• INTERNAL LINK: “DO-41 package” -> DO-204AL axial diode outline and derating
• INTERNAL LINK: “junction-to-ambient thermal resistance” -> how R(thJA) is measured and why board copper changes it
• INTERNAL LINK: “fast recovery rectifiers” -> choosing standard, fast and ultrafast diodes
• INTERNAL LINK: “AEC-Q101 qualification” -> what AEC-Q101 covers and when you actually need it
• INTERNAL LINK: “counterfeit component detection” -> incoming inspection checks for discrete semiconductors