1N4148 PCB Design Guide: Footprint, Pinout, and Alternatives
100 V small-signal switching diode; multi-source jellybean
The 1N4148 is the default small-signal switching diode: a 100 V, glass-bodied DO-35 part with a 4 ns maximum reverse recovery that has been clamping, steering, and OR-ing logic-level signals for six decades. If a schematic just says "diode" with no further thought, this is usually the part it means.
It is a multi-source jellybean, and that matters more than it sounds. This page cites Vishay's datasheet (document 81857, Rev 1.6), which rates forward continuous current IF at 300 mA and average current IF(AV) at 150 mA — while Nexperia rates their 1N4148 at 200 mA IF. Same part number, different guaranteed limits. When a rating is near the edge of your design, check the datasheet of the manufacturer actually on your BOM.
The mistakes that kill 1N4148s are predictable: pressing a small-signal diode into rectifier duty, clamping a relay coil that draws more than the diode can carry, cracking the glass body by bending leads at the case, and forgetting that the SMD equivalents are separate part numbers with tighter power limits. Each is covered below.
What breaks boards
Small-signal only — it is not a rectifier
This is a 100 V part rated 300 mA forward continuous / 150 mA average on Vishay's sheet, built for speed (4 ns recovery), not power. Using it where a 1N4007 or a Schottky rectifier belongs — power-supply rectification, motor circuits, anything carrying hundreds of milliamps sustained — burns it. If the current is measured in amps, pick a rectifier; keep the 1N4148 for logic-level switching, clamping, and signal steering.
Ratings differ by manufacturer — check the brand on your reel
Vishay guarantees IF 300 mA continuous and IF(AV) 150 mA; Nexperia's 1N4148 datasheet states 200 mA IF. Both are legitimate 1N4148s with different guaranteed limits, and distributors will substitute brands freely. Design to the datasheet of the manufacturer you actually buy, or to the most conservative figure if the source may vary.
Fine as a flyback clamp — at small coil currents
The 4 ns recovery makes the 1N4148 a good clamp across small relay and signal-level coils, and it is the standard choice there. But the diode must carry the full coil current when the driver switches off: check the coil's operating current against the forward current rating (and the 2 A / 1 us IFSM figure covers only the brief surge, not sustained conduction). Larger relay or solenoid coils get a 1N4007- or 1N5819-class diode instead.
SMD migration: 1N4148W and 1N4148WS are separate MPNs
The surface-mount equivalents are the 1N4148W in SOD-123 and the 1N4148WS in SOD-323 — same die class, but each has its own datasheet and the smaller packages derate power dissipation. Do not treat them as footprint variants of one part number: pick the package deliberately and check the ratings on that specific datasheet.
The glass body cracks if you bend leads at the case
The DO-35 package is a glass tube, and bending the leads right at the body stresses the glass-to-lead seal — cracks can be invisible and show up later as intermittent or open diodes. Bend leads at least 2 mm away from the body, supporting the lead between body and bend, and give the footprint enough lead length to allow it.
Forward drop: about 0.7 V typical, but 1 V is the guaranteed limit
At 10 mA the typical forward curve runs around 0.7 V, but Vishay's guaranteed maximum is 1 V at that current. Worst-case analysis for OR-ing diodes, level clamps, and anything with tight headroom must use the 1 V limit, not the typical figure. Where the drop genuinely matters, compare against a BAT54-class Schottky with its lower forward voltage.
Key specifications
| Parameter | Value | Source |
|---|---|---|
| VRRM | 100 V | Vishay 81857 Rev 1.6, Absolute Maximum Ratings |
| IF average | 150 mA (IF(AV), VR = 0); forward continuous current IF 300 mA | Vishay 81857 Rev 1.6, Absolute Maximum Ratings |
| IFSM surge | 2 A (tp = 1 us) | Vishay 81857 Rev 1.6, Absolute Maximum Ratings |
| trr | 4 ns max (IF = 10 mA, VR = 6 V, iR = 0.1 x IR, RL = 100 ohm); 8 ns max (IF = IR = 10 mA, iR = 1 mA) | Vishay 81857 Rev 1.6, Electrical Characteristics |
| VF at 10 mA | 1 V max (guaranteed limit; typical forward curve runs ~0.7 V at 10 mA) | Vishay 81857 Rev 1.6, Electrical Characteristics and Forward Characteristics figure |
| Package options | DO-35 (DO-204AH) glass, TR (tape/reel) or TAP (ammopack); SMD migration = 1N4148W (SOD-123) / 1N4148WS (SOD-323), separate MPNs | Vishay 81857 Rev 1.6, Mechanical Data and Parts Table |
Verified against the manufacturer datasheet on 2026-07-09. Confirm the current revision before production use.
Alternatives
- BAT54S — series-pair Schottky with a lower forward drop for clamps and OR-ing where the 1N4148's drop costs too much headroom — but only 30 V rated.
- 1N4148W / 1N4148WS — the same die class in SOD-123 and SOD-323 for surface-mount boards; separate MPNs with their own datasheets and tighter power derating.
- 1N5819 — 1 A Schottky for actual power rectification and larger flyback clamps — the right part when the current is beyond small-signal territory.
Common questions
- What is the maximum current of a 1N4148?
- On Vishay's datasheet: 300 mA forward continuous (IF), 150 mA average (IF(AV)), and a 2 A surge for 1 us. Note that other manufacturers rate their 1N4148 differently — Nexperia specifies 200 mA IF — so check the sheet for the brand you actually buy.
- 1N4148 vs 1N4007 — which one do I need?
- They solve different problems. The 1N4148 is a fast (4 ns recovery) small-signal switching diode for clamps, signal steering, and logic-level work; the 1N4007 is a slow power rectifier for mains-frequency rectification and higher currents. Using a 1N4148 as a rectifier burns it; using a 1N4007 in a fast switching path is too slow.
- What is the SMD equivalent of the 1N4148?
- The 1N4148W in SOD-123 and the smaller 1N4148WS in SOD-323. They are the same die class but separate part numbers with their own datasheets, and the smaller packages derate power dissipation — verify ratings on the specific datasheet rather than assuming DO-35 numbers carry over.
- Can I use a 1N4148 as a flyback diode?
- Yes, for small relay and signal-level coils — the 4 ns recovery is well suited to clamping. The constraint is current: the diode carries the full coil current at turn-off, so it must stay within the forward current rating (300 mA continuous on Vishay's sheet). Larger coils need a 1N4007- or 1N5819-class diode.