1N4148 Small Signal Diodes

If your board calls for a small, fast glass switching diode with wire leads, and the old part is a 1N4148 in a DO-35 glass body, this is the part to order. It switches fast, it handles small signals cleanly, and it fits through-hole boards that the tiny surface-mount version cannot fit. It does not fit jobs that need more than 100 V peak reverse voltage, more than 300 mA of steady current, or a surface-mount pad footprint. Check the checks below before you order, so the body, the leads, and the limits all match your board.

This is an original, high-quality part.

What it does

A diode lets current flow one way and blocks it the other way. This 1N4148 diode does that job at high speed. When the signal flips, it stops passing current in the old direction within a few billionths of a second. That is why repair techs use it for fast switching, for shaping a waveform, for clamping a signal, and for routing a small signal to the right place on a board.

This is a small signal diode, not a power diode. It is made for low current signal circuits, such as control boards, logic circuits, and the small signal sections of power supplies and inverter boards. It is not made to carry large power currents. The glass body has a black band on one end. That band marks the cathode end. Put it in the wrong way round and the circuit will not work as planned.

Key features

• Fast switching for small signal work
• DO-35 glass body with wire leads for through-hole boards
• 100 V peak reverse voltage limit
• 300 mA steady forward current limit
• 500 mW power limit at cool lead temperature
• Low forward voltage: 1 V at most at 10 mA
• Tiny leakage: 25 nA at most at 20 V
• Small capacitance: 4 pF at most, so it loads a fast signal line only a little
• Black band marks the cathode end, so the fit direction is easy to see

Checks before you order

• Package: your board must have through holes for a DO-35 glass body with wire leads. If your board has only small surface pads, this leaded part will not fit without rework. Measure the old part or match it against the holes on your board.
• Polarity: match the black band to the band mark on your board print. The band end is the cathode. A diode put in backwards will block the signal it should pass.
• Voltage: the peak reverse voltage must stay at or below 100 V, and the steady reverse voltage at or below 75 V. If your circuit runs higher, this part is the wrong pick.
• Current and power: the steady current must stay at or below 300 mA, the average current at or below 150 mA, and the power inside the 500 mW limit in the table below. If your circuit pushes more, pick a power diode, not this small signal part.
• Speed: this part’s recovery time is 4 ns under one test setup and 8 ns under another setup in its own data. Both numbers are real; they come from different test conditions. For plain fast switching work, either number means the same thing in practice: this diode switches very fast.
• Marking: the code V4148 on the ordering data points to this same 1N4148 DO-35 part. Read the old part’s body and board print together, not the code alone.

Specifications

All figures below are for the DO-35 1N4148 diode at +25 °C unless noted. No figure here was guessed.

If this part is not available, use one of these instead

Do not pick a random diode with a close name. Use a part with the same job and the same limits, and check the fit first.

Substitutes you can buy from this shop

• 1N4148 A2 SMD High Speed Switching Diode SOD-123 — practical substitute, not an exact drop-in. It does the same 1N4148 diode job with the same 100 V and 300 mA headline limits. But it is a surface-mount part, not a leaded part. It solders onto pads, while this DO-35 part fits through holes. Its power limit is lower at 400 mW, and its capacitance is lower at 2.0 pF. Use it only if your board has SOD-123 pads or you can rework the fit, and check the power and capacitance against your circuit first.

Warning: never swap on the part number alone. Check package and pads, soldering method, board space, voltage, current, power, and the polarity band first. If any one of those does not match, do not swap.

Other names for the same part (good to know)

Shoppers and repair techs call this same part by a few names. 1N4148 is the part number. 1N4148 DO-35 is the part number with its glass body size. DO-35 switching diode and small signal diode are the plain names buyers use for this part. 1N4148 fast switching diode is the name buyers use when they need its speed. V4148 is the code in the ordering data for this same DO-35 part. If you see a small glass diode with a black band on a through-hole board, and the circuit needs a fast 1N4148, this page is the right match.

Frequently Asked Questions

What is the difference between this DO-35 part and the small SMD version?

They do the same diode job, but they fit differently. This DO-35 part has wire leads and fits through holes in the board. The SMD version solders onto surface pads and has no leads. Their power and capacitance limits also differ a little, so check the table before you swap.

Which way round does this diode go?

The black band on the glass body marks the cathode end. Fit the new diode with its band in the same place as the old diode’s band. If it goes in backwards, it will block the signal it should pass.

Why does the recovery time show two numbers, 4 ns and 8 ns?

Both numbers come from the same data, measured under two different test setups. The 4 ns number comes from a 10 mA, 6 V test, and the 8 ns number comes from a 10 mA test with different test currents. For plain fast switching work, both mean the diode switches very fast.

Can I use this diode for high current power work?

No. This is a small signal diode. Its steady current limit is 300 mA and its power limit is 500 mW. For high current power work you need a power diode or rectifier with higher limits, not this part.

What should I check before I order?

Check five things: package (DO-35 glass body with leads), polarity (match the black band), voltage (100 V peak at most), current and power for your circuit, and the old part’s body size.

What is the price of this part?

Check the live price on the website. The price shown on the product page is the current one.

You can view and download the datasheet for this part from the Datasheet button on this page.

Use note kept from the old page: this part was listed before for solar inverter repairing and other precision circuits, for signal processing, waveform shaping and rectification, in high-frequency circuits, logic gates and general-purpose rectification, and that use still stands.