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The 1N4148 looks like this and a Zener diode looks the same.

What is the most recommended way to distinguish or identify them visually?

enter image description here

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    \$\begingroup\$ Close voter, how is this opinion based? \$\endgroup\$
    – Passerby
    Jan 20 at 13:19
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    \$\begingroup\$ The basic trick here is don't mix them up. Just like surface mount capacitors, once removed from their packaging and emptied on a desk they instantly become useless if mixed with other SMD capacitors. It's all about quality and common sense. \$\endgroup\$
    – Andy aka
    Jan 20 at 13:41
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    \$\begingroup\$ Classification with the use of a box with multiple lockers when one receive it? \$\endgroup\$
    – Antonio51
    Jan 20 at 13:49
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    \$\begingroup\$ the 1N4148 IS a Zener diode at 75V digikey.ca/en/products/detail/microchip-technology/… So your question ought to be how do you read codes to find the specs \$\endgroup\$ Jan 20 at 13:53
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    \$\begingroup\$ When I was OPs Mgr for a small company of 50 people we could make 10 quick turn PCB's for the designers same day. I used 35 mm film bins for the SMD and THT parts labelled in bin #s and the stock pick parts list would also list the same #. Then I had made arrays of more than 50 35 mm film containers glued to a tray. \$\endgroup\$ Jan 20 at 14:07

4 Answers 4

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That's a standard package for many diodes.

The only way to distinguish them visually is by any printed code. Or to buy them in labeled packaging from the trusted seller (digikey, mouser, the manufacturer) and don't mix them up.

Electrically you can measure the diode and put it through a few tests to get some general specs and type but trying to nail down the model would be difficult based on the sheer number of similar parts. Professionals wouldn't waste their time and hobbyists shouldn't either. The miniaturization and mass production of these commodity parts prevent that type of reuse. Just buy new ones that are properly labeled.

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There is no reliable way to distinguish between them visually, as they look the same.

However, there is an easy, reliable way of making the distinction without having to look up the manufacturer code:

Reverse bias the diode with a power supply and a high value resistor to limit current, and then measure the voltage across it.

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    \$\begingroup\$ Wouldn't necessarily work, either, if you have some high-voltage zeners. A 1N4148 will avalanche around 70 to 80 volts or so, and if you have zeners it could get mixed up with in that range you may not be able to tell the difference for sure. \$\endgroup\$
    – Hearth
    Jan 20 at 14:43
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They are typically marked.

For example, Onsemi's 1N4148 are marked "4148" with a black cathode band.

Onsemi's(Fairchild) 1N751 (5.1V Zener) are marked [logo], 51, A

Unfortunately, the similar SMT Mini-MELF package (eg. LL4148) is seldom marked and you just have to keep track of them.

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Generally you can tell because a 1N4148 is typically marked '1N4148' on the body, while a Zener diode has a different marking. You may need a magnifying glass to make sure though, because other diodes can have quite similar markings. If the markings are partially rubbed off it might be difficult to tell the difference.

Typical DO35 package Zener markings are eg. '1N4135' (a 100 V 500 mW Zener) or 'C18' (BZX55C18 18 V 500 mW Zener). Sometimes just the voltage is marked, eg '18' for 18 volts.

One thing you should not do is trust the images shown on websites. Here's a snapshot from the product page of a 1N4148 from Digikey. Note the disclaimer "Image shown is a representation only. Exact specifications should be obtained from the product data sheet."

enter image description here

And here's an "18v Zener" from electroniccenter.co.uk. It appears to be identical to Digikey's image rotated 180°, and the filename was '1n4148-29__78472.jpg'!

enter image description here

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