Relay Coil Diode Specs

[Ken1]

I have a circuit board with a Panasonic JW1FSN-DC12V relay on it. This relay makes use of an external surface mount diode across the coil. This diode is shorted. It has no markings on it. It is orange in color with a black band to indicate the cathode. Can someone suggest what kind of diode I can use to replace it and see if the board will work?

 

[ronsimpson]

The relay coil is for 44mA and 12V. The diode will not see more than that.
As for diode voltage, look for 50V to 100V.
As for diode current, look for 50mA to 1A.
You can try to identify the size of the case of the diode.
digikey This link will take to Digikey.com with some search numbers set up for you. I entered diode, SMT, 50 to 100V, 100mA to 1A, standard, in stock.
I don't know what the part looks like. Here is an example of what might work. 1N4148WX-TP

 

[ChrisP58]

The data says the coil current should be about 44mA, so any diode with a current rating higher than that, and a voltage rating higher than the coil voltage should work. But that's with no margin. personally, I'd choose a minimum 100mA at 50 Volts. But it's OK to use a diode with higher ratings.

https://na.industrial.panasonic.com...echanical-power-relays/series/1974/model/2186

But you'll also want to match the footprint of the existing part.

I don't think that I've ever seen a surface mount diode in an orange case.

 

[Ken1]

The case is actually clear cylindrical "glass" I assume and the semiconductor material inside is the same orange color as many zener diodes.

 

[Nigel Goodwin]

Have you removed the diode and tested it?, it would be extremely unusual for such a diode to go S/C (I've never seen one do so) - but in the event it has?, it's pretty non-critical, a simple 1N4148 small diode is all that's needed for a small relay.

 

[Ken1]

The relay did not want to work and in circuit tests revealed less than 1 ohm for the coil, so I removed the relay assuming it's bad and re-tested it and got 265 ohms. A resistance test of the coil's solder pads still showed the short. Removing one end of the diode showed that it is shorted and the rest of the circuit has a high resistance reading.

 

[MaxHeadRoom78]

I keep IN4007 & UF4007 on hand, they cover a lot of bases,

 

[eTech]

The relay did not want to work and in circuit tests revealed less than 1 ohm for the coil, so I removed the relay assuming it's bad and re-tested it and got 265 ohms. A resistance test of the coil's solder pads still showed the short. Removing one end of the diode showed that it is shorted and the rest of the circuit has a high resistance reading.

I'm curious as to the diode part number(?).

 

[Nigel Goodwin]

I'm curious as to the diode part number(?).

A SM diode is unlikely to have a number printed on it, many SM components are completely anonymous

 

[schmitt trigger]

The case is actually clear cylindrical "glass" I assume and the semiconductor material inside is the same orange color as many zener diodes.

That is called a MELF package. Metal Electrode Leadless Face.

 

[ChrisP58]

The case is actually clear cylindrical "glass" I assume and the semiconductor material inside is the same orange color as many zener diodes.

Then it's probably this part.
https://www.digikey.com/en/products/detail/microchip-technology/1N4148UR-1/4377991

 

[crutschow]

The diode could be shorted if somehow a reverse voltage was applied to the relay coil

 

[Ken1]

I replaced the diode with a 1N4148 and the relay works now. Don't know why the diode failed. It does resemble the one in the Digikey link. Thanks everyone!