Idenfitying a diode

[Pcmaker]

I posted a problem about my DeWalt battery charger here a few days ago and I found a bad diode today right next to the transformer, buried under some glue. It's hard to read and hard to figure out which number/letter is the starting one.

I'm getting 0.000 either way I test the diode with my multimeter.


I think the correct order is BYV26EGP and has "451" under it

I'm going to replace this diode to see if this is the problem.  datasheet:

https://www.vishay.com/docs/88554/byv26dgp.pdf

I'm going to Fry's electronics tomorrow to replace this diode. What characteristics should I be looking for? Max voltage and size?  Is "451" the voltage you're supposed to get when you test it with the multimeter's diode function?

[ebclr]

Very important
IF(AV) 1.0 A
VRRM 800 V, 1000 V

secondary
IFSM 30 A
trr 75 ns

This diode can be replaced with many types, nothing special

[Old Don]

451 is most likely a date code - 51 week of 2014, 2004 or 1994 or .....

A multimeter does not put out voltage equal to a diode's breakdown voltage. It measures resistance measured by reading the voltage dropped across an internal resistor from the internal battery powering the meter. No current flow equals high resistance and max current (as designed) equals a short.

You need a diode designed to handle the current flow of your charging circuit plus also exceeding the highest voltage the diode will see - if it is direct off mains then at least 1.5 times input voltage. Since a 1000 volt diode costs about the same as a 200 or 400 volt diode in many cases you can fudge and just go with a 1000 volt diode. But the current rating can not be exceeded or you will be back to buy a 2nd replacement soon.

A 1N4007 is a one amp diode rated for 1000 volts and is easy to find. Don't know if it is what you need or not.

[Pcmaker]

This is the only 1000v Fry's had, but it's 3amp max

Wills this work?

[Pcmaker]

This is the only 1000v Fry's had, but it's 3amp max
Wills this work?

It's not a fast recovery. Maybe it doesn't matter for mains rectification, but if you use it for other purposes, it may end up glowing red hot.
BYV26 is widely used in flyback converters as leakage energy absorption diode, and if you put a slow, mains diode (not fast recovery), it will blow up in no time.

Please post a pic of your charger, and I can see if it's a mains diode or a flyback/forward diode.

The bad diode was buried under all that white epoxy right above the transformer, right next to the R3 resistor and the sleeved resistor.

[Pcmaker]

The bad diode was buried under all that white epoxy right above the transformer, right next to the R3 resistor and the sleeved resistor.

DON'T replace with your Fry's diode, it will literally fry the circuit in no time!
You need an ultra fast recovery diode for the job.

How do you know if a diode is an ultra fast recovery diode or not? Is there a symbol?

[lilshawn]

it's specified in the datasheet. typically UFR diodes are used on the output of SMPS because of the high switching frequencies used. A regular diode does not switch fast enough to block.

[Pcmaker]

Are Ultra Fast Rectifier diodes the same as Ultra Fast Recovery diodes?

[Pcmaker]

How do you know if a diode is an ultra fast recovery diode or not? Is there a symbol?

Read the datasheet of the diode, it has a trr (reverse recovery time) spec.

It only has to have a trr spec or does it have to be faster than certain amount of time/nanoseconds to be considered a UFR diode?

[Pcmaker]

How do you know if a diode is an ultra fast recovery diode or not? Is there a symbol?

Read the datasheet of the diode, it has a trr (reverse recovery time) spec.

It only has to have a trr spec or does it have to be faster than certain amount of time/nanoseconds to be considered a UFR diode?

Don't know the exact threshold, but I would say 500ns for fast recovery, and 100ns for ultra fast recovery.

Thanks!

I'm very new at this, but I'm learning multiple different things every day and I'll eventually become competent and more importantly, not have to bother people asking so many dumb questions.

[ElektroQuark]

Do they really sell super cheap components ONE BY ONE in blister package?

The handling and packaging will increase the price by a hundred.

[Pcmaker]

Thinking of getting this as a replacement. I wish I could only buy a couple pieces in town. If Fry's doesn't carry these, then I'm guessing nobody in the city does. I don't want to pay 15 bucks total for a set of them from Amazon.

https://www.amazon.com/McIgIcM-200pcs-Standard-Through-DO-204AL/dp/B071KKHBGC/ref=sr_1_1?ie=UTF8&qid=1508755704&sr=8-1&keywords=UF4007

[Mjolinor]

Rob one from something old and broken. Most modern things will have one in.