Diodes and Their Markings

There are loads of cross references for semiconductors on the web. Here's one you could start with.

Can you do a little circuit analysis, and replace with diodes that match the results? Forward voltage and current are probably the only specs that are relevant for a simple power supply.

Good luck.

Sorry, but you might just happen to have a batch of custom diodes there. Many a manufacturer has had custom parts built to meet esoteric requirements. These requirements can range from selecting a deliberate failure mode with a precise MTBF, to preventing a competitor from reverse engineering their product. You may even have "one off" parts that are just one parameter off of the standard parts they were originally meant to be. These parts are often sold at a considerable discount and referenced only at the time of sale to the parts that they are close to.

But this begs another question. Why replace just these 5 diodes and not the whole supply? Many large volume electronic systems (particularly power supplies) have had all of the component's MTBF carefully selected so that when any one critical component dies, most of the remaining components in the system are close to their end, too.

If you do go the route of replacing be sure to pay attention to the frequency of operation. Most general purpose rectifier diodes are speced for 60 hz but the switching supply you are working on most likely is working at a much higher frequency. Good Luck

1Nxxx means one Junction so it is a diode. like wise 2Nxxxx means 2 junctions that is a transistor.

1N4001 is 1A diode about 200V PIV (peak inverse voltage) 1N4007 PIV is 700V and so on.

visit: http://www.tpub.com/neets/book7/24k.htm

and: http://en.wikipedia.org/wiki/Diode

Most SMD components are now so tiny that it would be impossible to apply a full part number so a short code is used. You might find your Diodes at this site:-

http://www.xs4all.nl/~ganswijk/chipdir/n/smd.htm

Here's another cross reference site which starts with the component marking

http://www.dl7avf.info/charts/smdcode/index.html#start

I do not you got answer or not. Here is a piece of advise that I normally adopt. By PWM IC number get data sheet. From data sheet know the switching frequency.(RT&CT) choose diode that can be used at this frequency from diode data sheets.. I am assuming that you know voltage & current ratings of the PSU. You can use two 3 A diodes to 6Amps and so on. you can use 40V diode in place 12V diode.

Dear friend,

i think the PIV rating of the diode will depend on the transformer turns ratio not on out put voltage rating how will he choose a diode only with out put parameters. And he is not aware of transformer turns ratio.

kvsubramanyam :

Thanks for your effort here, but, what is a PWM IC? Do you mean the IC that drives the MOSFET? If so, the PWM IC is a FA5311. I have that data-sheet. I'm looking at it now and among all the other various characteristics, the data-sheet speaks of frequencies in terms of:

Recommended Operating Conditions:

Oscillation frequency - fOSC Min. 5, Max. 600 kHz

Then it speaks of: Oscillator Section: Min Typ Max

Oscillation Frequency RT=5.1kW, CT=360pF 125 135 145 kHz

These 2 photos are of Power Supply. The small black diodes are the ones I need to replace.

Hi, friend

If you are able to probe the switch Gate pulses or across transformer you will get the frequency thus you can select a diode which has more reverse recovery time and voltage and current ratings of the power supply you would be knowing else please give me the PWM controller part number and power supply specs i will try to help you

Every one can not effort for a CRO or Digital Scope meter.

Dear friend,

You are absolutely right, But my intention to suggest that one is he is able to identify some electronic part so i felt that he would be working in electronic related industry.

Okay that should not be a discussion for us

then what would be the best ans that we can suggest him

Thanks for your effort here, but, what is a PWM IC? Do you mean the IC that drives the MOSFET? If so, the PWM IC is a FA5311. I have that data-sheet. I'm looking at it now and among all the other various characteristics, the data-sheet speaks of frequencies in terms of:

Recommended Operating Conditions:

Oscillation frequency - fOSC Min. 5, Max. 600 kHz

Then it speaks of: Oscillator Section: Min Typ Max

Oscillation Frequency RT=5.1kW, CT=360pF 125 135 145 kHz

These 2 photos are of Power Supply. The small black diodes are the ones I need to replace.

__________________
Best, ...Lee.

Yes, I was referring to FA5311(switching regulator). Switching frequency is about 100KHz. So you can use any PC power supply diodes. you can use 1N5822 Schottky diode.

may i know how did you decide the PIV of diode as 40V

to determine the PIV it is must know the turns ratio of the transformer,

There are no inputs given about turns ratio, is there a method to know the PIV without knowing PIV. If yes kindly give me the details

With regards

Suresh

PIV means peak inverse voltage of the diode. PIV of a diode depends on it's silicon wafer processing. That means you can use 100PIV or 600 PIV at 5V no problem. I worked in diode manufacturing. First we used to sort out all above 700V diodes and mark them as 1N4007 then again sort for next PIV range; say 400V and mark them as 1N4004 and so on. Last in the range is 1N4001 which is 100V diode. Normally schotty or normal diodes higher the PIV costly it will be.

This is further to my reply. Long back one customer who was ignorant of this asked us to supply 1N4004. We told them that we can supply 1N4007 but our customer insisted that they require only 1N4004 and also prepared to pay higher price; simply we taken 1N4007 devices and marked them as 1N4004 and supplied them. Both of us ended with happy deal.

Dear friend,

Thanks for your information about PIV of diode.

My intention of asking previous question is in a switch mode power supply any secondary rectifier diodes PIV rating will be selected with the use of Transformer turns ratio only. Not output voltage (5V, 12V) they are not the exact reverse voltages which you diode has to block.

And in SMPS reverse voltage(Which our diode has to block) will be entirely different from the out put voltage

I think the below document would give you an exact view for what i am trying to convey you

Please copy and paste the link shown below in address bar.

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Power%20Electronics/PDF/L-22%28DP%29%28PE%29%20%28%28EE%29NPTEL%29.pdf

Are you saying I can use that 1N5822 anywhere on the board?

can you just mark on the picture posted by you these diode location?

Yes, I can do that and repost the new photos here. Lets get back together sometime this evening. Is that good with you?

You may email me at: lnorman@cablesight.com if you care to. It would make it easier with the attachments.

Best, ...Lee.

Yes, I will mark the photos at the respective diodes that need replacing and repost later this afternoon.

Also, ...if you prefer, you can email me at: lnorman at cablesight dot com .

It might be easier with attachments , etc.

If these diode are as shown in the bottom picture then my suggested diode is not correct. It seems to me that one of the diode is a "zenor" diode. How you decided that they need to be replaced? My advise is remove one side from from PCB and check again. Digital Multimeter will show VF in one direction.

my mail ID: kvsubramanyam@hbl.in

This may not be possible in your circumstances, but, can you just replace the PSU with a cheap PC supply:-

You need to short the power on pin to 0V to turn it on:-

Just a possible suggestion.

I wish. I did think of that in the beginning...but

I have to stay with what I have considering the outgoing wire-harnesses on the right.

It's amazing at times how much information can be conveyed by just a simple picture. In one of the threads, you asked if a Schottky diode could be used for all diodes in this supply. I believe the only honest answer is probably. You must use a Schottky diode for the OFF cycle of the transformer/coil that is switching at 100kHz. My concern though for a diode selection is the voltage reference part. Since you have the data-sheet on the switching regulator, if it has a built in voltage reference then I would feel safe replacing all dead diodes with a Schottky.

My worry though is the diodes found in your lower picture, D10, D11 and the one next to D11. These diodes are a package size that many a Zener diode are found. As you probably know, a Zener diode is the basis for a voltage reference. A Zener diode cannot be replaced by a Schottky diode.

I do question though the value you'll get in trying to repair this supply. At best replacing these diodes will give you a supply that has only a few new parts. The components most likely to fail, the capacitors, have been long used already. In contrast a new supply can be purchased for $48. A review of this supply's data-sheet shows that this footprint appears to be smaller than this elderly unit. So some interface wiring can be done.