Trying to find this diode's datasheet ( PR 73A)

Discussion in 'General Electronics Chat' started by LETITROLL, Sep 1, 2015.

  1. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Hello everyone .

    I am now trying to find a replacement for a diode that is shorted .

    This diode is in parallel with a smps transformer main primary input.

    I don't really know what type is it .

    The psu input is from 80 V ac to 230 V ac.

    Any ideas .


    Here is a picture of the diode that i uploaded. ( the other hole is behind the yellow component)

    [​IMG]
     
    Last edited: Sep 1, 2015
  2. wayneh

    Expert

    Sep 9, 2010
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    So you removed the diode before determining it was shorted? In parallel to a transformer, it would appear shorted on the PCB.

    Is your diode in the picture? I don't see it. A 73A diode would be much larger.
     
  3. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    I of course removed it and it was shorted displaying 0.4 ohms both ways .

    The diode is just near the yellow component , you can see the SMD solder pads.

    Here is a picture of it befor removal :

    [​IMG]
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    The 2SK2884 is rated 800V, so the diode probably needs to be at least that, hard to judge the scale but I'd say at least 1A - maybe as much as 3A.

    Pretty sure it'll be a fast-soft recovery type.
     
  5. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Thanks ian a lot.
     
  6. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    What interesting in this PSU , is that it doesn't have an oscillator apparently only a power factor corrector , and a tl431 at the output for charge monitoring i guess .
    Could the power factor corrector be also doing the job of an oscillator ? the part is L6561D.
     
  7. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    How do you know that it actually was a diode? Could be a transil for example.
     
  8. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Do you mean transient voltage suppressor ?
    I searched for the logo name and it belongs to general semi , but still cannot find a datasheet for it.
     
  9. kubeek

    AAC Fanatic!

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  10. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Thanks kubeek , i already looked at it , sadly there is nothing about 73A , i don't know the exact ratings.

    But anyways is it safe to power the PSU without it ?
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    That is hard to tell, are you planning to put that transformer back in? I would imagine the 73A is some marking of manufacturing week or factory or combination there of. You might try asking the manufacturer directly.
     
  12. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Couldn't have done better .

    Thanks for your time anyways.
     
  13. ian field

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    Oct 27, 2012
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    Apparently you can also get resistors disguised with SMD semiconductor codes - but in one of the pictures, the part in question has a polarity bar on the case which seems unlikely. Also a resistor would be bigger than that in a snubber - and there are some the right size nearby.
     
  14. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    As a little update : i have powered the PSU without the diode in place and there is no output.

    Just to mention that this psu has a tl431 at the output , aniyone knows what it role in that design , because i may be thinking of replacing the whole PSU with another one even from a laptop or something else.
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
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    The TL431 is a "programmable zener", you can simplify its internal function as a comparator with a built in 2.5V reference.

    If you put a 2 resistor divider from cathode to anode and the tap to Vin - you can increase the cathode until the voltage at the tap reaches 2.5V - then it will start to conduct from cathode to anode just like a zener diode. If you connect Vin directly to cathode - you have a 2.5V zener.

    In most applications a comparator earns its keep by switching hard on or hard off, in the TL431, its usual application is within a negative feedback loop which keeps the comparator constantly balanced on its linear region.
     
  16. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Tl431 is usually used to drive the feedback optocoupler to maintain output voltage.
     
  17. ian field

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    You could do just the same with an actual zener diode - and a few manufacturers of lower spec units sometimes do.

    The big deal with the TL431 is that its adjustable or "programmable" - you can feed the Vin pin with a pre set pot to set the output voltage just so. For high spec or critical regulation; you usually find 5 band 1% resistors and holes in the board for additional select on test resistors. Pots can get noisy as they get old.
     
  18. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    OK , i previously thought that this tl431 is having something with the battery charger.

    I forgot to mention that before this PSU failed , the spectrum analyser was turning on , but the battery level indicator was showing a "?" symbol , i was still troubleshooting that particular problem before jumping to my actual situation.

    So since i have a 9.6 V at 4 Ah battery pack , can i use any psu within that range , the PSU by the way was outputting a clean 10 volts DC , also what wattage should i go with ?
     
  19. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Sorry for insisting a bit .

    I am going to buy a new PSU as a replacement for the battery charger , but i need to know what is the current rating for safely charging the 9.6 v battery pack ( 6 cells lithium ion) , they are also rated at 3800 Mah.
     
  20. ian field

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    Oct 27, 2012
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    In almost every case, using a PSU to charge batteries is a bad idea.

    Charging lithium packs with anything other than a charger designed for the job is positively dangerous!
     
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