How to make a snubber with discrete components

Discussion in 'General Electronics Chat' started by ChrisChemist116, Mar 8, 2010.

  1. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
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    Hello fellow members its me once again:)

    I am trying to build a low cost power supply so in order to accomplish my goal i have been diggin' into my beginner electronics book and there it mentions about snubbing AC. Which it is something i haven't even considered on the first place.:confused:

    So with that idea in mind i went to my local electronics store. But they dont have them.:(

    Looking at the circuit attached, i tried to find an equivalent to a snubber but using discrete components.

    Unfortunatelly i have no idea how to calculate the wattage needed for such resistors and capacitor?.

    Please, i would like someone give me a hand with this?.

    Is it possible to build an RC snubber circuit with discrete components, if so., what would be the values i should choose? .

    I just dont want to get hurt or injured or damage accidentally the components involved.:eek:

    Thanks :)
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    The snubber is used to protect semiconductor switches during inductive switching.
    And also in SMPS
    In ur case at the input of a transformer is typically not necessary, but would not hurt to have.
    A better approach is to use a MOV, Varistor is used to suppress large spikes that sometimes occur during storms and high load switching times. Try to get a MOV with the proper rating on the mains supply that you use and together with a fuse you will have sufficient protection
     
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  3. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
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    Okay i will see if i can get one of those. I believe you're refering to a Metal Oxide Varistor.

    However if i want to introduce or place the snubber at the input of the transformer?. How i do that?. What wattage is needed for the resistor? (Is 100Ohm at 10W okay for 220 volts? )

    I just dont want the resistor blows up when i plug the powersupply.
     
  4. Duane P Wetick

    Active Member

    Apr 23, 2009
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    The transformer input that you show probably does not need a RC snubber across it. If you are blowing that 1 amp fuse. use a slo-blo unit and size it for 200% maximum I rating. For a MOV, a 250 VAC unit with a 40 joule rating (14mm) will be sufficient for most over-voltage events.

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
     
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  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    One of the commonest standard snubbers is 0.1uF plus 100 Ohms.

    You can work out the impedance of the cap at your AC supply frequency, then from that work out the current through the 100 Ohms and therefore the power rating required.

    If it's to be connected to the AC supply, the capacitor should be an X-type, rated for continuous operation on the AC line.
     
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  6. lmartinez

    Active Member

    Mar 8, 2009
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  7. kkazem

    Active Member

    Jul 23, 2009
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    Hi,
    I'm a degreed electrical engineer and a professional power supply designer for over 35 years now. I've designed all types: switching, linear, dc-dc, dc-ac inverters, magnetic amplifiers and more.

    In the circuit shown, since there appears to be a Transient Voltage Suppressor (TVS) on the AC Line side of the transformer, there is no need for a snubber, nor is there a need for an MOV. In fact, the MOV would make the power supply less reliable. Your TVS will do a much better job on input spikes like those caused by lightning. Since your power supply is not a switcher, there is absolutely no need for a snubber. It would be a waste and would do nothing. If you need help in picking out the TVS, I would recommend a 1.5 KW, with a breakdown voltage of at least 375V that's bidirectional.

    Good luck,
    Kamran Kazem
     
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  8. lmartinez

    Active Member

    Mar 8, 2009
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    Interesting Response :rolleyes:
     
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  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    OK buddy. It's time to tell me the difference between a MOV and TVS
    < my mistake>
     
    Last edited: Mar 10, 2010
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  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    Rifaa, this may come as a 'shock' to you: (pun intended)

     
    Last edited: Mar 10, 2010
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  11. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
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    Wow, i can't believe many people answered my post. First of all i want to say thank you to everyone who gave me a hint on how to solve my issue with snubbers.

    It seems kkazem has the expertise? to talk about all kinds of power supply.

    However his response about TVS let me some confused.
    Is there any way that this topic would be a little bit easier for non-experts like me?.

    I hope i am not asking too much for this.

    As far as i understand, in his oppinion there is no need for a snubber as well the MOV. (Is it really that will make the power supply less reliable if it is placed at the input of the transformer?). Because i dont know if there is any way to tell that?

    Are you refering to a transient voltage suppresion diode?, like the ones on this picture? http://upload.wikimedia.org/wikipedia/commons/b/b0/Transils-01.jpeg

    Is their operation simmilar as varistors? i dont know about the theoretical background of them. (TVS)

    It seems interesting, i haven't any idea about their existence. (Sorry maybe i am so beginner).

    Thanks for these documents, they are very useful to me. They dont mention much about the power for use on discrete components, but the theoretical information is very good.

    Yes, at my local electronics store they told me the most common ones were to use an RC network 0.1uf+100 ohms like the ones on this picture http://upload.wikimedia.org/wikipedia/commons/e/ec/Snubber.jpg, unfortunatelly they ran out of them.
    Now i am confused,:confused: which makes the power supply less reliable, a MOV or the TVS?.

    Well i think as far it protects the supply it is fine to me. :rolleyes:
     
  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    I think you missed my post. (you were posting while I was)

    In post #14 you can see that the TVS is the better way to go..

    So you shouldn't need the snubber.
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    So MOV is outdated now....
     
    Last edited: Mar 11, 2010
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Hey retched... what does pun intended mean :confused:
    is it a gesture or expression
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    So MOV's look capacitors and TVS looks diodes, am I right?
     
  16. retched

    AAC Fanatic!

    Dec 5, 2009
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    Rifaa, sorry bro, yes a pun is an expression for a descriptive word used in a meaning that can be taken two ways

    Like: When the circuit worked, I was shocked!

    I was surprised, not electrocuted, but because we are talking about electronics, That would be a 'pun'.

    And TVA is diodes and a MOV looks like a cap. Correct.

    [​IMG]
     
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  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Then I stand by what I said.
    I have seen mov's a lot and it seems I have them both plenty of em' for that matter.
    MOV's are used in supply's to protect them from excessive voltage, where else TVS are used where fast action is needed such as for phone and network equipments.
    Which means MOV does not make a circuit less reliable, it's just that it's not as fast acting as TVS.
    A supply designer or what ever bro, if you don't deal with items at assembly and trouble shooting level as I have been for so long then I guess you don't know what others may use components for, and if you don't personally experiment with such supplies then you never really know do you.

    So retched what was that you was so "puned" ;) about.
     
  18. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
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    Okay thank you, i believe my power supply would be better protected with the TVS in case you are refering to a Transient voltage suppression diodes (transil?) like these ones http://www.mdesemiconductor.com/DIODES.jpg , (will this be good for 220 VAC? http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BZW04-213RL-ND )
    How come has the MOV became outdated?. Is there any particular reason for that?.
    Well i'm just a beginner. :p

    Okay message noted. Although it was not intended to me . :)
     
  19. lmartinez

    Active Member

    Mar 8, 2009
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    I am glad we can be of assistance to you. However, it is not clear to me what you mean by "They dont mention much about the power for use on discrete components." Thank you
     
  20. Bychon

    Member

    Mar 12, 2010
    469
    41
    Please expand "TSV" into whole words so I can look up this device.
     
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