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relating to transformers

hell all,

we are designing a small transient detector as a student project ....can we get a transformer which can step down a high frequency transients as well as 50/60Hz ac signal simultaneously by the same factor....?

if transformer is not suitable ,which is the best attenuater which should be used in this  kind of situation??.....atteneuator is must as we cant deal with high  120V/230V signals...........

6 Replies

  • Manojk,

    I'm not sure what type of bandwidth you are seeking.

    Though transformers intended for transferring power are not designed for wide bandwidth, some small ones may do pretty well. Try some transformers in "wall warts." Not the newer ones with high frequency switching supplies, the old ones with only a transformer, rectifier and capacitor. You can tell the difference because these old simple ones feel heavier. Some of these types have an AC output (no rectifier or filter internally) so you would not need to take them apart to get directly to the output of the transformer.

    My guess is that ones designed for the smallest power output are likely to have the best bandwidth.

    Though you could make a passive attenuator with resistors, I don't recommend it. It is far safer to use a transformer which provides galvanic isolation between the line and your measurement circuitry.

    Regards, Bruce.

  • In reply to Bruce Trump:

    thanks for your kind reply sir ........we are interested in the voltage swell ,sag and voltage transients occurring in a power line.

    but the problem is we cant really predict the nature of transient and the rise time of the transients are too low that no transformer can be fitted for that ......so please suggest us the best way of implementing it..........

    thanking in advance,

    MANOJ

  • In reply to manojk peradka:

    Manoj,

    A transformer of the type I described will provide a lower voltage replica of the input voltage that is galvanically isolated. I suggest that you start with this approach. You will be able to safely analyze the voltage variations and transients. You can test the bandwidth of the transformer.

    Regards, Bruce.

  • In reply to Bruce Trump:

    thank you very much sir....i ll do as you said......also, will defiantly approach in case if i get any doubt....... 

  • In reply to manojk peradka:

    an other question is there.........can we use photo transistors to couple mains to our required level instead of a transformer........????will transients get coupled efficiently if we use it??   is the bandwidth of photo transistors is greater compared to the transformers???????

  • In reply to manojk peradka:

    Manoj,

    Optical couplers can potentially provide wider bandwidth but they require special circuitry to provide accurate linear response over a bipolar voltage range. Other possible techniques for galvanic isolation include isolation amplifiers such as the ISO124 or AMC1200. These devices require a power source on the input isolated side.

    I suggest that you start with the transformer approach I suggested. Measure its performance before attempting something more complex.

    Regards, Bruce.