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Power Supply questions

Discussion in 'Power Electronics' started by Ken H, Apr 22, 2014.

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  1. Ken H

    Ken H

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    Dec 22, 2011
    I am specifying a power supply for a new product. What is the difference between a Class A and a Class B power supply? Also, what is special about a "switching Power Supply?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
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    Jan 21, 2010
    Class A and B do not apply to power supplies. There is a lot special about switching power supplies -- it's hard to know where to start.

    Perhaps you can give us some more details on exactly what you're doing and what this power supply is intended to power and we can assist.
     
  3. Ken H

    Ken H

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    Dec 22, 2011
    We are building a personal care product to be used in nursing homes. My device uses a DC gearmotor. I will power this with an 18 V Wall-Plug Power supply. The input voltage needs to be 100/240. The load is 350mA. It shall have a 6 foot DC chord with a DC jack to plug into my device. I have several vendor contacts; that's not a problem. However one of the first questions the vendor asked is: Do you need a Class "A" or a Class "B" power supply? Second question was: Do you need a switching power supply? That is the reason for my posted question.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I think they're asking if you need to be within CISPR Class A or Class B noise limits

    You need to read this, and this.

    Presumably you're aware that your device might be classed as a medical device (when designed for use in such an environment) and are aware of all the additional safety and documentation this will entail?

    Will you need CE mark approval, for example?

    I ask this because my day-to-day work involves medical devices (CE IVD) and we also have to worry about Health Canada, ISO 13485, and other things that probably won't apply to you, but similar things may...
     
  5. Ken H

    Ken H

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    0
    Dec 22, 2011
    Thanks Steve. The text provided indicates the Class A is for a commercial environment while Class B is for a residential environment. That clears it up. The vendors are able to provide UL, CSA, CE, and CCC and are of course RoHS compliant. My company is already ISO 13485 certified, so Health Canada is covered. Interestingly, our device, a specialized power toothbrush, is considered a cosmetic device in USA, but a Class II Medical Device in Canada. Still wondering about that "Switching question"
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    A switching power supply will be lighter, perhaps smaller, more efficient, maybe cheaper in the long run, but it will be more costly to design and certify. Having said that, the psu manufacturer probably has "canned" designs.

    Why not ask them for the pros and cons of each as you likely don't have a requirement either way.
     
  7. BobK

    BobK

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    Jan 5, 2010
    18V at 350mA for a toothbrush? That seems excessive.

    Bob
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009
    hahaha that's what I was thinking

    Dave
     
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