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Appliance Voltage Usage

  1. Apr 29, 2013 #1
    Hey everyone. I have a question. If we in the US have 110 -120 volts coming out of our house outlets, and we plug in a device that requires 10 or 12 volts... how does it not get fried? Do all devices have some sort of way of stepping the voltage down further to what it needs? Also I noticed that appliances like TV's and computers have more than 1 voltage requirement. For example, some have 1.1,3,3.5,12,and 15 volts? Why is this, does it switch voltages if it's not doing anything? Isn't 3, and 3.5 close enough? Why not just make the requirement 15 instead of all the smaller voltages?

    Thanks!
     
  2. jcsd
  3. Apr 29, 2013 #2

    phinds

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    Why do you think it doesn't.

    Oh ... you probably think that because the DEVICE requires, say 12 volts, that the thing you plug in the wall requires 12 volts. It doesn't. It's called a transformer and it requires 110v in so as to convert it the the 12 volts that the device needs.

    If you plug a 12v device into 110 volts with no transformer then you can bet that it will be fried.

    Yes, here you've got it. They all have transformers. Some have multiple-tap transformers so as to perform multiple step-downs.

    Because many devices, particularly semi-conductor devices, would be fried by 15v.
     
  4. Apr 29, 2013 #3
    Ohh, I completely forgot that a lot of devices have the thick power plug. Now what about appliances that just have a regular size plug and not the big thick power plug? Looking at my can opener, the cable for it, is just the regular sized power cord. How do these convert the 110v ? I don't think a can opener uses 110 volts straight?
     
  5. Apr 30, 2013 #4

    phinds

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    Why do you think it doesn't? a can opener is a motorized device, not a semiconductor device.

    In any event, there can be transformers IN a device --- they don't have to be part of the power plug.
     
  6. Apr 30, 2013 #5
    Some devices use the step down transformer, however most devices now use a process called pulse width modulation. By sending pulses you can control the current as well as the voltage levels. Some can openers can use a DC motor utilizing a PWM circuit.

    here is a straightfoward circuit and covereage of PWM

    http://www.personal.psu.edu/axl17/242l9.pdf

    Their are numerous examples for different voltage/current conversions with PWM. Its also used for VFD's soft starters. Your home PC power supply etc
     
    Last edited: Apr 30, 2013
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