28volts power supply

Discussion in 'The Projects Forum' started by samrat, Aug 26, 2008.

  1. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    Just asking for help if a circuit diagram of a 28 vdc/4A with 240v input can be given to help my group with our major project. This power supply is needed for our 50 watts of rf power amplifier. We do need a diagram with readily available components. :confused::confused:
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    For a RF transmitter I would go for a schematic with an ua723.
    This IC is reasenable rf tight.
    The schematic in the link is maybe a bit overdone, but gives a good impression.

    Part 1 : http://www.uoguelph.ca/~antoon/circ/ps3010/ps3010a.html
    Part 2 : http://www.uoguelph.ca/~antoon/circ/ps3010/ps3010b.html
    Part 3 : http://www.uoguelph.ca/~antoon/circ/ps3010/ps3010c.html
    Part 4 : http://www.uoguelph.ca/~antoon/circ/ps3010/ps3010d.html

    You could also look for special switching regulators suitable for RF.

    Greetings,
    Bertus
     
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
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  4. bertus

    Administrator

    Apr 5, 2008
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    Hello Studiot,

    Is the LM338 suitable for RF applications?
    For RF applications, specialy power amplfiers you should take care that the RF signal does not influence the powersupply voltage.

    Greetings,
    Bertus
     
  5. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Bertus, you have me curious, how does the rf influence the regulator?
    I've never run into that problem, but if I do, it'll be a huge help in finding out what is going on.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    hello,

    When the RF signal gets to the regulation circuit, it can raise or lower the output voltage.
    In my job we use the ua723 in the regulators for the transmitters.
    These transmitters can produce 200 Watt peak power.
    This can be solved by putting inductors and capacitors as filters on the output. (see the schematic in my first post).

    Greetings,
    Bertus
     
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Many RF amplifiers, power and otherwise, use tuned circuits. In particular they use inductive loads.

    Inductive loads can give rise to inductive 'backswing' voltages and other effects.

    Are you referring to this?

    I agree that extra filtering may be required, including the possibility of cascaded regulators, perhaps with a series choke to take care of any RF problems.

    Good point Bertus.
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The schematic with an ua723 looks a bit "oldfashioned", but it is a good circuit for a RF stable powersupply.
    The chokes on the output are there to keep the RF away.
    Also build it into a steel cabinet, to shield it from the RF.

    Greetings,
    Bertus
     
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