DC power supply without transformer

Discussion in 'General Electronics Chat' started by Peter Pan, Feb 19, 2009.

  1. Peter Pan

    Thread Starter Senior Member

    Mar 24, 2005
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    Hi,

    I am interested whether it's safe to use home made DC power supply which does not have a transformer. This supply consists of rectifier and simple filter (to smooth voltage pulsations) only and can be connected to 230V AC mains (which is its input) and provides about 200V DC output.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    It is never safe without a transformer.
    The transformer gives isolation from the mains.

    Greetings,
    Bertus
     
  3. b.shahvir

    Active Member

    Jan 6, 2009
    444
    0
    DC power supplies without transformers are available (actually they contain small HF Xmer but it does not provide electrical isolation) and are used in modern electronic appliances like computers & TV sets. They are widely known as 'Switched Mode Power Supplies' (SMPS).

    However, they should never be opened with power ON as the chassis of SMPS unit carries line voltage (120VAC or 220VAC) depending on rating and can deliver nasty electrical shocks if tempered to with mains on.
     
  4. Peter Pan

    Thread Starter Senior Member

    Mar 24, 2005
    122
    0
    Hi Bertus,

    Thank you. This power supply is supposed to be used with the 60 Watts linear RF amplifier using IRF840 which we talked about on the week - I wonder how much current it will need if it is supposed to be powered by DC voltage about 100-120V? I will need to figure out what transformer to look for.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When you look at the site it says 700 mA @ 60 Volts.


    Greetings,
    Bertus
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    What type of amplifier is it? class A, AB, B?

    What is its efficiency?
     
  7. Peter Pan

    Thread Starter Senior Member

    Mar 24, 2005
    122
    0
    Whether it's possible that an amplifier which takes 42W DC (P=I*U, so here P=0.7A*60V=42W) from power supply will amplify a signal to 60W?
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    You are right.
    I think you should take 125 Watts for the powersupply, if you want 60 watts output.
    (I think you can sometimes have your doubts about what they write on the net).

    Greetings,
    Bertus
     
  9. Peter Pan

    Thread Starter Senior Member

    Mar 24, 2005
    122
    0
    Agh, that was not actually wrong (just an understatement) when they say that "The circuit draws 700 ma at 60 Volt Vcc" as then author says that "my IRF840 power amplifier working at 120Volts". But one who wants to construct the amplifier has to think for himself.
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    Yes, those things happen, some misreading.
    Take care of cooling the FET well. (it has to dissipate some watts).

    Succes,
    Bertus
     
  11. Peter Pan

    Thread Starter Senior Member

    Mar 24, 2005
    122
    0
    It's about an amplifier described in the file attached. I am not absolutely sure what its class and efficiency are. :rolleyes:
     
  12. Peter Pan

    Thread Starter Senior Member

    Mar 24, 2005
    122
    0
    There will be big enough radiator (maybe even fan). Thanks for advising this design - LTspice shows that it works nicely!:)
     
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