pwm power control

Discussion in 'The Projects Forum' started by quioui, May 27, 2012.

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  1. quioui

    Thread Starter New Member

    May 27, 2012

    I am trying to control the power delivered to a 100W lamp by pwm. First I rectify the AC signal by a full wave rectifier, then I use a power mosfet for pwm'ing the power, as in figure.

    I am using a switching mode power supply that has its own GND, which is GND2 in the figure. The problem is when I connect the ground of the rectifier(GND1 in figure) with the ground of the power supply(GND2) I get 220V everywhere. I got electrocuted from the metal casing of the power supply. I just can't see what is the problem here, what do you think?


    Thank you.
    Last edited: May 27, 2012
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
    When I click on your link it asks for my yahoo password. Seems legit, and IIRC flikr & yahoo are linked, but I'm not taking any chances. Post your circuit here, using attachments.
    quioui likes this.
  3. crutschow


    Mar 14, 2008
    Good grief lad, are you trying to kill yourself? :eek:

    You never connect directly to the mains power for the very reason you discovered. The diode bridge does not isolate you from the mains voltage and thus you get 220v from your bridge ground connection to the circuit ground.

    You must use an isolation transformer to isolate the mains power from your circuit.
  4. hgmjr

    Retired Moderator

    Jan 28, 2005
    I have locked this thread as it violates our Terms of Service against transformerless off-line designs.

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