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    AC to AC step down converter circuit 110V AC to 40V AC, not a transformer

    Hello,

    Aside from using a transformer, how could I supply my circuit with 40V AC [500mA (12VA) or more] given a standard 110V AC (standard wall power)?

    My goal is to make a self-contained project box that houses its own power supply circuit rather than using a bulky transformer.

    Any key terms to search against or part numbers or URL references [minus google.com :)] would be greatly apprecieated.

    Thanks,
    Moe

    •   Alt3rd October 2012, 19:19

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    Re: AC to AC step down converter circuit 110V AC to 40V AC, not a transformer

    If you need DC then you can use a line operated switching regulator which can be made quite small.

    For AC you will need to use a standard bulky transformer.
    Zapper
    Curmudgeon Elektroniker



    •   Alt3rd October 2012, 20:22

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    Re: AC to AC step down converter circuit 110V AC to 40V AC, not a transformer

    Here are a couple of theoretical alternatives to a transformer, since you ask...

    Your specs imply a load of 80 ohms. You want to drop mains AC to about 1/3 its voltage.

    If this load is constant then you can install a 600mH coil inline with the mains AC. This particular henry value will create 160 ohms of impedance at 60 Hz. The coil will be about the same size as a transformer. It must handle 700mA peak (56 W).

    Or theoretically you can install an 11.6 uF capacitor inline. That is the value that creates 160 ohms of impedance at 60 Hz. It is risky to reduce mains AC by capacitive drop, which is why you won't see it recommended for more than small current needs (such as an LED). You are asking for 700 mA peak.

    A bulky transformer remains the most reliable method.



    •   Alt3rd October 2012, 21:50

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    Re: AC to AC step down converter circuit 110V AC to 40V AC, not a transformer

    Actually, I can supply my project box with 40VDC, so I am guessing they make a 110V AC to 40V DC converters? What would I search for if I need such a thing?

    Thanks,
    Moe
    Last edited by average_male; 4th October 2012 at 00:49.



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    Re: AC to AC step down converter circuit 110V AC to 40V AC, not a transformer

    40V is higher than the everyday range of DC adapters.

    If you want to include the power supply in your project enclosure, there's always the idea of making your own.

    The easy type is a full-wave bridge supply. It uses a transformer, full-wave bridge rectifier, and smoothing capacitor. A fuse is a good idea. And a switch if you need one.

    The transformer can be between 35 and 40 V. Rated to provide 500mA (or up to 1A to provide a cushion). By using a transformer you are isolated from mains AC.

    Diodes should be 100V reverse rating. 1 A (or 3A for a cushion).

    The smoothing capacitor can be 1000 uF to 2200 uF. It depends on how much ripple you can tolerate.

    A switched-coil supply is another option (as Crutschow stated). It will be harder to design and construct one. You won't have isolation from mains AC, unless you use a flyback which contains a transformer.



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