Reducing DC voltage

Discussion in 'DIY Discussion' started by locky, Feb 3, 2006.

  1. locky

    locky

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    Hi There,
    I'm about to start another project - this time a 300W D-class amp from 41hz. I have located a SMPS which will give me 48vdc and the required wattage but I also need a 5 volt regulated supply for part of the circuit. What's the standard way of taking the 48vdc to about 9vdc? It will then pass through a 5 v regulator with the appropriate caps etc... On the last project I took a seperate ac/dc tX from the 240vac and rectified and regulated it, but this time I would rather take it rom the dc out of the SMPS so that it starts up at the same time.
    Any advice appreciated...
     
    locky, Feb 3, 2006
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  2. locky

    felix part-time Horta

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    How much currentdo you need? Dropping 40v means you're going to dissipate quite a lot of heat... 40V is also too much differential to use an LM317 or similar.

    One good way would be to use'd look at using a zener on the base of an emitter-follower (transistor) on a heatsink. This would also provide quite a lot of noise/ripple filtering before the local reg, no bad thing at all.

    EDIT: see the 'zener + follower' section on this page: http://www.tnt-audio.com/clinica/regulators_noise3_e.html
     
    Last edited by a moderator: Feb 3, 2006
    felix, Feb 3, 2006
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  3. locky

    spev

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    I've got a similar setup inside my amp here - +-40V dc reduced to +-16V by a zener setup, which then goes through a basic 317/337 to give me +-10V out the other side.

    Got to be careful your zener resistor can supply enough current for whatever regulation/load you have after it
     
    spev, Feb 3, 2006
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  4. locky

    zanash

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    Might just be simpler to add another transformer and rectify to your desired voltage.
     
    zanash, Feb 3, 2006
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  5. locky

    locky

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    You may be right. My only concern is whether they will be a problem with the 5v supply starting up at a different time to the 40vdc from the SMPS. As far as I can see the 5v supply is for the section of the amp that converts the analog into digital before it reaches the Tripath chip. It is the AMp 2 from www.41hz.com
     
    locky, Feb 3, 2006
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