100v to 12v

Discussion in 'The Projects Forum' started by Freedomphyta, Oct 17, 2011.

  1. Freedomphyta

    Thread Starter New Member

    Jan 29, 2011
    2
    0
    Dear Community

    I am trying to get 12 volts (dc) from a 100 volts (dc) supply. I initially employed a 67D-48S12R to get 12 volts from 70 volts but the latter is no longer available to me and I have to make do with a 100 volt supply. does anyone know any equivalent to the 67D-48S12R or any other way to do this. Series or linear regulators. Thank you

    Freedomphyta
     
  2. mcasale

    Member

    Jul 18, 2011
    210
    12
    From a quick Google search, it looks like there are still suppliers of the 67D-48S12R. Was it the 70VDC that went away? How much current does your 12V load draw? Is this for a product for sale? I THINK there are AC-DC converters that also accept DC input, but I have never done this myself. They usually rectify the incoming AC anyway. Perhaps someone else has more experience with DC input to an "off-line switcher".
     
  3. Freedomphyta

    Thread Starter New Member

    Jan 29, 2011
    2
    0
    @mcasale, thank you for your reply. It is not for a product for sale. It's part of my final year project. It's an automatic home alarm system running at 12 v. It is very easy to buy a 12 v battery and get it done and over with but my supervisor wants me to charge the battery from a 72 vdc UPS battery system in the house. This is to ensure the alarm is on at all times even when the ups is dead. I designed it using a 70vdc power supply forgetting that when the UPS batteries are charging, the voltage goes as high as 100v and this can damage the chip(67D-48S12R) as it only works 36-72v input. now I need a way to convert 100-50vdc to 12 vdc.
     
  4. mcasale

    Member

    Jul 18, 2011
    210
    12
    OK, I understand the application a bit better, but how much current is drawn by the 12V load - both the battery charger and the alarm system?

    As this is not for a product, you could try clamping the input to 70 volts using a power transistor and perhaps a zener diode for a reference. This is a brute force approach. If your load is just a few milliamps, the power dissipation in the transistor won't be too bad, but it is very important.

    Another approach is to chop the incoming DC voltage and then run it through a step-down transformer and rectify and filter it.

    The best approach depends on your load and how much money you want to throw at it.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you don't mind building your own, the LTC3703 might be used:
    http://www.linear.com/product/LTC3703
    The specs for the original supply were 15 Watts, so for a 12v output that would be 1.25A.
     
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