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Need help with design

Discussion in 'Power Electronics' started by Y2KEDDIE, Jul 25, 2019.

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    Sep 23, 2012
    Experimenting with "vintage" radio circuits I find myself in need of various high voltage supplies,typically in the range of 250 to 650 VDC.

    I have several industrial type transformers designed to boost 120 to 220 VAC and, 220-440 VAC, at several amps. These were used for running light , lighting and small single phase motors from a 3 phase motor control center. Physically they are 6X6X8" in size. I have quite a few.

    I've been able to build unregulated supplies by wiring the primaries in series and secondaries in parallel combination. Resulting in 120V input, 220/440/880 output. With rectification and filtering I can get (1.414X) : 311 ,622, and 1244 VDC unregulated at several amperes.

    What I would like to build is a series pass element regulator circuit to yield: 100V, 250-275, 350-375.400-775, etc, variable output at 0.5 to 1 ampere.

    I found a circuit using a Supertex LR8 High Input Voltage Adjustable # terminal Linear Regulator and a TK9J90E MOSFET as a pass element. I'm not sure if these parts are still obtainable (obsolete), but I need something , if not similar.

    With 311,622,1244 VDC fixed, a lot of voltage drop would be needed to occur requiring a lot of heat sinking. Never the less my quest, if practical, is to find a circuit to accomplish this.

    Has anyone else tried this? Are there more practical components /circuit designs available?

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Sure? Not primaries in parallel and secondaries in series?
  3. duke37


    Jan 9, 2011
    At 1A you will be dissipating a lot of heat even with a small voltage drop.
    Consider using an appropriate transformer tap to minimise the drop.
    Chose a lowish voltage supply and then use a switch mode boost circuit to get the higher voltages.
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    You can use a variable autotransformer on the primary side to adjust the primary voltage and thus the secondary voltage. This method incurs rather small losses.


    Sep 23, 2012
    My bad, I meant primaries in parallel, secondary in series.

    Yes, I could buy a tapped transformer with the exact voltages, but I want to use what I have.

    Yes, I’ve used Auto transformers (power-stat) in a single voltage supplies. My goal is to build a multi voltage supplies. One particular supply example: I need [email protected] mA regulated, [email protected] regulated, and [email protected] mA un regulated. I would like to use two 120: 440 transformers, which I have in my stock.

    Switch mode would work, but again: I wish to use the transformers I have in stock, and keep it linear.

    With the secondaries in series I can get the 800V-1200v. I can use one secondary as a tap for the 110 and 275v, but I need to drop the voltage/regulate.

    A simpler way to approach this: how can I get 110 v and 275 v regulated from a 622vdc supply?

    The goal is a circuit similar to a low voltage supply where they use a single transformer /rectifier supply with multiple solid state regulators to achieve multiple voltages.
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