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Transistor regulators?

Discussion in 'Electronic Basics' started by Cruiser, Nov 21, 2003.

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  1. Cruiser

    Cruiser Guest

    I would like to
    know if transistors can be used as a voltage regulator, as with the
    LM317T is for lower voltages. The reason for my question is that I
    would like to build a higher voltage variable regulator .....up to 400
    volts. The older Heathkit types IP-17, and IP-32 used tubes to vary
    the output ( 6L6's ) Up to 150ma @ 400 volts.

    Has this been done using transistors? If so by whom?, Company name?,
    Model?, Schematic?.

    Thanks for any information in advance.
     
  2. Field effect transistors are probably your best bet for this service.
    They are commonly available with voltage ratings up to about 1000, and
    power dissipation ratings high enough to survive a short circuit while
    current limiting, if they are mounted on a large enough heat sink.
    The circuit for them is very similar to that used for tubes, except
    that they require a positive gate bias before they turn on whereas
    tubes are on till you apply a negative bias to turn them off.

    You might look at some of the available devices at:
    http://ec.irf.com/v6/en/US/adirect/ir?cmd=catNavigateFrame
    select Hexfet power MOSFET.
     
  3. John Popelish wrote...
    From a post of mine made a few years ago: ... a simple
    high-voltage regulator that uses standard LM317 or LM317L
    chips plus an easy-to-get reliable high-voltage MOSFET.

    600V FET _____ LM317L 5 to 500V
    IN o----+----, ,-+-----+--| |--+---+----+---o OUT
    | | | | s | | | | | | 2 to 100mA
    | _|_V_|_ | |_adj_| 1.2k | |
    2.2M ----, | | | | | 0.47uF
    1/2 W | '-||--+-----+ | ===
    | | , 68pF | | | 630V
    '--------+---|<|-----------|---' |
    ' 10V zener | 2.7 ohms
    500k |
    pot gnd
    |
    gnd

    The FET needs a very serious heat sink, because 450V at
    100mA is 45 watts, and under a short circuit condition the
    LM317L may allow even more current to flow. You can add
    a single-transistor foldback current limit if you want.

    Add a 1n4002 diode backwards across the LM317 if you plan
    on ever shorting out the input filter-storage capacitor.
    (Always use drain resistors with high-voltage capacitors.
    And always approach the open circuit with one hand behind
    your back.)

    The LM317L needs as much as 2.5mA to operate, and the 1.2k
    resistor only takes 1mA, so this sets a 1.5mA minimum load
    requirement. (Note, you could use 470-ohms instead of 1.2k,
    but this would require a 200k pot with 1W of dissipation,
    instead of the 0.4W maximum dissipated in the 500k pot when
    it's set to about 400k for +400V out.)

    ---

    Note: I haven't tried this circuit, since I prefer to use
    HIP5600 and VB408, etc., high-voltage regulator ICs.

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
  4. Very nice circuit, but you may have to go higher than 1/2 watt for the
    gate pull up resistor to find one rated for the full input supply
    voltage.
     
  5. Lambda made such PSes long ago. So did Dressen-Barnes, LH Research
    and many other companies. I'd guess that most of them ended up on the
    scrap heap. The tube PSes were monster heat generators, so they went
    first. Probably the main reason why they became so unpopular was that
    linear supplies, no matter what the voltage, waste a lot of power as
    heat. Today a power supply with the same output will waste much less
    power and stay cooler, and cost less, with better performance. That's
    because it is a switching power supply, not a linear power supply.

    Go to URL and do a control-F to search for 723, then check the data
    sheet for this IC. You can use it or use several transistors or use
    an opamp for any voltage power supply.
    http://www.ee.latrobe.edu.au/internal/workshop/datasheet.html

    And for god's sake don't get the toob nuts started, you'll never hear
    the end of it! :O)

    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  6. BJT transistors and IGBTs are just as capable as power FETs for this,
    but BJTs are hampered by SOA limitations, so they have to be protected
    against excessive power dissipation. The FETs parallel easily, so can
    handle lotsa power. No matter what kind, your power supply should
    have well designed protection againstg overvoltage and overcurrent.
    If not, then it's not going to last very long. ;-)


    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
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