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A non-traditional use of LM431

Discussion in 'Electronic Design' started by Vladimir Vassilevsky, Oct 23, 2007.

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  1. Joerg

    Joerg Guest

    No pun intended but didn't you just reinvent the concept of the 4-20mA loop?
  2. It is not about the concept, it is about the schematics. This circuit
    was initially designed for factory programming of the sealed wireless
    sensor. After the programming is done, the battery is connected to the
    power terminals. There is no additional drop on the power rails.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
  3. Jim Stewart

    Jim Stewart Guest

    Somewhat reminiscent of a design I did many years
    ago. I needed to power and communicate with wellhead
    controllers over 3 miles away over a single twisted
    pair. I used a constant current 50ma source in
    series with a 600 ohm telco transformer on the local
    side and a 5.1 volt zener in series with a 600 ohm
    tranformer on the remote side.

    I took 25ma off of the 5.1 volt zener to run the
    remote and used 300 baud single-chip modems on the
    transformers to send and receive data.
  4. You almost (re?) invented HART protocol, but 300 rather than 1200

    Best regards,
    Spehro Pefhany
  5. Jamie

    Jamie Guest

    Or though a good idea, it isn't new. sorry.

    Maybe the way you're implementing it with the
    arrangement of components maybe but the net results
    is still the same.

    for example:

    We modified some equipment that operates a DC
    magnetic tension clutch supplied via a set of slip rings (collector
    rings) to energize the coil on the spinning mast.

    We needed a way to detect if the clutch was locked or slipping
    with the driving mast. So, we mounted a prox sensor on the mast just
    behind the clutch disc where it has timing teeth which was used for the
    prox sensor. I used the DC that's supplied the clutch and
    past it through our current amplifier that was mounted on the mast. this
    voltage also served as a voltage supply to operate the prox via a
    regulator. Any ways, the circuit simply varies the current slightly that
    represents the proximity sensor activity.
    At the supply end on the other side of the slip rings, one leg is
    past through a 1:1 xformer which isolates the raw DC (0..90V DC) and
    gives us the pulsed signal we used to determine if the clutch is in slip
    or locked rotor.

    You need a clean DC power supply to operate the clutch other wise,
    you'll get noise in the detector circuit..
    The other method would be sending burst of 50khz for each prox pulse
    which I did on one. It's all about cost, clean power supply verses using
    a dirty one with high freq pass detection.
  6. Winfield

    Winfield Guest

    Is that a real circuit, or just a spice-model circuit?
    The LM431 has a rather high voltage gain. It also has
    a DC voltage tolerance, up to 50mV, or 2%. I noticed
    the LM431 amplifier in your circuit is biased without
    any dc feedback, from two 33k resistors (5% resistors)
    dividing the 5 volts (5% is a common tolerance for 5V,
    where does the 5V come from anyway?).

    I wonder if in real life some fraction of LM431s might
    not be saturated ON or OFF from the random accumulation
    of voltage tolerances in the circuit, especially as a
    function of the applied 5 volts?
  7. Robert Baer

    Robert Baer Guest

    Please do not give references to nasty URLs like above; it is so
    browser hostile that i had to use power-off reset to regain use of my PC.
  8. Jim Thompson

    Jim Thompson Guest

    It's a Larkin-style circuit... you just have to "tap tap tap" it just
    right ;-)

    ...Jim Thompson
  9. It works either way. You can try soldering iron or spice.
    It has been accounted for.
    Is it a problem?
    The current flows through R1, the whole receiver circuit operates as the
    voltage source. The voltage across R1 is proportional to the input current.

    , from two 33k resistors (5% resistors)
    Look at the schematics.
    Applied is the current, not voltage.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
  10. Joerg

    Joerg Guest

    Oops, may be time for a nwew PC ... or at least a new browser. Works
    fine here. It's a regular htm file on his company's web server or provider.
  11. Jim Thompson

    Jim Thompson Guest

    Works fine here also. But I normally run Firefox with severely
    throttled script capability.

    ...Jim Thompson
  12. Joerg

    Joerg Guest

    Same here. Enjoying the new PC now. Someone suggested I should plunk
    down some more dough and get the Intel dual-core. So I did and also
    upped to 2Gb of RAM. Had to do some Spice today. Man, this thing rocks
    and the fans didn't even speed up.
  13. I'm enjoying my quad core. ;-)

    Best regards,
    Spehro Pefhany
  14. I write this from 150MHz/64M Pentium-I Win98/IE6 machine. No problems with
    I think Robert Baer needs to reinstall the driver skilfulhands.sys.

    Vladimir Vassilevsky
    DSP and Mixed Signal Consultant
  15. Winfield

    Winfield Guest

    Is that made clear?
  16. Joerg

    Joerg Guest

    Spehro, you just had to say that, did ya?
    I used such a machine until a couple weeks ago. Worked fine for Usenet
    and Gerber check but then it let off a few suspicious hisses and needed
    several PS start attempts on some days.

    Maybe it's a browser config issue. Your link was one of the faster
    loading ones, no problems here.
  17. Joerg wrote:

    I keep this ~12 year old workhorse. It is handy to have the ISA bus and
    the direct access to the true LPT/COM ports on occasion. Everything
    works fine, but all video applications are immediately out of class,
    opening PDF files is a torture, web pages are loaded much faster then
    If you don't mind the dirt and dust, there are the biasing resistors at
    the power transistors in the PS. Reduce those resistors to ~100k value.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
  18. Joerg

    Joerg Guest

    I know, I could kludge it. But there were also some pop and crackle
    noises on occasion, not so good...
  19. Robert Baer

    Robert Baer Guest

    I bet the reason "it works" is because you are using IE.
    It cannot be "a regular HTML file" and do that; perhaps there is a
    lot of Java or related fiddling going on.
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