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265V PS Needed For Braille Display

Posted by Cliff on from the obscure-voltages dept.

Harald Klein writes: "We are developing a cheap braille display for visually impaired people. A big problem is the power supply for the piezo elements. They need 265V DC, 0.5 mA max. The logic needs 5V DC, 15 mA. It is absolutely necessary to provide logic power before providing the high voltage. Even so the high voltage should be removed before logic power and signals. Any power supplies in mind that meet the specs?"

4 of 10 comments (clear)

  1. Power supply design by Anonymous Coward · · Score: 3

    Shouldn't be too hard to make one. Start with a 5V supply capable of giving 1A or so. Have a delayed signal from the "logic voltage" start up a 50Hz (or so) sine wave oscillator (simple 555 circuit + small IC-based audio power amp would do), feeding a mains transformer in reverse. Put the output from the transformer through a suitably-rated full-wave bridge rectifier and smoothing circuit. The input to the transformer will have to be capable of driving at least 0.5*265/x mA, where x is the rms voltage output of the amp.

    You'll have to work out the conversion factors to ensure you can get to 265V output based on oscillator amplitude (make it adjustable), transformer ratio (depends what mains voltage the "primary" (which you are using as a secondary!) is designed for), rectifier ratios and losses. You might need to start with more than 5V to be able to get up there: say 15V perhaps?

    BE CAREFUL: despite the low current capability, 265V can do you serious harm.

    ac.uk

  2. Piezos do braille ?? by blakestah · · Score: 2

    How are you going to get the necessary 0.5 mm of amplitude from a piezo element ??

    It seems you would have to leverage it up with a lever ratio of at least 5.

    In any case, the piezo will draw very little current. I'll check on our power supplies in a few hours when I hit work. We use piezos for somatosensory stimulators (at about 100 microns of amplitude).

    1. Re:Piezos do braille ?? by dingbat_hp · · Score: 2

      I used to work with lasers, where long-throw piezos were commonplace as mirror adjusters etc.

      Some use levers, but that's awkward to make and less accurate in use. Maybe they'd work for this, where it's a fairly simple "up or down" output.

      The usual method was to stack piezos, so that they were mechanically in series, but electrically in parallel. This gave you long throws (a few mm), but with voltages in the hundreds of V, not the thousands.

  3. Not too difficult... by stienman · · Score: 2

    You aren't going to find a pre-built unit for this, your best bet is to find someone who knows what they are doing to build one for you.

    Assuming you are going to be getting you main power from the AC line, get a low-amperage step-up transformer. It will convert your 120VAC to 240VAC. Using a rectifier and filtering will get you about 300VDC at no load. If you load it correctly you'll end up with about 260-270 VDC, which should be well within spec for your piezo elements.

    If you need this to be battery operated, or you need the above to be exactly 265VDC, then you need to get into switching power supplies. At that point, unless you know what you are doing, you should get someone else to design it for you. High voltage power supplies are something of an art, since insulators don't act like you expect them to. It's kindof like trying to charm rattlesnakes...

    -Adam

    All power corrupts - but we need electricity!