Connect with us

Not so easy led driving.

Discussion in 'Electronic Design' started by Fred Bartoli, Mar 29, 2007.

Scroll to continue with content
  1. Fred Bartoli

    Fred Bartoli Guest

    I've a situation where a string of 5 Leds (2mA) has to be powered from
    48V up to 1kV (HV safety indicators). That's about 20mW for the leds,
    and 2W heat under 1kV.

    The system ATM is a simple CC source (1BJT + 2 mosfets) but we now need
    as less heat generation as possible and a more compact design.

    The first idea was a resistive drop down to 50V or so, and from there
    have a small step down switcher current regulator providing the 2mA current.
    At 50% efficiency that would have been 0.8mA for 1.2W saving, and
    possibly more.

    ....but all the little switchers I could find either have huge current
    draw or low max input voltage, or something.

    Before I start rolling my own, which seems not so simple (first attempts
    show a serious lack of 'efficiency')
    I have to ask if I missed the good IC? (or idea)
  2. anything here

  3. colin

    colin Guest

    "Fred Bartoli"
    how about more leds in series using less current for the same light output ?

    Colin =^.^=
  4. Fred Bartoli

    Fred Bartoli Guest

    colin a écrit :
    One Led is also an opto (visual feed back for the operator and to the
    calculator too).
    And all that is doubled for redundancy :-(
  5. Fred Bartoli

    Fred Bartoli Guest

  6. James Arthur

    James Arthur Guest

    Must you power the LEDs from the 48-1kV? If not, you could make an
    isolated supply to power the LEDs, and a separate circuit to sense the
    high voltage: (warning: crude sketch)

    +15v (isolated)
    +HV >------. +--+--+
    | | |
    | | LED1
    R1 | | :
    | | LEDn
    +---------|\ |
    | | >----'
    R2 Vref >-|/
    | |

    The isolated supply could be very simple, and unregulated.

    That would solve the heat problem, and could also be smaller than
    the space otherwise needed to dissipate 1-or-2 watts.

    James Arthur
  7. Terry Given

    Terry Given Guest

    or just a self-oscillating flyback converter driving the LED, using a
    suitably high voltage device. just let it clag out naturally when Vin
    gets low enough.

    I built a 1W 100V - 1kVdc flyback with an emitter switched BU508 once.
    and it was harder to do than the 100W version.

  8. joseph2k

    joseph2k Guest

    maybe buy one of these?
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day