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Thread: DC-DC USB Info

  1. #11
    Variable Bitrate
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    I believe the min is 4V, but I can't find the min current. This is the specs of the switch used: http://www.fairchildsemi.com/ds/NC/NC7SZ384.pdf

  2. #12
    Raw Wave
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    Well.... that's a switch - there is no minimum current for A-B (pins 1 thru 2), it only has a max allowance of 100mA with a 0.5V - 7V range.
    Its On resistance is ~5 Ohms and assume a leakage current of 10uA.


    The Enable (OE; pin 4) must be low (below ~0.5V) for AB to conduct.


    It's what's beyond that switch (A-B; pins 1 & 2) that determines what is required - unless the "Enable" (OE-bar) is the "remote on" etc.

  3. #13
    Variable Bitrate
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    OK, forgive me, but I don't understand any of that except no min current and max voltage. So then the switch pretty much only operates off the voltage? What I'll do is find out what exactly my cigarette lighter is putting out by the end of the week and be back with the info. Thanks.

  4. #14
    Raw Wave
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    I'd say that if that switch was wired to the cig socket, it's now cactus (12V versus 7V max).

    It's intended as a "remote" or whatever from a 5V device - eg, USB supply or PC, not a +12V cig socket.


    But you'd need the circuit diagram etc.

    Or follow its instructions.

  5. #15
    Variable Bitrate
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    It seems they misunderstood what I was asking. They thought I was asking about the voltage for the circuit itself, instead of the remote line. The remote line can take up to 30V. Anyway, it seems that I got a defective unit. The odd thing is that the defective unit works just fine in the house on the bench test power, but once in the car it doesn't work. Then the new unit won't work on the test bench, but works just fine in the car. To make it worse, the new unit won't activate my desktop switch...which works fine if I manually short it...but it will activate the car computer switch. Talk about gremlins!

    Anyway, next issue; I have the led jumpers hooked up to an led. My concern is that this may drain the battery if I don't drive for two days, which happens often enough to be a concern. What can I do to make the led pulse instead of staying on constantly in order to save some power? Pulse maybe once every 10sec or so. Would that help?

  6. #16
    Raw Wave
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    Buy a pulsing LED.

    But LEDs are only 20mA if that.
    Check that you don't have other drains (alarms, remote starts, central locking).

  7. #17
    Variable Bitrate
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    Are you saying 20ma isn't enough to drain the battery over two days? Buying a different led isn't really an option right now.

  8. #18
    Raw Wave
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    That's right.
    Many consider up to 50mA is ok (for alarms etc).

    The common Bosch alternators I once used draw 12mA.

    I left my dome light on overnight on the snow and she still cranked the next morning. The dome was probably 10W else 5W (hence ~480mA or 240mA).



    You said this "is a concern".
    Try it and see.

    Or measure your existing drain so you have something to compare with.

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