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5 volt power supply

Discussion in 'General Technical Questions and Answers' started by KD7FQI, Aug 1, 2020 at 9:22 PM.

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  1. KD7FQI

    KD7FQI Ham Member QRZ Page

    I am look for a high quality, RF quiet, 5 volt, around 10 amp power supply. I prefer linear supplies over switchers. I am trying to replace seven USB wall wart adapters that are making some noise on 160 and 80 meters.

    I am open to building something but want to watch the cost of the whole project.
    PU2OZT likes this.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    A 6.3Vrms center-tap transformer rated 10A with a full-wave center-tap rectifier (two diodes) and a 1000uF 15WVDC filter capacitor would make a decent design that would provide about 4.5Vdc at full load and probably more like 5Vdc under light loading, which is all you'd likely have.

    Although USB is rated 5V @ 2A, very few USB appliances actually draw 2A; cell phone and tablet internal charging systems for example are usually in the 1A each range, or less.

    You could go fancier and make it regulated by not using the center tap and instead using a full-wave bridge rectifier which would provide about 9Vdc into a linear regulator to provide 5Vdc constantly with or without a load; that would add only a few dollars to the design but probably require a heatsink for the regulator.

    30-min project. Might look to find a deal on the transformer by looking at surplus houses like Fair Radio et al.
  3. W1NB

    W1NB XML Subscriber QRZ Page

    If you’re going to service several USB devices, as Steven points out most devices draw far less than 2A. LM7805 regulators are cheap. You can hang several off a the 9V feed Steven describes above. Use one for each USB port.
  4. AG6QR

    AG6QR Premium Subscriber QRZ Page

    I've done that, except that I only used one 7805 to feed twin USB outlets (and I can't recall ever using both outlets at once). I used it for phone charging from a 12VDC supply. Dropping 12VDC to 5VDC means the regulator is wasting more power than its delivering, and you definitely need a good heat sink for this. But it works, at least for modest loads.

    If you want something that will deliver a bit more current, add a pass transistor. A reasonable starting point for a simple design is the Elenco XP-720K, described in detail in their manual

    That supply is a triple-output supply, with two variable-voltage outputs, plus one fixed-voltage output of 5VDC at up to 3A. Ignore the variable-voltage outputs, and look at the schematic for the 5V portion (the bottom of the schematic). It uses a simple, cheap 7805 linear regulator, combined with a 2N6124 pass transistor. There's a good explanation on page 16 of the manual linked above describing how the circuit limits the current, so that the supply can safely handle a short-circuited output -- it folds back and doesn't burn anything out. I have one of these supplies, and it works as advertised.
  5. G0GSR

    G0GSR Ham Member QRZ Page

    I would vote for a separate 1 or 2A linear regulator for each output. Then if one device fails, it has a sensible current limit and the other devices continue to work.

    KL7SG likes this.
  6. G4COE

    G4COE Ham Member QRZ Page

    KD7FQI likes this.

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