48v 150W power supply (12V step-up)

This allows 48v equipment to be powered from a 12v battery… ideal for power-over-ethernet devices which need 48v. A commercial DC-DC converter can cost a fortune. This is a fraction of the cost. It is slightly over-engineered, the heatsink can be much smaller. It uses Linear Technology LT1680. Everything runs cool, but the inductor does get hot to touch, but temp probe did not reveal anything remotely worrying over the space of a few hours. I would install a micro fan ideally, there is room in the enclosure for that. Efficiency is around 90%. The board has a MOSFET controlled power feature, so it can be remotely switched on/off. The board is designed to slide into this enclosure(100mm x 80mm size). The recommended inductor was a Magnetics 0077314A7 (http://www.mag-inc.com/) device with 18 turns, but this is not easily obtainable. The option I chose was to purchase a wound choke from Farnell (LCR components model DF6, which is Farnell order code 9520937), cut it apart and remove the wire, and then create my own winding of 16 (not 18) turns of 16SWG (14AWG) wire. This worked fine.

48v top photo

This is the circuit diagram.

This is the layout (double-sided PCB):

top side and bottom side . The layout is the way it is, because of the huge currents involved (12A at 12V). This means there are a few wire links. They are drawn on the silkscreen. They were soldered on the underside as shown here. There are two white fat wires (high current) and one thin blue wire (low current). Note that D3 (top right) was a bit bigger than the pad unfortunately. However it still fits (it is an optional component anyway).


This is the parts list with Farnell order codes for all the important bits. Worth spending money on the capacitors, see the order codes to get the specs if selecting different ones. Note all the heatsink mounted parts need heatsink compound, insulating mica sheet and insulating washer:


To test, a thermocouple was taped onto the inductor, and then some resistors were connected up as a dummy load:

resistor test

If there is sufficient interest, the unpopulated boards (double layer) can be made available for around £15 (25USD). Update – boards now available for £15

Author: admin

8 thoughts on “48v 150W power supply (12V step-up)

  1. Hi Laurian,
    Inductor can be sized for 1.2 x the average current and it should be lower than that, but I need to re-measure it for the detail (I lost my scope traces).

  2. <p>Hi Adam, </p>
    <p>They are available, please send a paypal payment to this email address: (without the spaces or the character X )<br />
    s X y X o u s a f at c X i X s c o dot c o m and send me an e-mail to the same e-mail address with your shipping address. The boards are £15 or $25 USD or 18Euro, and postage in the UK is £2.50 or overseas it is $6 or 5 Euro. If you prefer to pay by card, let me know.</p>

  3. Hi,
    Unfortunately when I replaced my hard disk I didn’t copy across my Eagle folder (annoyingly it was in the Program Files folder). I may one day re-create this board because I’m very happy with it, it has worked reliably. If you re-create it, do please share it if you can. I’d recommend using a much smaller heatsink, since the current heatsink never warms up. I still have some of the boards available for sale.

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