I'm trying to take a 12V wall wart supply down to 5V @ 0 to 500mA without using a prebuilt regulator. I was thinking to use a voltage divider setup but after doing calculations I would be using 2, 12 ohm resistors in series with the 5V breakout in between them, it sounds off to me.

How can I step down to 5V without sinking massive amounts of current in a resistive bridge or regulator?

  • 1
    \$\begingroup\$ Related info on regulators vs. dividers: electronics.stackexchange.com/q/106718/38335 \$\endgroup\$ – bitsmack Mar 22 '17 at 16:18
  • \$\begingroup\$ Build a DC-DC converter. \$\endgroup\$ – pjc50 Mar 22 '17 at 16:31
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    \$\begingroup\$ Regulators are designed for exactly this task. Why don't you want to use one? What is your actual need/problem? \$\endgroup\$ – Adam Haun Mar 22 '17 at 16:36
  • \$\begingroup\$ The problem with a voltage divider is it's an unvariable resistor. Its output will roll up and down with load. \$\endgroup\$ – Harper - Reinstate Monica Mar 22 '17 at 16:41

You can't, to have any kind of regulation you need active elements which means transistors. So you will either have to have a regulator, a DC to DC converter (both have transistors) or you can use a resistor divider with limited current.

Even using a few 5.1 zener diodes (with a series resistor to limit current) is going to use more current than the resistor divider itself (but you get more 'regulation').

So there you have it, now you know why people were so excited when transistors were developed (vacuum tubes needed a 60V or so rail)

Its probably easier to buy a 5V wall wart that has 500mA, they are only a few bucks and it will save you time.

  • \$\begingroup\$ 200V - 400V+ is quite common on valves. I wish it was as easy as 60V! \$\endgroup\$ – Paul Uszak Mar 22 '17 at 21:45

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