I'm creating an RGB switcher for a car video system and would like to use the MAX466 chip, which needs -5V, GND and +5V. I have no idea how to change normal 12V DC (car battery) to dual 5V.

I found many schematics which convert AC power, but how about 12V DC?

  • 1
    \$\begingroup\$ The MAX466 is obsolete. Can you just go to the newer replacement MAX4026? This also happens to be a single supply chip, i.e. it can run from a single supply up to 11V. \$\endgroup\$ – caveman Jan 27 '15 at 13:30
  • \$\begingroup\$ Is it a requirement that the GND of the MAX466 is on the same level as the negative terminal of the car battery? Otherwise, if you're not going to draw too much current, simple voltage dividers may do the trick. \$\endgroup\$ – user17592 Jan 27 '15 at 13:46
  • 2
    \$\begingroup\$ I wish people would stop recommending voltage dividers, it only really works for references and virtual grounds, and generates a lot of confused questions on this site. DC-DC converters are the preferred solution if you're going to draw more than a few miliamps. The MAX466 draws up to 100ma. \$\endgroup\$ – pjc50 Jan 27 '15 at 13:55
  • \$\begingroup\$ Thank you caveman - I'll definitely check MAX4026. Still I think it would be nice somebody to answer, I've seen many people have problem with this :) \$\endgroup\$ – NoderBlade Jan 27 '15 at 14:00
  • \$\begingroup\$ I used a dc-dc inverter to get -5V on a pcb, but I already had 5V on the board (from buck regulator) so it was just the easiest quick-fix, also I was dealing with very low currents. I'm pretty sure there are also regulators that have both positive and negative outputs. Not sure how easy/cheap they are to implement though. \$\endgroup\$ – I. Wolfe Jan 27 '15 at 14:04

You could try NMH1205DC or any other DC/DC converter with required current ratings. That's what I use to prototype small boards.

  • \$\begingroup\$ Make sure of the current you are planning to draw here, as OP doesn't talk about current. \$\endgroup\$ – AKR Feb 2 '15 at 3:48

As others have pointed out, you can use a newer chip that doesn't require negative voltage.

However, to answer your question directly, here is one way to make a negative voltage from a positive one:

When the switch is on, current builds up in the inductor flowing downwards. When the switch opens, this can only come thru D1, thereby drawing current from C1 and the output.

  • \$\begingroup\$ You should also include the schematic how to down-convert from 12V to 5V. \$\endgroup\$ – Nazar Jan 27 '15 at 16:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.