powering a 12V device from 18V DC Brick

[dachshund]

I use the DC Brick power supply, which has three 18V outputs along with several 9V jacks.
I got a new wireless system, and the receiver takes 12V for power. My old receiver needed 18V, and worked fine on the DC Brick.

To get 12V, is it sufficient to build a voltage divider, and maybe add the diode reverse-protection and a cap? In other words, this is a regulated 18V DC, so I don't think I need the regulated power-supply circuit. Am I correct?

Thanks in advance.

[petemoore]

  I would use a voltage regulator, instead of a voltage divider.
  LM317 is what I've used for small voltage drops, maybe a 7809 would be more applicable somehow.

[Seljer]

^or 7812 if you need 12V

[PerroGrande]

Yep -- use a 7812 to get 12v from the regulated 18v output.  Well, that is, unless you need more than about 1A of current. 

[dachshund]

Sorry if this is a dumb question, but what's the benefit of the 7812 - more current? The 18V is already regulated.
I'm curious to know. Thanks again.

[grapefruit]

No, you can't get enough current from a voltage divider unless you use low value, high wattage resistor and even then most of the current is wasted. Why would you not want to use a regulator?

Just use a 7812 with a heatsink. It only has to drop 6V and most wireless mic receivers I've seen only draw a couple of hundred mA so you'll only need a small heatsink.

Cheers,
Stew.

[dachshund]

Great, thanks!

[Processaurus]

Here's an easier way, stick a 6v zener diode in series with the 18v (cathode to the +), and there's 12v.  Only thing to look out for is the power rating on the zener, you could use a .5 amp one to be safe.

[sfx1999]

That would require a 6 Watt zener. It would probably be better to just use a 7812. Don't forget your thermal grease if you use a heatsink.