Regulating to 12V from 9V...

[mydementia]

In light of the recent discussions on power supply filtering and regulation, I'm wondering what the best way (easiest, safest, cheapest) to get 12VDC out of a 9VDC supply.  None of the threads I found when searching really seemed to have a definitive answer...

I have a 12VDC wall wart (from an old house phone, I think) that actually puts out 12.1VDC.  Not sure I want to use this unregulated supply...so here I am.

I'm thinking of using a Max1044 to charge pump up from 9V to 17V, then use a 7812 Regulator to get back down to a nice, clean 12VDC.  Any trouble here?  Looks like the 7812 wants 14.5-19V to provide 12V... I was concerned about the heat generated inside the stomper...should I be?  Here's the datasheet I was looking at: http://www.futurlec.com/Linear/7812T.shtml

Thanks for looking.
Mike

[petemoore]

I'm thinking of using a Max1044 to charge pump up from 9V to 17V, then use a 7812 Regulator to get back down to a nice, clean 12VDC.
  This'll work...
   Any trouble here? Don't see why...
    Looks like the 7812 wants 14.5-19V to provide 12V... I was concerned about the heat generated inside the stomper...should I be?  Here's the datasheet I was looking at: http://www.futurlec.com/Linear/7812T.shtml
  If you're not 'pushing' the regulator hard...dropping a few volts off of 17v, I don't think you'll be able to detect any, or very little heat, probably no need for any heat sinks for heat dissipation.

[mydementia]

Thanks Pete - EXACTLY the kind of support I needed!!
Mike

[David]

In light of the recent discussions on power supply filtering and regulation, I'm wondering what the best way (easiest, safest, cheapest) to get 12VDC out of a 9VDC supply.  None of the threads I found when searching really seemed to have a definitive answer...

I have a 12VDC wall wart (from an old house phone, I think) that actually puts out 12.1VDC.  Not sure I want to use this unregulated supply...so here I am.

I'm thinking of using a Max1044 to charge pump up from 9V to 17V, then use a 7812 Regulator to get back down to a nice, clean 12VDC.  Any trouble here?  Looks like the 7812 wants 14.5-19V to provide 12V... I was concerned about the heat generated inside the stomper...should I be?  Here's the datasheet I was looking at: http://www.futurlec.com/Linear/7812T.shtml

Thanks for looking.
Mike

Do you have a goal of recycling this specific transformer?  If not, it strikes me that you're doing substantial extra work.  I believe that it would be simpler and cleaner to just start with a 15-volt wall wart and regulate down to 12V with the 7812.

[mydementia]

David - I agree...that would certainly be the easy way!!
My intention is to run this at typical stomper power (2.1mm 9VDC jack).  I'll probably make the charge pump modular so when I find a 15VDC wall wart, it will be plug and play... but for the moment, the 12VDC wart is all I have...in addition to all my stomper supplies.
Mike

[David]

Ah, got it.  OK, what about picking through a resale shop or flea market for an old cordless power tool that comes with a charger (and the wall wart, of course)?  I'll bet you can find one that delivers 15V easy.  If a wall wart with VAC output is all you can find, don't sweat it.  Rectifying AC is a matter of 4 diodes!

WAIT!  Dude, did you measure the actual output of your wall wart without a load?  Are you SURE about that 12.1V output?  I'm thinking it's probably more like 14.1V without a load - in which case you're home free!

Try measuring it again.  Also make bloody sure you know whether the output is DC or AC.

[mydementia]

Yep, definitely 12VDC - measured 12.1VDC unloaded...
I just picked up a couple 7812's and the guy behind the counter warned me to put a cap as close to the output as possible to eliminate the switching whine... I thought this would be a plug-and-play kind of thing...  I'm trying it out this weekend...I'll let y'all know how it goes.
Mike

[-mick-]

Hi mydementia 
Nice idea... just a question: I'm going to use a DC power source, so which is the maximum output current? 

[FunkyGibbon]

If using a regulated 9V power supply, could one use the charge pump to get 17V, then a voltage divider to bring it back down to 12V?

Would the values of the resistors be 10k and 24k? Add a 100uF electro to ground as well?

i.e. +17V---------
                        |
                        >
                       <  10k
                        |
                        ---------------------  +12V
                        |               |  +
                        >            -----
                       <  24k     ----- 100uF
                        |               |
                      -----          -----
                       ---             ---
                        -                -

Thanks for your help,

Christopher

[alextheian-alex]

If using a regulated 9V power supply, could one use the charge pump to get 17V, then a voltage divider to bring it back down to 12V?

You could do that, but DC-DC SMPS cause all kindsa nasty noise on the power rail.  i always regulate to get it out, but if a simple divider and filter cap do the trick, then go for it.  HOWEVER... you have to consider your current draw and apply Ohm's law.  If you are sucking more than a milliamp or two through that 10k resistor, then you will have no voltage after the divider!!!

[FunkyGibbon]

Very sensible advice, Alex. The regulator method is pretty cheap and simple anyway.

Thanks for your help.