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
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.
Thanks Pete - EXACTLY the kind of support I needed!!
Mike
Quote from: mydementia on November 09, 2006, 10:54:18 AM
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.
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
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.
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
Hi mydementia :icon_wink:
Nice idea... just a question: I'm going to use a DC power source, so which is the maximum output current? :icon_biggrin:
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
Quote from: FunkyGibbon on March 25, 2007, 01:28:58 AM
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!!!
Very sensible advice, Alex. The regulator method is pretty cheap and simple anyway.
Thanks for your help.