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November 29, 2014, 02:30:14 AM
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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  Workbench Power Supply 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Workbench Power Supply  (Read 544 times)
yano
Posts: 180


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Workbench Power Supply
« on: March 03, 2004, 11:16:48 PM »

I scored an 18V Danelectro zero hum wallwart from my local music store after a mix up with some patch I bought. They couldn't give me a refund (the difference between the two cables was $4) so I asked them what else they could offer, and they had this supply in a dusty corner.

Its a 180mA 18V supply, the DA-2. I happen to have some LM317s and I was wondering how to wire them up for 9V output. After reading the datasheet, I came up with this:



Any suggestions?
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Nasse
Posts: 2329

Eagle eats a piece by piece


Workbench Power Supply
« Reply #1 on: March 03, 2004, 11:30:29 PM »

LM317 has good reputation, and maybe lower noise than 78XX

There are circuits floatin around with a pot so you can adjust the exact output voltage and with some caps and a transistor in the control leg you can make it "soft-start" so that the output voltage rises slowly (in some mixer/audio circuits it prevents pops and nasty clicks that can blow your speakers at power on)

Have you considered bipolar power supply too :wink:
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niftydog
Posts: 2006


Hey you're a dog, a BIG dog, a nifty-keen-type dog


Workbench Power Supply
« Reply #2 on: March 03, 2004, 11:43:26 PM »

looks ok, but I get more like 10.8VDC output from those resistor values.

You should include 0.1 and 1 uF caps as per the data sheet to be sure.

Also, consider that the device will be dropping a lot of voltage accross it and it may require a heat sink to keep it cool!  Depends on the current you plan to draw from it, but if you think about it for a sec;

say you're drawing 50mA the device is disipating about half a watt!

Consider what Nasse suggested.  Using an op amp to create a virtual ground might give you a nice bipolar 9VDC supply!
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niftydog
Shrimp down the pants!!!
“It also sounded something like the movement of furniture, which He
hadn't even created yet, and He was not so pleased.” God (aka Tony Levin)
Nasse
Posts: 2329

Eagle eats a piece by piece


Workbench Power Supply
« Reply #3 on: March 04, 2004, 07:23:07 AM »

Quote
Consider what Nasse suggested. Using an op amp to create a virtual ground might give you a nice bipolar 9VDC supply!


I was thinkin a real bipolar supply for op amp circuits would be useful for home lab. Now I have one, I just did quick and dirty one on stripboard, used a single secondary transformer (old battery charger) and two diodes few caps and 7808 7908 regulators.
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petemoore
Posts: 18795


As Yet Unrated


RS
« Reply #4 on: March 04, 2004, 10:09:34 AM »

I got a 317 from RS, use it to regulate my EZ Vibe
  I used the schematic on the back of the package that shows the pot.
  I used it to set my low battery indicators and other stuff...works great!
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