Author Topic: Workbench Power Supply  (Read 1016 times)

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Workbench Power Supply
« on: March 03, 2004, 07:16:48 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?


Workbench Power Supply
« Reply #1 on: March 03, 2004, 07:30:29 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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Workbench Power Supply
« Reply #2 on: March 03, 2004, 07:43:26 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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Workbench Power Supply
« Reply #3 on: March 04, 2004, 03:23:07 AM »
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.


« Reply #4 on: March 04, 2004, 06:09:34 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 great!
Convention creates following, following creates convention.