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:
(http://yano.lardpirates.com/electronics/reference/schematics/lm317_18-9.jpg)
Any suggestions?
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:
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!
QuoteConsider 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.
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!