As the topic says, I'm going to use a 16VAC wall wart to power a DAC. The DAC will have onboard regulation using LM317/337. Basically, I'm doing this to avoid dealing directly with transformers and mains power, as a safety issue. After the rectifier, is it enough to use one large electrolytic (4700 uF) to smooth the ripple before the regulators? What would you guys do in my situation?
I thought the +/- is supplied directly from the wall wart coaxial plug. It came with a schematic of the transformer, but I don't have it on me right now. I'll check tonight.
As for the voltages, I want to end up with +/- 12, +5, +3.3 for the various sections. The current draw should be well under 1 A, but I can't say for sure right now.
As for the voltages, I want to end up with +/- 12, +5, +3.3 for the various sections. The current draw should be well under 1 A, but I can't say for sure right now.
Hi,
using about 2mF per A is usually enough for accepatable ripple before the reg.
Your 4m7F should easily cope.
There was a thread recently where a single AC winding was purportedly giving +-DC output. I am not sure the poster knew what he was proposing, worth searching for and try to fathom his schematic.
using about 2mF per A is usually enough for accepatable ripple before the reg.
Your 4m7F should easily cope.
There was a thread recently where a single AC winding was purportedly giving +-DC output. I am not sure the poster knew what he was proposing, worth searching for and try to fathom his schematic.
Now I understand what I proposed doesn't make sense. I just don't want to mess with transformers. Well, I guess I can try the virtual ground, but in that case, I will need a much higher AC input (~30), which would give +/- 15 pre-regulation. The highest (AC) voltage wall wart at mouser is only 24VAC, so that's not going to cut it. I suppose I will have to either a) go for an external PSU that has dual outputs (+/- 15) or b) just get over my fear of high voltage and get a center-tapped transformer.
I used two half-wave rectifiers to get + and - voltage out of a wall wart. But then my load was small. Just two op-amps in a Linkwitz Transform circuit. It might not work too well if your current draw is unbalanced. I guess using a full bridge and an active virtual ground would be better in that case.
Brilliant! That's exactly what I was hoping for. I should be able to use LM317/337 instead of the fixed regs, right? Thanks, mucho.
Edit: Apparently, there is an update to that project (cleverly P05a), specifically, to use adj regs.
http://sound.westhost.com/project05a.htm
Edit: Apparently, there is an update to that project (cleverly P05a), specifically, to use adj regs.
http://sound.westhost.com/project05a.htm
Thanks, everyone. If you want to see the schematic that I'm planning, here it is:
http://www.cellandtissue.com/ezdac/schematic.pdf
The regulation is in the lower right hand corner.
http://www.cellandtissue.com/ezdac/schematic.pdf
The regulation is in the lower right hand corner.
I've worked up a PCB for a dual supply, which would take an unregulated AC input. This is the first PCB I've ever tried to make, and I'm clearly not knowledgeable about all the "rules", although I've read about many of them. I used ExpressPCB to draw this, and it would be quite cheap ($51 + shipping) to get three boards made with their MiniBoard service. U1 and U2 are LM317/337, respectively.
Hi,
C3 is connected to common on both pins.
$51 is poor value for three small PCBs. Would stripboard meet your standards?
You could squeeze all the components much closer and then you may get 2 or 3 PCBs onto each board.
Can I suggest a few mods?
1. add an additional pad for each cap to allow for different pin pitch.
2. increase the resistor pin pitch by 0.05inch or 0.1inch.
3. add fuses either to input or to output.
4. output caps footprint seems a bit small.
C3 is connected to common on both pins.
$51 is poor value for three small PCBs. Would stripboard meet your standards?
You could squeeze all the components much closer and then you may get 2 or 3 PCBs onto each board.
Can I suggest a few mods?
1. add an additional pad for each cap to allow for different pin pitch.
2. increase the resistor pin pitch by 0.05inch or 0.1inch.
3. add fuses either to input or to output.
4. output caps footprint seems a bit small.
Sorry but that layout requires some attention to achieve anything like good performance. You need to take account of component interactions and utilise starring properly.
To save yourself a lot of hassle you might like to visit my website www.readresearch.co.uk and build the 'quality regulated PSU for op-amp circuits' which does exactly what you are wanting and has a good and tested PCB already
To save yourself a lot of hassle you might like to visit my website www.readresearch.co.uk and build the 'quality regulated PSU for op-amp circuits' which does exactly what you are wanting and has a good and tested PCB already
Thanks, richie. Like I said in my original post, I have never designed a PCB before, so I am using this as a learning experience, in addition to being something that will be useful for the DAC I'd like to make. I am hoping that you could be a little more specific about which parts of my design are not ideal? Otherwise, I could obviously just copy your PCB, but that to me doesn't seem very DIY-ish. It would be more like DSE (Do someone else's).
By the way, there is another PCB designed along the same lines as yours, and I gave a link to it on the first page:
http://sound.westhost.com/project05a.htm
By the way, there is another PCB designed along the same lines as yours, and I gave a link to it on the first page:
http://sound.westhost.com/project05a.htm
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