Just basic fail. So many good ideas and alternatives have been posted, yet the OP keeps looking for something else and seems intent on finding the worst solution.Basic fail or semi epic fail?
We want to know where we stand.
The only solution posted here was the divided down 6.6V or an integrated smps IC since I already said I won't be using an AC wall adapter.Originally Posted by speakerguy79
BTW I swapped out some parts and got the unit cost down to $5.
The virtual ground was a perfect solution using a DC wall wart adapter, and frankly your reasons for not using an AC wall wart adapter are flat out stupid. Every major electronics supplier offers them, and about 25% of the ones I've collected from old electronics are AC output and not DC. They are not hard to find, and they do not cost more. If you are making a product that needs + and - rails using an AC to AC adapter is just a no-brainer. Buy them in bulk and include with your product. Instead you are looking at SMPS stuff - do you even know about EMI compliance or what kind of a hassle you'll be getting into if you go that route?The only solution posted here was the divided down 6.6V or an integrated smps IC since I already said I won't be using an AC wall adapter.
Like I said, basic fail.
Last edited by speakerguy79; 13th November 2009 at 04:26 PM.
I'll re-visit the AC wall adapter I suppose, and I agree it's a better solution for my application if AC wall adapters are both cost effective and easily replaceable. It's just for the most part nearly every single electronic device I have and know of uses DC wall supplys, even devices which I know for sure have opamps with +/- rails. I also know they use DC-DC smps. They may have bigger power requirements than me though.
I don't know how tough EMI compliance is but I don't think it will be a problem since my design is small and my smps is not offline.
Do the video signals have any DC content? Or are they pure AC? I am an audio guy, so I don't know much about video.
"AC", but you often have to have very low cutoff frequencies on your HPF because the nature of video can carry DC level signals + sync tips in which you have to be able to pass signals around 20hz. Also, because video isn't sinusoidal and is more like a staircase function for different color/luminance levels you have to deal with signal droop if you AC couple. It's complicated. You can get a full explanation here:
Get A Grip On Clamps, Bias and AC-Coupled Video Signals - Maxim
OK, that's cool. Just wanted to make sure AC coupling wasn't an option. I will look at the Maxim link tonight.
Thanks for considering my post even though I wrote it when I was miffed. You took my criticism well. For that I am going to try and help out a little extra. I will post back more later tonight when I'm not at work.
Last edited by speakerguy79; 13th November 2009 at 07:19 PM.
No... a 555 timer as a PWM was suggested. That is not a "integrated smps IC" and 555's cheap, very cheep!!The only solution posted here was the divided down 6.6V or an integrated smps IC since I already said I won't be using an AC wall adapter.
It doesn't matter if it's off-line or not... even DC-DC have regulations that must be met.I don't know how tough EMI compliance is but I don't think it will be a problem since my design is small and my smps is not offline.
This all seems like a long and drawn out and overly complicated way of getting a simple power source designed to me.
I would likely just use an of the shelf +- 5 VDC SMPS three wire power pack and then use a pair of LDO regulators in the actual device to get the remaining +- 3.3 VDC power off of the +-5 VDC lines in the actual device.
Or use a 9 - 10 VAC center tapped three wire power pack and then do a simple regulator circuit in the device itself.
All you need is four regulator IC's and 6 small electrolytic capacitors to get a regulated +-3.3 VDC and +- 5 VDC output.
Being its only running at 10's of ma loads they can be standard issue three pin regulator IC's that sell for about 50 cents in reasonable quantity purchases.
Same with the capacitors as well. You would likely need four 6.3 VDC 100 - 470 uf and two 10 VDC 470 - 1000 uf capacitors. Each sells for around 25 - 50 cents in volume purchases also.
Maybe toss in a few snubber caps on each side of the regulators if needed.
Last edited by tcmtech; 14th November 2009 at 03:06 PM.
"When in doubt, LIGHT IT ON FIRE AND SEE WHAT COLOR OF SMOKE IT CAN MAKE!" -- tcmtech
Considering that the output is from an OpAmp, it is unlikely that the current between the "ground" and the power rails would exceed the capability of one OpAmp. Hence this solution:
Last edited by kchriste; 14th November 2009 at 04:13 PM.
Inside every little problem, is a big problem trying to get out.
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