Hi,
I've got this 0-30V 0-2A supply that I would like to use to test my power amplifier channels because it has current sensing/limiting.
I know theres a way with a few resistors and an op amp that you can split a supply creating a 'virtual ground'. Is there a similar technique which I can use but that would allow for the higher currents? Or would 15-0-15 not be enough to test an amplifier (for basic functionality) anyways?
Pete
I've got this 0-30V 0-2A supply that I would like to use to test my power amplifier channels because it has current sensing/limiting.
I know theres a way with a few resistors and an op amp that you can split a supply creating a 'virtual ground'. Is there a similar technique which I can use but that would allow for the higher currents? Or would 15-0-15 not be enough to test an amplifier (for basic functionality) anyways?
Pete
a simple full bridge rectifier would yeild you +/- 22 vdc properly filtered which would be fine for low powered amplifiers
Cheers!!The DIRT®
Cheers!!The DIRT®
I think he was talking about using a DC supply, not a transformer. I don't know of any good way. Sorry I can't help!
....then I would tap into before its rectified...LOL
Had the same problem long ago.cm961 said:
If you can afford it, buy a second one. Very flexible, you'll have 60V or 30-0-30 and anything in between it if required, also practical when two different voltages are necessary...
/Hugo - lives with 2 supplies for years now, they never fight. 😉
If you don't need to supply real power into a load, i.e. if you only want to test if it doesen't blow upon power up and if the output voltage looks normal on a scope, then you could use a reasonably sized voltage divider made out of two resistors and two capacitors.
If you want to really load it you might capacitively couple the load to the plus or minus rail.
If these suggestions work at all and if yes, how well, depends mainly on the amplifier under test (one key parameter is bias current).
Regards
Charles
If you want to really load it you might capacitively couple the load to the plus or minus rail.
If these suggestions work at all and if yes, how well, depends mainly on the amplifier under test (one key parameter is bias current).
Regards
Charles
Sweet, thanks for the info guys. I'll see if I can score another one, or else I'll try the divider thing.
Can I use high power op-amps (like lm3785) to buffer the divider?
Pete
Can I use high power op-amps (like lm3785) to buffer the divider?
Pete
Well, if you are testing the amplifier and you have the LM3875 in the loop you have to consider its bandwidth etc.cm961 said:
I used a split supply with a floating ground where an LM317/LM337 are used as regulators with pass transistors. It is important, however, that you provide a load AFTER the filter caps attached to a common ground -- a few ma is all you ned, you also need a few ma on the output for the regulators to work correctly.
You will occasionally see dual output Lambda linear supplies on the web.
I have two 16v DC - how do I get +-15?
I got two 16V 3.3A and want to get + 15 (or 16) anf - 15...
But is it possible to just plug them in, connect the + to the - and use this point as 0 ???
Mankeponken
I got two 16V 3.3A and want to get + 15 (or 16) anf - 15...
But is it possible to just plug them in, connect the + to the - and use this point as 0 ???
Mankeponken
No doubt you are refereing to Rod Elliot's Rroject 43 (sound.au.com). I have used the version without an op amp to get a 35-0-35 supply. I just use 2kR/5W resistors.
I have not tried the opamp version of P43, but I did model it with LTspice once to confirm my suspicions - the opamps just control the DC offset and only see the offset voltage and very minimal current. You DO need to add a pair of zeners(usually 15V) to provide the opamps' power supply, though. Since you are not likeley to have an offset of more than 1-2V, there is not much danger to the ICs. Actually, I tried absurdly large offsets and as long as it was less than the opamp's (zener) rail voltage there was no problem. I believe the most significant spec for the opamps is price- use the cheapest - this isn't a very demanding application!
Split Rail from Single Supply
In my experience, most of the simpler circuits shown here using a pair of resistors, etc. would only give you a reasonably accurate mid-point ground IF there is little current flowing through that connection, which is not necessarily always the case (e.g. DC offsets in a bridged amp due to thermal drifts).
The one exception is the 2-Transistor Splitter shown in the link in post 10 (Sijosae discrete rail splitter). I have been using a similar circuit for the last year for a 25W class A bridge amp, using power transistors like TIP2955/3055 with relative high bias (>250mA) to make sure it is always working in class A. Works like a treat, and is stable to much less than 0.7V on +/- 15V rails even as the amp warms up and the bias current (5A nominal) changing by as much as 25%.
A similar circuit can also be found in one of John Linsley Hood's books on audio design (forgotten which one now).
Patrick
In my experience, most of the simpler circuits shown here using a pair of resistors, etc. would only give you a reasonably accurate mid-point ground IF there is little current flowing through that connection, which is not necessarily always the case (e.g. DC offsets in a bridged amp due to thermal drifts).
The one exception is the 2-Transistor Splitter shown in the link in post 10 (Sijosae discrete rail splitter). I have been using a similar circuit for the last year for a 25W class A bridge amp, using power transistors like TIP2955/3055 with relative high bias (>250mA) to make sure it is always working in class A. Works like a treat, and is stable to much less than 0.7V on +/- 15V rails even as the amp warms up and the bias current (5A nominal) changing by as much as 25%.
A similar circuit can also be found in one of John Linsley Hood's books on audio design (forgotten which one now).
Patrick
Indeed there is a major drawback using passive components based splitters, coz u may encounter as said drifts low efficiency overall(small current).I used the fake option in amps based in monolithic IC where the requiensts were medium and the results were poor..but for small currents it works well.
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