You could try the ST L272 1 ampere output op-amp, that should have pretty low output impedance.
Put decoupling on the divider but not (directly) on the op-amp output. Something resembling the Zoebel network usually found on audio amp outputs might be worth trying.
What is a good way to generate a DC bias? I'm using an op amp to buffer a voltage divider but I'm worried it may have issues with it's output impedance(Obvious the DC bias should require much current but I'd rather have a too low output impedance than too high). I've also read that it may not be that good because of stability reasons at "low frequencies".
What will the opamp have to drive?
John
a
ay
Exactly, 10k ohm on the output is no problem.
George H.
Huh?
How low of an output impedance do you need, and over what frequency range? Even cheap old things like the LM353 should have an output impedance below 1 milliohm at DC. It just goes up from their unless you do something fancy, but isn't that good enough?
And what sort of low frequency stability problems are you anticipating, at what frequencies?
Huh?
How low of an output impedance do you need, and over what frequency range? Even cheap old things like the LM353 should have an output impedance below 1 milliohm at DC. It just goes up from their unless you do something fancy, but isn't that good enough?
And what sort of low frequency stability problems are you anticipating, at what frequencies?
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1mOhm? All the op amps I have looked at recently have anywhere from 5mA to 30mA output current when shorted. At 10V this would be and effective output impedance of 300ohms to 2kohms.What I'm worried about is the bias not being stable all the time. The op amp will be driving all the biases needed and needs to act like a low impedance source and sink.
I read somewhere that the op amp bias has low frequency issues in some app note. It think it was about single supply's. They didn't give any more information about it.
r u o
ut
An ideal op-amp will have an output impedance of zero, due to negative feedback that keeps the output voltage constant regardless of load current changes. But if the load current exceeds the maximum rating of the op-amp, the output voltage will fall, because it just can't do that. So, you really can't use the shorted condition to measure much, other than what the maximum current might be. But in the real case, the output impedance will be something a little more than zero, maybe a few milliohms.
-Bill
amp
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p
I like the National C-load opamps, like LM8261, for driving Vref type busses that may have substantial current or capacitive loads. They are interesting in that added load capacitance just reduces the frequency of the dominant compensation pole, unlike most opamps where capacitance on the output adds another pole.
John
r
I was half tempted to say a grid leak.
out
amp
ce
The point of opamps is their high gain, which causes the feedback network to stabilise teh output very effectively. It doesnt then matter that the open loop output impedance isnt low, the closed loop impedance is.
If you're generating the bias for opamp input biasing, any old opamp should do a fine job.
NT
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