Op Amp Virtual Ground Questions.
Op Amp Virtual Ground Questions.
(OP)
I need to create a virtual ground for a single supply (24V) amplifier circuit that has 8 opamps for active filters and four LM3886 amplifier ICs.
At the moment I am using an LM324 op amp set up as a voltage follower with a VCC/2 divider connected to the input. When I first connected this up to the circuits virtual ground the op amp output (virtual ground) oscillated at about 2MHz. I have since added a 47ohm resistor and a 100nf Cap to the output of the follower set up as a low pass filter and it has stopped the oscillations.
Can I also add a 68uF Cap to the output of the follower for better regulation of the virtual ground? I am worried about overloading the opamp (capacitive loading) or is it ok in this case as the op amp output is not swinging? What is the best way to filter/regulate the virtual ground in this case? Should I also connect caps from V.Gnd to VCC rail? Any other input is appreciated. Thanks.
At the moment I am using an LM324 op amp set up as a voltage follower with a VCC/2 divider connected to the input. When I first connected this up to the circuits virtual ground the op amp output (virtual ground) oscillated at about 2MHz. I have since added a 47ohm resistor and a 100nf Cap to the output of the follower set up as a low pass filter and it has stopped the oscillations.
Can I also add a 68uF Cap to the output of the follower for better regulation of the virtual ground? I am worried about overloading the opamp (capacitive loading) or is it ok in this case as the op amp output is not swinging? What is the best way to filter/regulate the virtual ground in this case? Should I also connect caps from V.Gnd to VCC rail? Any other input is appreciated. Thanks.





RE: Op Amp Virtual Ground Questions.
RE: Op Amp Virtual Ground Questions.
Just a few questions. Good luck and keep us posted!
RE: Op Amp Virtual Ground Questions.
RE: Op Amp Virtual Ground Questions.
I agree that a simple resistive divider will work wonderfully if a ball-park, dynamic mid-rail voltage circuit is required, but I would think twice about using a zener clamp if this must be held constant over temperature (not too mention that the voltage is no longer "guarenteed" to be mid-rail). Even worse, would be to use a op-amp circuit if you intend to drive tens of amps.
I don't want to argue whether your solution will work, because it probably will, but I just want to make sure that DoiNk! (and the rest of the people reading this post), get to understand HOW you came up with the circuit. I have read several of your posts, and have no doubts in your abilities, but I still don't think that we have enough information to give accurate advice. Perhaps if DoiNk! could elaboarte a little more on his/her problem statement, then we determine which solution will work the best.
RE: Op Amp Virtual Ground Questions.
RE: Op Amp Virtual Ground Questions.
Sorry for any confusion. What I am basically trying to do is create a voltage reference that is equal to half the supply voltage (ie, Supply/2). My supply is 24V in this case, so a steady 12V reference is what im after. This voltage will then be used as a midpoint reference for a couple of op-amp (active) filter circuits. High output current is not necessary as the reference is only used to supply small bias currents to the op amps.
Currently, I am using a voltage follower almost identical to what is described on page 2 of this document: http://www.analogzone.com/avt_0806.pdf
I realise there are supply splitter chips available, but i am looking for a cheap/simple solution. I also had a spare opamp available on the board, thats why I decided to go for the follower instead of the basic 2 resistor voltage divider.
What I was originally asking was weather or not I could add a large 68uF electro capacitor also to the output of the follower for better filtering/regulation? I was worried about loading on the op amp.
If you could suggest any further methods of filtering or a better way of creating the half supply reference, it would be most appreciated. Thanks in Advance...
RE: Op Amp Virtual Ground Questions.
RE: Op Amp Virtual Ground Questions.
RE: Op Amp Virtual Ground Questions.
RE: Op Amp Virtual Ground Questions.