I've seen two different configurations for charge pumps here on Brian's site and at FSB, one with a split rail supply as seen on the Kingslayer project and also as a straigh 18v supply as seen in the Road Rage project. My question is, I saw how using the split rail supply on the Kingslayer eliminated the need for biasing the inputs at 1/2 VDD with an inverting configuration, but what about with a non-inverting configuration such as the Tubescreamer where you use a resistor connected between the non-inverting input of the op amp and the biasing voltage? Does this mean that the op amp doesn't need to be biased at all?
If I need to be more clear just let me know, I can include some schematics to explain myself I think.
Cheers!
Like so:
Anybody have any pointers? I'm breaking out the Art of Electronics and searching but so far I haven't seen anything for this specific application... Maybe I posted this in the wrong section as well? Any info would be greatly appreciated.
Jeremy
Vgg, Volage reference or whatever you want to call it is a voltage divider setting a mid-point voltage so the opamp can swing up and down it's also know as 'virtual ground'.
The opamp wants to see a bipolar supply but we trick it with that middle voltage which becomes the new ground if you will and ground is the negative voltage as far as the opamp is concerned.
So basically... anywhere there was a V.Ref, with bipolar, it's now ground.
Thanks, that helps to confirm some things. I guess what i'm wondering now is, do I still need to include the resistor between the opamp input and ground? With a Vcc/2 setup the resistor is regulating current to the input from the 4.5v correct?