| DoiNk! |
I am building a single supply (24V) preamp and amplifier circuit that uses about 8 op amps for active filters and 4 LM3886 amplifier IC's (High and Low Bridged Outputs).
What is the best way to create a steady mid-rail voltage (VCC/2) for a reference voltage (also known as virtual ground) for the opamps and LM3886 IC's?
At the moment, I am trying an op amp follower circuit similar to the one shown on page 2 of this document http://www.analogzone.com/avt_0806.pdf (i originally didnt have the small resistor on the output and got oscillations from the op amp. the small 47R resistor fixed this)
I am using an LM324 op amp for the follower. (have a spare one available on the board). Can I also add a large electrolytic cap (68uF) to the follower output for filtering/regulation? |
|
|
| jackinnj |
| You can use an LM317/LM337 pair (positive and negative regulators). The input to the positive and negative rails go to the appropriate regulator input. The grounds are tied together -- and this is your virtual ground. In fact, for the best results I have used two LM317's and two LM337's -- allowing for the overhead in each. (As described in Audio Amateur sometime in the early 1990's). Make sure to bypass the regulators as shown in the National Semi applications notes and use the appropriate resistors to set the output voltage. I use this technique (beefed up with some power transistors) to derive +/0/- from an old Heathkit regulated power supply and it works fine. |
|
|
| Nelson Pass |
I have always had good luck with a simple pair of
resistors, equal value, set up as a divider to form
a voltage halfway between v+ and ground. Then
put a nice big capacitor from the center point (+)
to ground (-).
Typical resistor values would be a few K and capacitor
maybe 1000 uF. |
|
|
|
