Inspired by the question Op amp Power supply splitter with totem pole I played with the buffered rail splitter in LTspice. I placed a current sink as load on the output to simulate the current sourcing and sinking of a connected amplifier with 100mA amplitude and 50Hz. The output is stable to 20µV, so everything is fine (Fig 1).
But when I increase the size from the bypass caps C1 and C2 at output (as one would do to bypass the supply on succeeding amplifier stages) the whole circuit starts to oscillate (Fig 2). For the screenshot I used values of 100u for C1 and C2, but even with 100n the circuit is already oscillating.
- What is the reason for this oscillation with some capacitance between the new ground and the symmetrical supply rails? I would have assumed these caps would even increase the stability, as the feedback to U1 is now somewhat low pass filtered.
- Can I compensate for that behaviour? How?