Explain the operation of this circuit
When the switch is set to the 'off' position (closed) the LM3880 goes into its 'power down' sequence with each flag output pulling low in turn (FL3/FL2/FL1). FL3 and FL2 pull the adjust pins of the voltage regulators low through 1k resistors, which forces their outputs high because the feedback voltage divider ratio is 10 times higher than normal, causing them to attempt to output a voltage 10 times higher but actually saturating at close to +5 V.
The voltage regulator outputs go to inverting op amps set to a gain of 1, which produces a negative output voltage proportional the positive input voltage. The inputs are at +5 V so the outputs go as close as they can to -5 V (according the datasheet the saturation voltage is ~1 V, so they should go down to ~-4 V).
When the switch is turned to the 'on' position (open) the LM3880 goes though its 'power up' sequence (FL1/FL2/FL3), releasing each flag output in turn and allowing the voltage regulators to operate normally with adjustable output. Again, since the op amps invert the voltage the positive regulator output voltage becomes a negative Gate bias voltage.