One aspect of the invention is an amplifier (10), comprising an input
stage amplifier (20) coupled to an output node (81). The amplifier
(10) further comprises a class D output stage (50), which comprises
at least two switching elements (P1, N1) and coupled to the output
node (81). The amplifier (10) also comprises a control circuit (40)
coupled to the output stage (50). The control circuit (40) is operable
to produce a tri-state output of the output stage (50) in response to a
sensed value proportional to an amount of current that flows to the output node (81).