A signal processing apparatus (1) includes a power supply input (20),
a power supply connection (30) and a power supply output (27). A
supply voltage generator (33) is connected to the power supply input (20)
via disconnection circuit (72). A detector (70), provided in the
area of the power supply connection (30), enables a supply of power to the
power supply output (27) to be detected and, when a supply of power to the
power supply output (27) is detected, enables the disconnection circuit
(72) to be set, via a control circuit (73), to a state in which the
power supply input (20) and the supply voltage generator (33) are connected.
