Detection circuit and detection method

摘要

A detection circuit according to embodiments includes a first circuit (19, 19a) and a second circuit (20, 20a) . The first circuit (19, 19a) is turned OFF when an AC voltage to be input to a pair of input terminals (5, 6a) is smaller than a prescribed value, and is turned ON when the AC voltage is equal to or higher than the prescribed value. The second circuit (20, 20a) detects whether the AC voltage is an AC voltage leading-edge controlled by a dimmer (3, 3a, 3b), an AC voltage trailing-edge controlled by the dimmer, or an AC voltage having a continuous phase on the basis of at least one of the value and a gradient of the voltage of the first circuit (19, 19a) when the first circuit (19, 19a) is turned ON while the first circuit (19, 19a) is in the OFF state.