TELEPHONE SET CIRCUIT

PURPOSE:To facilitate the on-hook detection of an exchange by providing a timing circuit which generates a pulse for a certain constant time from the moment of on-hook operation and an electronic switch which closes the DC loop of a telephone line with the pulse. CONSTITUTION:The timing circuit 2 and switch circuit 3 are connected to the DC output terminal of a rectifier 7. Then a DC voltage is developed between DC output terminals 71 and 72 of the rectifier 7 by the closure of a hook switch 4 at the time of off-hook operation and applied to the timing circuit 2. The timing circuit 2 generates the pulse signal E for the constant period from the moment. The switch circuit 3, on the other hand, is so constituted as to make its contact with the pulse signal E from the timing circuit 2, so the DC output terminals of the rectifier 7 are short-circuited with low resistance throughout the period of the pulse E to form the DC loop of a telephone line 6 in parallel to a speaking circuit 1. Consequently, the off-hook state of an exchange is easily detected.