Foley & Lardner
Ring trip circuit having a simple trip detecting circuit of a high response speed
 In a ring trip circuit, a trip detecting circuit includes a low pass filter connected to opposite ends of a first resistor detecting an AC ringing signal, a diode bridge connected to an output of the low pass filter, a first series circuit connected to an output of the diode bridge and composed of a Zener diode and a light emitting diode of a first photocoupler, so that a phototransistor of the first photocoupler outputs a trip detection signal to a circuit which can be driven with a different power supply. A zero-crossing point detecting circuit has a second series circuit connected to the opposite ends of the first resistor and composed of a second resistor, a second Zener diode and a light emitting diode of a second photocoupler, so that a phototransistor of the second photocoupler outputs a zero-crossing point detection signal to a circuit which can be driven with a different power supply. A ringing signal supplying relay control circuit receives the trip detection signal and the zero-crossing point detection signal, for generating a switching signal at a zero-crossing point of the AC ringing signal. 
NEC Corporation
H H
H04M H04M
inventional inventional
Masashi
Saito