DISCONNECTION DETECTION CIRCUIT FOR PULSE GENERATOR

PURPOSE:To detect the disconnection of a signal wire with simple circuit constitution, by forming a D-phase signal having a width 1/2 that of each of the A-phase and B-phase signals of a pulse generator and applying said D-phase signal, the A-phase signal and the B-phase signal to the logical circuit of a disconnection detecting circuit. CONSTITUTION:The A-phase pulse and B-phase pulse different by 90 deg. in a phase of a pulse generator and the C-phase pulse per one revolution of a motor are added to a D-phase signal forming circuit 3 to output a D-phase pulse having a width 1/2 that of each of the A-base and B-phase pulses. These A-phase and B-phase pulses A, B and the D-phase pulse formed by the circuit 3 are inputted to a disconnection detecting circuit 4. The A-phase, B-phase and D-phase pulses are subjected to logical operation by the logical circuit constituted of XOR elements 5, 6, AND elements 7, 8, 11 and a reversal element 9 of the circuit 4. The output 3 of the element 8 of the circuit 4 is passed through a filter 10 constituted of CR and a disconnection detection signal 4' is outputted from the output thereof and a disconnection detection signal of the C-phase pulse is outputted from the output of the element 11 and disconnection is detected with simple circuit constitution and the reduced number of signal wires.