Patent-family-89430378

An electric Safe Torque Off circuit (STO) arranged for connection to a motor drive (MD) of an electric motor (MT), wherein the Safe Torque Off circuit (STO) is arranged to cause the electric motor (MT) to stop generating torque in case at least one out of at least two conditions is detected. The circuit (STO) is based on connection of first and second electric inputs (I1, I2) arranged for connection to respective first and second external electric switches (SW1, SW2). A pulse generator (PG) connects to the second electric input (I2) and generates an oscillating electric output voltage when powered from the second electric input (2). A modulator (MOD) generates an electric output signal being a modulated version of an electric voltage at the first input (I1) at a rate defined by the pulse generator (PG) controlled by the second input (I2). The output from the modulator (MOD) is applied to an optocoupler (OPT) which generates an electrically isolated output which is applied to two logic comparator blocks (B1, B2). These blocks (B1, B2) serve to drive respective high and low gate driver parts of the motor drive (MD) only in case both of the first and second pulse detection output indicate that a pulse signal is detected by both of the first and second pulse detectors (PD1, PD2). This provides a compact safety function, e.g. for integration into the housing of an electric motor along with its motor drive. Still, the circuit (STO) is compliant with EN ISO 13849-1:2015, PL e category 3 and IEC 61800-5-2:2016 SIL 3.