Patent ID: 6292341
Filing Date: 2001-09-18
Classification: H03K

Abstract:
A protection circuit for a diagnostic output of control unit for protecting the control unit in the event of a disconnection from ground or a below ground condition, the protection circuit comprising:first and second transistors, the first transistor having a source connected to ground and a drain connected to the diagnostic output through the second transistor, the second transistor having a source connected to the diagnostic output and a drain connected to the source of the first transistor;a comparator for comparing a voltage of the diagnostic output with a voltage of a reference node of the control unit;a logic gate having a first input connected to an output of the comparator and a second input connected to a gate of the first transistor;a current limiter;a first current generator connected to the current limiter and defining a connection node therebetween, the connection node connected to a gate of the second transistor, the first current generator being controlled by an output of the logic gate for forcing a current on the diagnostic output via the current limiter;a third transistor for switching the second transistor off, the third transistor being connected in parallel to the current limiter; anda circuit for controlling the third transistor, the circuit comprisingan inverter,a voltage divider having an intermediate node,a second current generator, controlled through inverter by the output of the comparator, for forcing a current, through the voltage divider, on the diagnostic output line, the intermediate node of the voltage divider being connected to a gate of the third transistor; anda third current generator connected between the intermediate node of the voltage divider and the reference node, controlled by the output of the comparator in phase with the first current generator and in opposite phase from the second current generator.