Dual PWM relay driver with diagnostics for functional safety system

A component comprising:

• a first switch connected to a power source of a safety relay, the first switch comprising a semiconductor switch;
• a second switch connected between the first switch and a first connection of a coil of normally open contacts of the safety relay, the second switch comprising a semiconductor switch;
• a first microcontroller connected to control the first switch, wherein a first output signal of the first microcontroller comprises one of a close signal that closes the first switch and a first pulse-width modulation (“PWM”) signal with a first duty cycle that opens and closes the first switch on each PWM cycle;
• a second microcontroller connected to control the second switch, wherein a second output signal of the second microcontroller comprises one of a close signal that closes the second switch and a second PWM signal with a second duty cycle that opens and closes the second switch on each PWM cycle, the first duty cycle is different from the second duty cycle;
• and
• a comparator with an input connected to a second connection of the coil and an output connected to an input of the first microcontroller and an input of the second microcontroller, wherein the comparator inverts the received PWM signal from the second connection of the coil,
• wherein the first microcontroller sends the first PWM signal while the second microcontroller sends a close signal and the second microcontroller sends the second PWM signal while the first switch sends a close signal,
• wherein the first microcontroller inverts the PWM signal from the comparator and verifies that a duty cycle of a resulting PWM signal matches a duty cycle of the first PWM signal while sending the first PWM signal and the second microcontroller inverts the PWM signal from the comparator and verifies that a duty cycle of a resulting PWM signal matches a duty cycle of the second PWM signal while sending the second PWM signal, and
• wherein the first microcontroller opens the first switch in response to determining that the duty cycle of the resulting PWM signal does not match the first duty cycle while the first microcontroller is sending the first PWM signal and wherein the second microcontroller opens the second switch in response to determining that the duty cycle of the resulting PWM signal does not match the second duty cycle while the second microcontroller is sending the second PWM signal.

A system comprising:

• an electrical component;
• and
• a safety relay controlling power to the electrical component, wherein the safety relay comprises:
• a first switch connected to a power source of a safety relay;
• a second switch connected between the first switch and a first connection of a coil of normally open contacts of the safety relay;
• a first controller connected to control the first switch with a first output signal comprising one of a close signal that closes the first switch and a first pulse-width modulation (“PWM”) signal with a first duty cycle that opens and closes the first switch on each PWM cycle;
• a second controller connected to control the second switch with a second output signal comprising one of a close signal that closes the second switch and a second PWM signal with a second duty cycle that opens and closes the second switch on each PWM cycle, the first duty cycle is different from the second duty cycle;
• and
• a PWM sensing circuit connected to a second connection of the coil that sends a sensed PWM signal to an input of the first controller and an input of the second controller,
• wherein the first controller sends the first PWM signal while the second controller sends a close signal and the second controller sends the second PWM signal while the first switch sends a close signal, and
• wherein the first controller verifies that the received PWM signal matches the first PWM signal while sending the first PWM signal and the second controller verifies that the received PWM signal matches the second PWM signal while sending the second PWM signal.