Reset from Multiple Power Supplies

Processor based systems usually require a voltage supervisor chip to produce a clean reset pulse to the processor whenever a ‘brown-out’ condition of the power supply is detected. More complex designs employing multiple power supplies can be unreliable if some of the supplies are not supervised. The circuit described here monitors all the supply rails in the system (here +12 V, –12 V and +5 V) and provides a reset pulse to the processor whenever it detects any are not within tolerance.