power supply monitor - big brother is watching you

july/august 1984 big brother is watching you . . . This monitor circuit is based on the MC 3424 power supply supervisory IC. It provides two-channel over- voltage crowbar protection, which is very useful for floppy disk systems, and overvoltage and undervoltage monitoring of the +5 V line, which is particularly important in micro- processor supplies. Each channel in the MC 3424 has an input and an output comparator. Channel 1 is the undervoltage monitor, while channel 2 provides crowbar overvoltage protection. The input comparators sense the regulated supply line (pins 3 and 15). Each of them provides a common- mode range of 0 . . . (Vcc-1.4 V) volts. The source resistance of the inverting inputs determines the amount of hysteresis. An on-chip generated reference voltage of 2.5 V (available at pin 1) is permanently connected to the non- inverting input (pin 2) of com- parator 1 and to the inverting input (pin 14) of comparator 2. When the voltage on the supply line drops below abo...