Figure 1 A series diode protects systems from reverse polarity but wastes power in diode losses. Figure 2 You can use a bridge rectifier so that your system works no matter what the input polarity is.

Have you ever needed to power a 12-volt relay in a circuit but only had 6 or 9 volts available? This simple circuit will solve that problem. It allows 12-volt relays to be operated from 6 or 9 volts, ...

The addition of a components and an unused NC contact to a dc supply provides a power-reducing feature to a relay driver circuit. Electromagnetic relays need much less power for holding than they do ...

Last column, I wrote about various applications where fire alarm relays could be used to integrate a commercial fire alarm system with other electrical systems at a ...