Power Supply with Battery Backup

This is an incomplete version of the power supply used for the Alertness Monitor with hourly LED Display. This circuit used a Dual Color LED. Green meant Alert and Red meant No Alert or acknowledge press.

I can write here only in “Electronic English”. Focus on the tech not grimmer. It may be like Pascal with a touch of Acronyms, codes and circuit axioms.

The top part is a 5V regulator with 0.7 Diode boost, means 5.7 V DC. The battery was floating on this point above the zener Z4, that connection comes from outside. A protection fuse maybe needed in case Zener draws more current. The Zeners were test selected to get above 6V along with the diode.

The second supply is to drive the LED array and Relay. This second battery supply was needed to prevent the RAM from losing data and also the CMOS logic getting reset, when the relay solenoid operates. Even when the Display Now switch is pushed, the current is large and the pulse could reset digital circuit.

The battery was used very less, it worked during the power failures for short duration between mains and generator switching. This circuit is not meant for in situations when battery drains are high.