Exit Sign With Battery Protection

Posted on Feb 5, 2014

This circuit substitutes two white Luxeon 1W Star LEDs for the inverter and fluorescent tube in a standard battery-backed illuminated exit sign, as used in commercial premises. While the Luxeons have less light output than a standard small fluorescent tube, their directional light is quite adequate for the purpose and they do result in less curren

Exit Sign With Battery Protection
Click here to download the full size of the above Circuit.

t drain from the battery. However, the use of a 6V SLA battery for this application means that it can be completely discharged if the 240VAC mains supply is absent for a long period, as can happen when the power to vacant premises is switched off. Such a complete discharge will effectively destroy the battery and must be avoided. This circuit achieves this by switching off Q1 & Q2 when the battery voltage falls below 5. 5V, as set by trimpot VR1. For voltages below 5V, the current drain falls to below 200 µA.

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