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
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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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