Self-diagnostic circuitry for emergency lighting fixtures

Abstract

Electronic self-test and/or self-diagnostic systems particularly useful with emergency lighting fixtures, including exit signage having light emitting diodes as light sources and unit emergency fixtures powered with lead-acid batteries, the systems perform testing and diagnostic functions on the circuitry, power supply, charger and lamping of such fixtures either by manual or automatic initiation. Testing functions are provided through use of a programmable microprocessor, the diagnostic circuitry not only monitoring operation of charger/transfer circuitry but also controlling the charger/transfer circuitry to enable alternate strategies for alleviation of a given failure. In emergency mode of a light emitting diode exit sign, a microprocessor-controlled two-stage inverter is employed not only to power the LED light source, but also to efficiently power the microprocessor. Power to the microprocessor is controlled by the microprocessor itself and can therefore be discontinued after appropriate operation until mains power is restored, thereby effectively reducing power consumption to zero. System operation can be flexibly configured through use of a two-wire serial link between modular elements of the system. Incandescent emergency unit fixtures due to high drain rates and output loads require emergency mode operation through use of lead-acid batteries, thereby requiring voltage controlled charging and relay transfer, the self-test and/or self-diagnostic circuitry of the invention used with emergency unit fixtures thus differing in various respects from the circuitry employed for the LED exit signage fixtures and primarily in the need to measure both charge and discharge currents, the circuitry having a larger dynamic range in addition to a capability of measuring both positive and negative currents.