Patent ID: 8716936

Claim:
An emergency lighting device for operating a light source, in particular an LED, the emergency lighting device comprising: an energy storage unit, a charging circuit to be supplied with a mains supply voltage for charging the energy storage unit during a charging operation, the charging circuit having potential isolation, and a driver circuit supplied by the energy storage unit during emergency lighting operation, for operating the light source, the device further having a control unit that is designed to monitor the state of the mains supply voltage during the charging operation, and to activate emergency lighting operation upon identifying an emergency state, wherein the control unit determines the state of the mains supply voltage on the basis of the output voltage of the charging circuit, which output voltage charges the energy storage unit, and the charging circuit has a controllable switch that is activated by the control unit, wherein the control unit determines the state of the mains supply voltage taking account of a duty cycle for activation of the switch and of the charging power for the energy storage unit.