Emergency lighting includes lighting that is used for path of egress illumination upon the loss of normal AC power. Some emergency LED lighting systems include a battery charger, a battery, and a transfer switch to energize the light source upon the loss of normal power. Some emergency LED lighting systems can use additional circuitry to convert a voltage of the battery to a voltage level suitable for the associated light source since LED light sources or light engines are available in a wide range of voltage levels and current capabilities.
An emergency LED lighting system can implement a feed forward technique to maintain approximately constant power. In some aspects, the battery discharge current can be controlled to maintain input power to a DC/DC converter. The power to the LED source can be controlled since the DC/DC converter losses are relatively low and do not significantly impact the output power. Some emergency LED lighting systems include a circuit with a flyback DC/DC converter. The leakage inductance of a flyback transformer introduces energy losses, and additional circuitry (e.g., a snubber circuit) may be included to absorb the losses. In addition, the magnetic core of the transformer may be driven in a single direction, which can reduce the transformer utilization. The flyback design can also have higher peak currents than some other DC/DC converter types. It would be advantageous to provide a constant power emergency lighting system that does not require a flyback converter to avoid these losses, additional circuitry, and transformer under utilization.