Low-dropout voltage regulator for stabilizing LEDs drives in dimmable group current sinks
The well-developed constant current sink (CCSK) supplied from a constant voltage source (CVS) has been widely qualified for driving group-parallel strings of power LEDs. This approach takes advantage of current balancing between multiple parallel strings of the LEDs for producing uniform luminous output. However, the drain-to-source voltage vds of the driver MOSFET may move into triode region when the sink current increases since the change of the forward voltage of the string LEDs and the voltage drop on source resistor cannot be compensated with the CVS. In this paper, a low-dropout controlled voltage regulator (LDCVR) is proposed to adaptively well bias the string LEDs and to prevent the sink MOSFETs from working in triode region when dimming for high luminous needs. An experimental to design approach is adopted in design considerations to facilitate the control means between CCSKs and LDCVR so as to stabilize the luminous output uniform with low conduction loss in the sink MOSFETs.
Reliability study of LED driver - A case study of black box testing
Abstract A method to evaluate the reliability of the Integrated Circuit without knowing the details of the internal circuit is developed. This method is called Pseudo Black Box testing because the basic knowledge of circuit theory is needed. In this paper, this black box testing is applied to the reliability study of a commercial LED driver and the circuit degradation model is built. The possible failure mechanisms of the LED driver are proposed and verified through failure analysis.
Ground Fault Protection for Electric Utility Generating Station Medium Voltage Auxiliary Power Systems
Most generating station designs have medium voltage auxiliary power systems with low resistance grounded neutrals.1 In order to provide even higher reliability, the auxiliary power distribution system configurations supply increasingly redundant process equipment.