## 2 Descriptions and Operational Modes Analysis of the Presented Single-Stage LED Driver  
Figure 2a shows the original two-stage driver circuit suitable for supplying an LED streetlight module, which consists of two buck-boost PFC converters with interleaved operation and a half-bridge-type series resonant converter cascaded with a full-bridge rectifier. The two coupled inductors are employed instead of single-winding inductors in order to accomplish buck-boost conversion. Figure 2b shows the presented LED driver with coupled inductors and interleaved PFC feature by utilizing the synchronous switch technique to simplify power switches and integrate the two-stage configuration into single-stage one. Figure 2b shows the presented LED driver for streetlight applications, which combines an interleaved buck-boost PFC converter with a half-bridge-type series resonant converter cascaded with a full-bridge rectifier into a single-stage power conversion. The interleaved buck-boost PFC converter sub-circuit consists of two capacitors (\(C_{in1}\) and \(C_{in2}\)), two coupled inductors (\(L_{B11}\) and \(L_{B12}\); \(L_{B21}\) and \(L_{B22}\)), four diodes (\(D_{B11}\), \(D_{B12}\), \(D_{B21}\), and \(D_{B22}\)), two power switches (\(S_{1}\) and \(S_{2}\)), and a DC bus capacitor (\(C_{DC}\)). The half-bridge-type series resonant converter cascaded with a full-bridge rectifier sub-circuit includes a DC bus capacitor (\(C_{DC}\)), two switches (\(S_{1}\) and \(S_{2}\)), a resonant capacitor (\(C_{r}\)), a resonant inductor (\(L_{r}\)), four diodes (\(D_{o1}\), \(D_{o2}\), \(D_{o3}\) and \(D_{o4}\)), and a capacitor (\(C_{o}\)) along with the LED streetlight module. In addition, coupled inductors (\(L_{B11}\) and \(L_{B12}\); \(L_{B21}\) and \(L_{B22}\)) are designed to be operated in discontinuous conduction mode (DCM) in order to naturally achieve input-current shaping. In addition, the diodes \(D_{B12}\) and \(D_{B21}\) are used to block the current going from the utility-line voltage source into the inductors \(L_{B12}\) and \(L_{B21}\). Besides, the diodes \(D_{B11}\) and \(D_{B22}\) are capable of preventing the inductor currents going back to the input capacitors \(C_{in1}\) and \(C_{in2}\). Since the input voltage of each buck-boost PFC converter (the voltage on the capacitor \(C_{in1}\) or \(C_{in2}\)) is half of the utility-line voltage, the peak current of each coupled inductor  
Figure 1: The conventional two-stage light-emitting diode (LED) driver for streetlighting applications, PFC: power factor correction. and the DC bus voltage will also be half. Because the DC bus voltage is reduced, the presented LED driver is suitable for the applications with high utility-line voltage. Additionally, the input-current harmonics can be reduced by the interleaved operation, so that the size of the input low-pass filter can be miniaturized [20]. Figure 3 shows the utilized control circuit diagram of the presented single-stage LED driver for streetlight applications. With using a constant-voltage/constant-current controller (IC1 SEA05) for regulating the LED streetlight module's output voltage and current, the output LED voltage \(V_{o}\) can be sensed through resistors \(R_{\text{vs1}}\), \(VR_{1}\) and \(R_{\text{vs2}}\), and the output LED current can be sensed through resistor \(R_{3}\). The sensed output signal from pin 5 of the IC1 feeds into the high-voltage resonant controller (IC3 ST L6599) through a photo-coupler (IC2 PC817). Two gate-driving signals \(v_{GS1}\) and \(v_{GS2}\) are generated from pin 15 and pin 11, respectively, of the IC3, to carry out regulation of the LED streetlight module's output voltage and current. Figure 2: (**a**) Original two-stage LED driver circuit; (**b**) the presented single-stage LED driver with coupled inductors and interleaved PFC for streetlight applications. Figure 4 presents the simplified circuit of the presented single-stage LED driver for streetlight applications, obtained while analyzing the operational modes.