Abstract

Module-level Power Electronics (MLPE) are devices that can be incorporated into solar photovoltaic (PV) systems to improve power yield performance in certain conditions, especially where shade is present, and achieve some other system benefits. MLPE are once costly specialty products, but have made great strides in the last decade and been becoming one of the fastest growing market segments in the solar industry. A solar power optimizer is one kind of MLPE that optimizes power output and increases efficiency, which requires the MLPE to have high-power conversion efficiency and low self-heating.

The conventional solar power optimizer commonly uses P-N junction diode or Schottky diode for the bypass circuit. When high current flows through the diode, this can have high power dissipation and bring severe thermal issue because of diode’s relatively high forward voltage drop. The improved method uses MOSFET with lower voltage drop than diode to overcome the high power loss drawback of diode. However, MOSFET needs extra control to turn ON or OFF and the control circuit has control failure probability. This increases the circuit complexity and reduces module reliability. This application note provides a new bypass circuit design using TI’s ideal diode controller LM746x0-Q1 to solve these challenges. In addition, a remarkable idea using depletion MOSFET to extend the reverse voltage range of LM746x0-Q1 to support PV panel with wider output voltage, is also discussed in detail. In addition, this bypass circuit design can be also used in rapid Shut Down (RSD), also regarded as one kind of MLPE, and PV junction box, where traditionally uses diode.