The bypass circuit plays an important role when the optimizer main circuit or the panel malfunctioning. Traditional solar power optimizers use a Schottky diode or a P-N junction diode for the bypass circuit. When the string current is high, the power dissipation of the diode can cause severe thermal issues due to the high forward voltage drop. To reduce the power dissipation of the bypass circuit, another design is using an active MOSFET controlled by the MCU, but the normal operation of the MOSFET relies on the MCU.

In this design, a high reliable and low-power dissipation method is used. The design does not rely on the signal of the MCU for turning on or off, thus the design can bypass the string current with low-power dissipation even when the MCU is not functioning. LM74610-Q1 is used in this design for stand-alone MOSFET control that can work autonomously without any external intervention. The How to use an ideal diode controller as a scalable input bypass switch in solar applications analog design journal article explains the detailed design and working principle for this method. By adding a depletion MOSFET Q_D in the sense path, the reverse voltage range of the ideal diode controller (42V rated) can be easily extended. String current flows through the power MOSFET Q₁ which lowers the power dissipation of the bypass circuit.

Figure 3-11 Bypass Circuit Based on LM74610-Q1