5 A scalable bypass switch solution using a low-voltage ideal diode controller

The bypass circuit solution uses an ideal diode controller with a floating gate-drive architecture (such as the LM74610-Q1) to drive an external MOSFET and emulate an ideal diode as the bypass circuit so that it is independent from other circuits. Its floating gate-drive architecture can achieve a universal input range, as the gate drive does not respect to ground. In addition, a unusual advantage of this scheme is that it is not referenced to ground and thus has zero quiescent current.

When solar panels and solar equipment operate normally, the bypass MOSFET is off, and the reverse voltage equal to the maximum panel voltage appears from the cathode to the anode pins of the ideal diode controller. However, the reverse voltage (PV+ to PV–) from the cathode to the anode pins of the ideal diode controller can be very high as the PV panel and string transient voltage. In cases where the PV panels are used in series with a very large input voltage range, it can be challenging to design the maximum input voltage range for the bypass circuit. The maximum reverse voltage of the LM74610-Q1 is limited to 45V transient. Thus, currently available ideal diode controller devices are not suitable for solar panels with a rated input voltage of 80V or 125V.

Adding a depletion MOSFET Q_D in the sense path to extend the reverse voltage range of the ideal diode controller sustains this voltage level for any range, as shown in Figure 4. The drain of Q_D connects to output PV+. The source connects to the cathode and the gate connects to the anode of the ideal diode controller.