A by-pass circuit includes a first power MOS with an intrinsic diode, a first conduction terminal coupled to a cathode, a second conduction terminal coupled to an anode, and a control terminal. A tank capacitor is coupled to the anode. A second MOS has a first and second conduction terminals, a control terminal, and a turn-on threshold smaller than that of the intrinsic diode, the first conduction terminal thereof coupled to the cathode and the control terminal coupled to the anode, so the first MOS turns on when the array of cells are sub-illuminated. An oscillator and charge pump are supplied through the second conduction terminal of the second MOS to charge the tank capacitor. A control circuit is coupled to the control terminal of the first power MOS to switch it based upon a voltage of the tank capacitor and sign of the voltage between the cathode and anode.