SLYT855 May   2024 AFE88101 , DAC161S997 , DAC8551 , LM74610-Q1 , TVS3301

 

  1.   1
  2. 1Introduction
  3. 2What is a solar power optimizer?
  4. 3Output bypass function of a solar power optimizer
  5. 4Output bypass circuit solutions
  6. 5A scalable bypass switch solution using a low-voltage ideal diode controller
  7. 6Working principle of LM74610-Q1 reverse-voltage range extension
  8. 7Conclusion
  9. 8Additional resources

4 Output bypass circuit solutions

There are typically two kinds of solutions for the bypass circuit. The common way to achieve bypass functionality to use P-N junction diodes or Schottky diodes, as shown in Figure 3. It’s low cost, easy to use and can achieve a very high reverse voltage based on the diode selected. There are drawbacks, however, such as a high forward voltage drop (0.5V to 1V), which causes higher power dissipation and larger printed circuit board requirements. In order to overcome the disadvantages of the bypass diode solution, using an N-channel MOSFET, which has a much lower voltage drop and lower power losses (because of low RDS(on)), is an alternative. There are still some drawbacks, however:

  • The MOSFET is not a stand-alone solution – it requires a control circuit to operate it as a switch, usually a microcontroller (MCU) with discrete MOSFET driver circuit.
  • The MCU needs power from the PV panel. So if the PV panel is badly damaged or fully covered by shadows or shade, then the MCU will not work and the MOSFET cannot turn on,
  • In cases when the MCU fails, the MOSFET cannot be turned on, and the bypass path is through body diode of the MOSFET. But body diode of the MOSFET cannot withstand large currents and will accumulate high degrees of heat that can risk fire.
Typical solutions when using a bypass switch in solar optimizers. Figure 3 Typical solutions when using a bypass switch in solar optimizers.

An intelligent way to address the drawbacks of an MCU-based on or off control scheme is to use a stand-alone MOSFET controller that can work autonomously without any external intervention. The LM74610-Q1 family of floating-gate ideal diode controllers from Texas Instruments provides a stand-alone, low-loss bypass switch solution by controlling the external N-channel MOSFET to emulate series diode behavior. These controllers have a floating gate-drive architecture that can operate with an input voltage as low as the MOSFET’s body diode forward drop (approximately 0.5V).

However, as solar inverter power levels increase, and the adoption of higher-voltage PV panels increases, the bypass circuit has a few requirements to make it a better solution than traditional ones. It needs to work with a PV panel voltage ranging from 20V to 150V to make it scalable across multiple platforms, and it should be independent from other circuits.