Solar power is big business. As demand for solar panels grows, there is an increasing need for more compact and energy efficient electronics so that every possible milliWatt of energy harvested from the sun is captured and made available to use.
Photovoltaic inverters convert the DC current produced by an array of photovoltaic cells to AC at local line voltage and frequency, ready to be fed into the grid or used to power an off-grid network. Micro-inverters that connect to just one panel each are also available – ensuring that reduced output from any panel (perhaps because of shade or snow) doesn’t disproportionately affect the output of the total array.
Inverter designers often face the seemingly conflicting requirements of improving performance and minimising losses whilst compacting form factor and ensuring reliability.
Power MOSFETs are typically the preferred switching semiconductor devices for solar panels because they offer a simple-to-drive option that can be switched efficiently at high frequencies. A rating of 600V and 650V are typically used to ensure enough ‘headroom’ for the safe handling of high voltage transients.
Power MOSFETs consist of an inherent body diode. To minimise switching losses and increase system efficiency, fast recovery body-diodes (FRD) are requested depending on the circuit topology. Such FRDs are basically and simply characterised by reverse recovery times (trr). In addition, choosing devices in which the FRD is integrated into the body of the MOSFET can help to reduce component count, save space, simplify design and streamline inventory.
A variety of MOSFETs with integrated body FRDs are now available in different packages. These devices offer trr of just 100ns (compared to 280ns for a standard version) and RDS(ON) as low as 0.23Ω.