This second switch must be synchronized with the main switch so that reverse current is passed through a parallel silicon carbide (SiC) Schottky diode. This diode has a high breakdown voltage and an extremely low reverse recovery charge so that the effect of Qrr on switching losses is significantly reduced.
With Advanced SRB (A-SRB1) the losses caused by recharging the output capacitance of the main switch are significantly reduced by pre-charging it to a lower voltage. The output capacitance COSS strongly depends on the drain-source voltage VDS. When this is increased from 0V to 40V the capacitance is reduced by a factor of about 100. During turn-on, this voltage dependency causes the main portion of the charging current to flow for low VDS. However, in a half-bridge configuration, a low VDS across the switch being in off-state means a high voltage across the switch turning on, leading to high turn-on losses due to the charging current peak.
If COSS (Q1) of the switch remaining in off-state, is pre-charged before turn-on of the other switch of the half-bridge (the low-side switch in our example) most of the charging current does not flow through the transistor turning on and thus cannot contribute to turn-on losses. The pre-charging is performed by an additional voltage source, which is realised by a charge pump in the gate driver IC.
Based on the A-SRB technology, Toshiba has developed a system solution for PV inverters with an output power of up to 5kW. It consists of four main components:
- The inverter bridge with A-SRB technology
- One MCU for controlling the entire system
- Two analog front-end ICs (AFE) for controlling the DC/DC converter input stages as well as the output inverter.
In addition to the efficiency gains achieved by A-SRB, the two highly integrated AFE ICs contribute to a compact, cost-optimised inverter system.
To learn how Toshiba's integrated A-SRB solution for PV applications can help you convert energy more efficiently, please click here: