MOSFET Switching

开关结构

6.1 Quantized Conduction Gate Resistance The conduction gate resistance Rg(ON) is selected based on the switching time tsw to achieve the desired switching performance. To calculate the gate resistance, we need to know the power supply voltage VDD (or VBS), the equivalent on-state resistance of the gate driver RDRV(ON), and the switching parameters of the device (Qg, Qgd, and Vgs(th)). The switching time is defined as the time taken to reach the platform voltage, where the total charge Qgd + Qgd is provided to the MOSFET, as shown in Figure 21.The calculation for the gate conduction resistance is as follows:[ Rg(ON) = \text{Function of } VDD, Qg, Qgd, Vgs(th), \text{and } RDRV(ON) ] ### 6.2 Output Voltage SlopeThe conduction gate resistance Rg(ON) also controls the output voltage slope dVOUT/dt. When the output voltage is nonlinear, the large output voltage slope can be approximated as:[ \frac{dVOUT}{dt} = \frac{Ig(avr)}{Cgd(off)} ]Where Cgd(off) represents the Miller capacitance (also defined as Crss in the datasheet). ### 6.3 Quantized Gate Resistance in Off-StateThe quantization of the off-state gate resistance occurs when external actions force rectification when the MOSFET's drain is in the off-state. In this case, the output node's dV/dt induces a parasitic current to flow through Cgd, towards RG(OFF) and RDRV(OFF), as shown in Figure 22.The gate threshold voltage Vgs(th) and the drain-source dV/dt are related in the following equation:[ ISINK \geq \frac{1.5 \times QG}{tSW} ]Finally, the total resistance is determined by:[ RTOTAL = Rg(ON) + RDRV(ON) + \frac{VDD}{Vgs + Ig(avr)} ] This equation links the total resistance with the gate voltage and output voltage slope, ensuring that the switching characteristics meet the specified parameters.

讨论了基于MOSFET和IGBT技术的单相全桥逆变器设计，以及其如何与电阻性负载R连接的应用。