Understanding MOSFET Characteristics
MOSFET Capacitance and Temperature Characteristics Parasitic Capacitance Parasitic capacitance exists in power MOSFETs as shown in Figure 1. Sometimes known as stray capacitance, parasitic capacitance is unavoidable and typically unwanted that exists between the parts of an electronic component or circuit simply because of how close they are to one another. Capacitance is the ability of a system to store an electric charge. The Gate terminal in a MOSFET is isolated from the other terminals by an oxide film. The silicon under the gate has the opposite polarity to the drain and source which results in the formation of PN junctions (diode) between the Gate, Drain and Source regions. Cgs and Cgd are the capacitances of the oxide layers, while Cds is determined by the junction capacitance of the internal diode. The gate electrode controls the charge carrier flow through the semiconductor channel, contributing to the parasitic capacitance in the MOSFET. Generally, all 3 capacitances (Ciss,Coss,Crss) listed in Table 1 are included in MOSFET specifications. As shown in Figure 2 the capacitance characteristics may depend on VDS (Drain-Source voltage). As VDS increases...
