prof. Sam Ben-Yaakov in this video explains power losses of resistors used in MOSFET gate driver.
This presentation discusses the intricate details of power losses associated with gate drive resistors in MOSFETs, focusing on non-linear capacitance effects during switching events. Understanding these losses is crucial for optimizing gate driver circuits for efficient power dissipation.
Gate drive resistors play a pivotal role in controlling switching characteristics of MOSFETs. This paper examines the power dissipation across these resistors, aiming to refine traditional estimation methods and provide a comprehensive understanding of underlying phenomena.
The basic estimation of power loss in gate resistors is derived from the product of supply voltage and total gate charge, adjusted by switching frequency. This assumes linear capacitive behavior, where energy is equally split between the gate capacitor and the resistor during charging and discharging cycles.
Nonlinear Capacitance and Energy Considerations
Capacitance Types
- Total Capacitance (C_total): Ratio of total charge to voltage.
- Differential (Local) Capacitance (C_diff): Derivative of charge with respect to voltage.
- Energy-Related Capacitance (C_energy): Derived from energy storage calculations.
Energy Storage Analysis
Practical Case Study: MOSFET and IGBT Analysis
Using data from datasheets and experimental plots:
- Observations:
- Presence of the Miller plateau indicates varying capacitance regions.
- Energy-related capacitance is often higher than total capacitance estimates.
- Gate charge characteristics change with current and voltage levels.
- Findings:
- The ratio of energy stored to energy lost is not constant.
- Losses during turn-on and turn-off cycles differ based on operating conditions.
Conclusion
This presentation highlights the limitations of conventional power loss calculations for MOSFET gate drive resistors. By incorporating nonlinear capacitance effects and energy-related capacitance analysis, we achieve a deeper and more precise understanding of power dissipation dynamics.