How do you calculate power dissipation in a MOSFET?
When a heat sink is attached to a MOSFET, power dissipation is calculated from the sum of 1) channel-to-case thermal resistance (internal thermal resistance), 2) insulator thermal resistance, 3) contact thermal resistance, and 4) heat sink thermal resistance.
What causes switching losses?
Switching losses occur when the device is transitioning from the blocking state to the conducting state and vice-versa. The energy dissipated in each transition needs to be multiplied by the frequency to obtain the switching losses; Conduction losses occur when the device is in full conduction.
How can switching losses be reduced?
The faster the rise or fall time, the smaller is the loss during the transition time, but the switching frequency factor is present, and so it must be remembered that in order to reduce the switching loss, both the switching transition time and the switching frequency must be considered.
How to calculate power loss in switching MOSFETs?
To calculate true power loss in the growing array of applications in the low-to-mid-power range, engineers must carefully consider the impact of switching losses in these applications, and the fundamentally different performance capabilities inherent in trench and lateral MOSFETs.
What happens to Coss when the MOSFET is turned off?
When the MOSFET is turned off, the stored energy in Coss discharges via the body diode and causes the turn-on loss. Theoretically, the Coss loss can be modeled by: The formula shows the power loss caused by Coss is proportional to Coss value, the switching frequency, fswitch and squared drain-source voltage, Vds.
Why is crossover loss lower in lateral MOSFETs?
Crossover loss is a function of the switching speed of the MOSFET (gate resistance, gate source capacitance, and gate drain capacitance). For a given gate drive, lateral MOSFETs achieve faster transition which results in lower crossover loss as compared with a trench MOSFET. Lower crossover loss contributes to lower losses in a number of ways.
How is power loss related to switching frequency?
The other source of power loss is through switching losses. As the MOSFET switches on and off, its intrinsic parasitic capacitance stores and then dissipates energy during each switching transition. The losses are proportional to the switching frequency and the values of the parasitic capacitances.