Online MOSFET Power Loss/Dissipation Calculator and Guide for Engineers
In the dynamic world of power electronics, understanding and minimizing power losses in Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) is crucial for optimizing efficiency and performance. This guide explains the basics of calculating various types of power losses in MOSFETs, including conduction, switching, reverse recovery, deadtime, and gate charge losses.
MOSFET Power Loss Calculator
1. Conduction Loss (P_cond)
Conduction loss occurs when the MOSFET is in the 'on' state and current flows through its channel. It's calculated using the formula:
P_cond = Current^2 × Rds(on)
where Current is the drain-source current and Rds(on) is the on-resistance of the MOSFET.
2. Switching Loss (P_sw)
Switching loss happens during the transition between the 'on' and 'off' states. The energy dissipated in each switching event is proportional to the bus voltage Vbus, current Current, and the sum of rise and fall times (Tr + Tf). Additionally, the output capacitance Coss also contributes to switching loss. The formula is:
P_sw = 0.5 × Vbus × Current × (Tr + Tf) × f_sw + 0.5 × Coss × Vbus^2 × f_sw
3. Reverse Recovery Loss (P_rr)
This loss is associated with the reverse recovery charge Qrr of the internal diode in the MOSFET and is significant in high-frequency applications. It's calculated as:
P_rr = Qrr × Vbus × f_sw
4. Deadtime Loss (P_dt)
Deadtime loss occurs due to the body diode conduction during the interval when both the high-side and low-side MOSFETs are off. It's a function of the body diode forward voltage drop Vsd, current Current, and the sum of turn-on and turn-off delays (Td(on) + Td(off)). The calculation is:
P_dt = 2 × Vsd × Current × (Td(on) + Td(off)) × f_sw
5. Gate Charge Loss (P_gate)
Gate charge loss accounts for the energy required to charge and discharge the gate capacitance of the MOSFET. The total energy for one complete cycle of operation is double the energy required for a single charge or discharge. The formula for calculating this loss is:
P_gate = 2 × (Qg × Vgate_drive) × f_sw
6. Output Capacitance Loss (P_coss)
The output capacitance loss is associated with the energy stored in the output capacitance Coss during each switching cycle. This energy is lost whenever the MOSFET is turned on or off. The formula is:
P_coss = 0.5 × Coss × Vbus^2 × f_sw
Summary
This guide provides an introduction to the power dissipation characteristics in MOSFETs under various operating conditions. These calculations are helpful for anyone looking to understand the efficiency and performance of MOSFET-based power electronic systems.
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