501 - Loss Calculation¶

Semiconductor conduction and switching loss modeling.

Overview¶

Accurate loss calculation is essential for: - Thermal design and heatsink sizing - Efficiency optimization - Component selection - Reliability prediction

Loss Components¶

Total Semiconductor Losses¶

Conduction Losses¶

MOSFET: $\(P_{cond,MOS} = I_{rms}^2 \cdot R_{DS(on)}\)$

IGBT: $\(P_{cond,IGBT} = V_{CE(sat)} \cdot I_{avg} + r_{CE} \cdot I_{rms}^2\)$

Diode: $\(P_{cond,D} = V_F \cdot I_{avg} + r_D \cdot I_{rms}^2\)$

Switching Losses¶

Where switching energies depend on: - Current at switching instant - Voltage being switched - Temperature (increases with temp)

Temperature Dependence¶

RDS(on) vs Temperature¶

Typical α ≈ 0.004 to 0.006 /°C (doubles at 150°C)

Switching Energy vs Temperature¶

GeckoCIRCUITS Loss Models¶

Setting Up Loss Parameters¶

1. Open semiconductor properties
2. Enable thermal model
3. Enter datasheet values:
4. RDS(on) or VCE(sat)
5. Eon, Eoff at reference conditions
6. Temperature coefficients

Data Entry Table¶

Example: Buck Converter Losses¶

High-Side MOSFET¶

Conduction: $\(P_{cond,HS} = D \cdot I_L^2 \cdot R_{DS(on)}\)$

Switching: $\(P_{sw,HS} = \frac{1}{2}V_{in} \cdot I_L \cdot (t_r + t_f) \cdot f_{sw}\)$

Low-Side Diode/MOSFET¶

Conduction: $\(P_{cond,LS} = (1-D) \cdot I_L \cdot V_F\)$

Inductor Losses¶

DC Copper Loss: $\(P_{Cu,DC} = I_{DC}^2 \cdot R_{DC}\)$

AC Copper Loss (skin effect): $\(P_{Cu,AC} = I_{AC,rms}^2 \cdot R_{AC}\)$

Core Loss (Steinmetz): $\(P_{core} = k \cdot f^{\alpha} \cdot B^{\beta} \cdot V_{core}\)$

Simulation Exercises¶

1. Measure losses at different load currents
2. Compare MOSFET vs IGBT at different frequencies
3. Analyze loss breakdown pie chart
4. Correlate losses with junction temperature rise

Related Resources¶

• 502 - Junction Temperature
• 503 - Heatsink Design