Q1 An IGBT and a diode forming a power converter are mounted onto a heatsink. Thermal...

 

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Q1 An IGBT and a diode forming a power converter are mounted onto a heatsink. Thermal data for this arrangement are given in Table Q1. The ambient temperature Tamb is 40C. IGBT Table Q1. Power dissipation WIGBT in IGBT Junction to case thermal resistance Rajc Case to heatsink thermal resistance Rechs 12 W 0.6C/W 1.4C/W Diode Power dissipation WDIODE in diode Junction to case thermal resistance Rejc Case to heatsink thermal resistance Rechs 7 W 0.9C/W 1.5C/W Heatsink Heatsink to ambient thermal resistance Rehsa Thermal capacitance Cens of heatsink 3.2C/W 280 J/C Q1a i. ii. iii. Sketch a clearly-labeled thermal circuit. Calculate the steady-state temperature of the diode and IGBT junctions. Calculate the heatsink's temperature three minutes after the circuit is de-energised after it has been running in the thermal steady-state. 13 marks Q1b You have designed a buck converter, and as part of the design validation programme you need to experimentally measure the converter's switching losses. Thermal superposition measurements or double-pulse testing can be used for this. Describe how these techniques work, and discuss their advantages and limitations. Q1 An IGBT and a diode forming a power converter are mounted onto a heatsink. Thermal data for this arrangement are given in Table Q1. The ambient temperature Tamb is 40C. IGBT Table Q1. Power dissipation WIGBT in IGBT Junction to case thermal resistance Rajc Case to heatsink thermal resistance Rechs 12 W 0.6C/W 1.4C/W Diode Power dissipation WDIODE in diode Junction to case thermal resistance Rejc Case to heatsink thermal resistance Rechs 7 W 0.9C/W 1.5C/W Heatsink Heatsink to ambient thermal resistance Rehsa Thermal capacitance Cens of heatsink 3.2C/W 280 J/C Q1a i. ii. iii. Sketch a clearly-labeled thermal circuit. Calculate the steady-state temperature of the diode and IGBT junctions. Calculate the heatsink's temperature three minutes after the circuit is de-energised after it has been running in the thermal steady-state. 13 marks Q1b You have designed a buck converter, and as part of the design validation programme you need to experimentally measure the converter's switching losses. Thermal superposition measurements or double-pulse testing can be used for this. Describe how these techniques work, and discuss their advantages and limitations.