Question

QUESTION 4(Total 12.5 Marks) The switch current and voltage waveforms of a power converter are shown in the next page. The switch has a maximum junction temperature, T,max140°C and a junction-to-case thermal resistance Rc 0.55°C/w (a) How much power is dissipated by the switch? Sketch the power waveform (7.5 marks) (b) The converter operates in an ambient of 25°C and the switch is mounted on a heat sink. Specify the value of thermal resistance of the heat sink, if a thermal grease with thermal resistance of 0.3°C/W is used (5 marks) 0 on ton o1n T,-100us ton 1 us, toff 1 us loff =0, Von = 2 V, Voir = 500 V, lon = 10 A

Answer 1

a Voss on Torf -toff MG pertod Power disipoted. duarj TON Ve dt Vofp Toton ON Powor dEssnated du tor) ON ON PEmio d o VO and cenp &dmad

(10-50-4)x10 -, Total POusbr - 49/5- 9 Wat Timay 140°C Resc Ampient temperacture(Ta)= 2n0c Themal elfS4ance of Greale Themal esitane of heat sinr (Ko?

Temporadur f rowes diipatiog" The mal st 1+aoce. Y TA Tmay Reg Re ReiReRe 140 0.55t 0.3 t Re Res-03 w