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Ts [ C ]

Rq,rad

[ C/W]

29-6. PMOSFET,max = 150! C!!-!50! C!

!1! C/W = 100 W ; 100 W = 50 + 10-3 fs

Solving for fs yields fs = 50 kHz

29-7. PMOSFET = 50 + 10-3 2.5x104 = 75 W

Rq,ja = Rq,jc + Rq,ca = 150! C!!-!35! C!

!75!W = 1.53 C/W

Rq,ca = 1.53 - 1.00 = 0.53 C/W