MSK4802 M. S Kennedy, MSK4802 Datasheet - Page 3

• Manufacturer Part Number: MSK4802
• Description: Half Bridge Pem
• Manufacturer: M. S Kennedy

THERMAL CALCULATIONS
PWM duty cycle and switching frequency all factor into power dissipation. DC losses or "ON-TIME" losses are simply
V
duty cycle of 30%, DC losses equal TBD watts. Switching losses vary proportionally with switching frequency. The MSK
4802 typical switching losses at V
switching loss and the turn-off switching loss. Multiplying the switching frequency times the switching losses will result in
a power dissipation number for switching. The MSK 4802, at 5KHz, will exhibit switching power dissipation of TBD watts.
The total losses are the sum of DC losses plus switching losses, or in this case, TBD watts total.
Subtracting TBD°C from the maximum junction temperature of 150°C equals TBD°C maximum case temperature for this
example.
CE
TBD watts x TBD°C/W thermal resistance equals TBD degrees of temperature rise between the case and the junction.
Power dissipation and maximum allowable temperature rise involve many variables working together. Collector current,
Turn-on switching loss + Turn-off switching loss = Total switching losses = TBD + TBD = TBDmJ
Maximum junction temperature - junction temperature rise = maximum baseplate temperature
V
Total switching loss x PWM frequency = Total switching power dissipation = TBDmJ x 5KHz = TBD watts
Total power dissipation = DC losses + switching losses = TBD + TBD = TBD watts
Junction temperature rise above case = Total power dissipation x thermal resistance
APPLICATION NOTES
(SAT) x Collector Current x PWM duty cycle. For the MSK 4802, V
CE
150°C - TBD°C = TBD°C
TBD watts x TBD°C/W = TBD°C temperature rise above case
(SAT) x IC x PWM duty cycle = TBDV x 800 amps x 30% = TBD watts DC losses
CE
=300V and I
CE
=800A are about TBDmJ, which is simply the sum of the turn-on
3
CE
(SAT)=TBDV max., and at 800 amps and a PWM
PRELIMINARY Rev. - 9/07