Duty Cycle = Single Pulse
Allowed avalanche Current vs
avalanche pulsewidth, tav
assuming ∆ Tj = 25°C due to
avalanche losses. Note: In no
case should Tj be allowed to
Fig 15. Typical Avalanche Current Vs.Pulsewidth
BOTTOM 50% Duty Cycle
ID = 140A
100 125 150
Starting TJ , Junction Temperature (°C)
Notes on Repetitive Avalanche Curves , Figures 15, 16:
(For further info, see AN-1005 at www.irf.com)
1. Avalanche failures assumption:
Purely a thermal phenomenon and failure occurs at a
temperature far in excess of Tjmax. This is validated for
every part type.
2. Safe operation in Avalanche is allowed as long asTjmax is
3. Equation below based on circuit and waveforms shown in
Figures 12a, 12b.
4. PD (ave) = Average power dissipation per single
5. BV = Rated breakdown voltage (1.3 factor accounts for
voltage increase during avalanche).
6. Iav = Allowable avalanche current.
7. ∆T = Allowable rise in junction temperature, not to exceed
Tjmax (assumed as 25°C in Figure 15, 16).
tav = Average time in avalanche.
175 D = Duty cycle in avalanche = tav ·f
ZthJC(D, tav) = Transient thermal resistance, see figure 11)
Fig 16. Maximum Avalanche Energy
PD (ave) = 1/2 ( 1.3·BV·Iav) = DT/ ZthJC
Iav = 2DT/ [1.3·BV·Zth]
EAS (AR) = PD (ave)·tav