IXYS Thyristor/Diode Module Types M##501-12io2 to M##501-18io2 8.3 D.C. Thermal Impedance Calculation −t ⎛ τ rt = ∑ rp ⋅ ⎜1 − e p ⎜ p =1 ⎝ p=n ⎞ ⎟ ⎟ ⎠ Where p = 1 to n and: n t rt rp τp = number of terms in the series = Duration of heating pulse in seconds = Thermal resistance at time t = Amplitude of pth term = Time Constant of rth term The coefficients for this device are shown in the table below: D.C. Term rp τp 1 2 1.37×10 7.6×10 -3 4.86×10 -4 8.6×10 -3 -3 3 4 5 0.0114 0.0223 0.0221 0.101 0.56 3.12 9.0 Reverse recovery ratings (i) Qra is based on 50% IRM chord as shown in Fig. 1 Fig. 1 150 µs (ii) Qrr is based on a 150 µs integration time i.e. Qrr = ∫i rr .dt 0 (iii) K Factor = t1 t2 Rating Report. Types M##501-12io2 and M##501-18io2 Issue 2 Page 5 of 10 August, 2011