AN604 Datasheet, PDF (9/12 Pages) STMicroelectronics – Calculation of conduction losses in a power rectifier

AN604
An application example
3.1
Average and rms current calculation
The first step is the calculation of the average and rms currents.
The forward average current is the output current: I_F(AV) = I_load = 4.7 A.
As illustrated in Figure 6, the forward current has a trapezoidal shape. The formula to
calculate the rms current of trapezoidal waveform is given in Figure 4. I_F(RMS) is then:
Equation 15
I_F(RMS) =
(11.8)² + (4)² + 11.8 ⋅ 4 _{⋅ 0.6 = 6.4 A}
3
3.2
V_T0 (T_j) and R_D (T_j) calculation
The second step is the calculation of V_T0 (T_j) and R_D (T_j) in the application condition range.
Figure 7. STPS30M100S forward voltage drop versus forward current
I_FM
(MTa^j x=im1u2m5
°C
values)
I _Max = 11.8A
(TTyp^{j =ica1l2v5a°luCes)}
I _Min = 4A
(MTa^jx=im2u5m°Cvalues)
0.52V
0.43V
0.55V
0.63V
T_jref1 = 25 °C and T_jref2 = 125 °C. To calculate maximum conduction losses, read maximum
values of V_F at I_Min and I_Max in Figure 7. This figure is available in the STPS30M100S
datasheet. These values are summarized in Table 1.
Table 1. V_F(Max) values at I_Min and I_Max
I_F (A)
V_F(Max)(I_F, 25 °C) (V)
I_Min = 4
I_Max = 11.8
0.52
0.63
V_F(Max)(I_F, 125 °C) (V)
0.43
0.55
Doc ID 3607 Rev 3
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