audioguru Posted April 6, 2010 Report Share Posted April 6, 2010 But I don't know to make this conversion to have the results for the Hfe (159-180 Hfe - 2,5mA) under 1,5A.I always design circuits so that any transistor that meets the minimum or maximum spec's works fine.Are you designing the circuit so it only works with the transistors you measured then it might not work if a transistor is replaced?The minimum hFE is 20 at 4A. The datasheet has a typical curve where the hFE is 35 at 4A and is about 80 at 1.6A. The curve does not show below 100mA. Then the minimum hFE at 1.6A is 80/35 x 20= 45.7. Then the max collector current in the BD139 is 5A/45.7= 109.4mA and it will get very hot when the output is 5A and the voltage is low or is shorted. Quote Link to comment Share on other sites More sharing options...
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