A New DC Measuring Method of the Thermal Resistance of Power MOS Transistors Krzysztof Górecki and Janusz Zarębski Department of Marine Electronics Gdynia Maritime University, POLAND

2 Outline  Introduction  Description of the method  Verification of the method  Conclusions

3 Introduction   Thermal resistance describes ability of heat dissipation of semiconductor devices at the steady state   The thermal resistance R th is expressed by   One can distinguish two kinds of methods of R th measuring :   The optical (infrared) methods   The electrical methods   the advantage of the electrical methods is a possibility of estimation of the thermal resistance of both the capsulated and uncapsulated devices

4 Introduction (cont.)   Two groups of electrical methods of R th measuring are known:   The impulse methods   The dc methods   In both the methods the thermo-sensitive parameter is used   The advantage of dc methods is the lack of interferences connected with switching the investigated device and the simple measuring procedure   In the paper a new dc method of measuring the thermal resistance of power MOS transistors is proposed

5 Description of the method (1)   The coordinates of four operating points of the investigated MOS transistor operating in the saturation region should be measured   A(u GS1, u DS1, i D ), B(u GS2, u DS2, i D ), C(u GS3, u DS3, i D1 ) and D(u GS4, u DS4, i D2 )   The coordinates of the points A, B, C and D must meet the following conditions   Using these coordinates the values of the MOS transistor model parameters U P0,  U,  should be calculated,

6 Description of the method (2)   Calculation of the R th value using following formula where  GS is given by

7 Verification of the method   The experimental verification of the new method was carried out for the power MOS transistor IRFR024N placed in the case D-PAK and operating without any heat-sink   The coordinates of the measuring points:  From the new method R th = 75 K/W  From the pirometric method R th = 72 K/W pointABCD u GS [V] u DS [V] i D [mA]

8 Conclusions In the paper the new method of measuring the value of the thermal resistance of power MOS transistors is proposed. The realization of the method is simple and requires only to perform the measurements of the coordinates of the four operating points of the investigated transistor situated inside the saturation region and to carry out some calculations with the formulas given in the paper. It was experimentally shown that the measuremental results obtained with the presented direct-current method are convergent with the results obtained with the pirometric method with the differences between them not exceeding a few percentage. Another advantage of the use of the new method is measuring the value of the threshold voltage U PO of the investigated transistor, the temperature coefficient  U of changing of this voltage and the exponent  describing the dependence of the parameter transductance on temperature.