DocID027309 Rev 1

7/23

AN4638

Description of test conditions and analyses

23

4

Description of test conditions and analyses

The switching performance and temperature characteristics of the IGBT devices were

evaluated at full load steady state operation in “open board” conditions at room temperature

(25 ºC), as well as various operating conditions for the board by stepping the input/output

frequency.

In both the analyses, the full load condition was reproduced by connecting the output of the

board with a resistive load composed of a series of power resistances arranged in parallel

and with a ceramic base in order to reach the total value of about 145 m

Ω. During the tests,

a fan was used to maintain a constant temperature and therefore help keep total resistance

value constant. This external fan was mounted away from the welding machine to avoid any

influence on the thermal performance of the devices. Moreover, in all the tests performed,

the IGBTs were screwed to the same heatsink as per the original mounting arrangement.

In open board conditions (removing the external metal cover of the welding machine) at

ambient temperature (~25 °C), the measurements were performed with the IGBTs

connected with wires in order to allow the insertion of the probes for the scope to record the

signals. Under these conditions, particular attention was focused on the electrical behavior

operation.