The STK401-020 has four power transistors, so the thermal resistance per transistor

θj-c is 2.1°C / W. With an assured

ambient temperature Ta of 50°C, the required radiator thermal resistance

θc-a would be:

From expression (1)'

θc-a <(125–50)/15.7

<4.78

From expression (2)'

θc-a <(150–50)/15.7–2.1/4

<5.84

To satisfy both, 4.78°C/W is the required radiator thermal resistance.

From expression (1)'

θc-a <(125–50)/17.6

<4.26

From expression (2)'

θc-a <(150-50)/17.6–2.1/4

<5.16

To satisfy both, 4.26°C / W is the required radiator thermal resistance. This design example is based on a fixed voltage

supply, and will require verification within your specific set environment.

No. 4341-7/9

STK401-020