Electronics, PCB Design and PCB Layout Daycounter, Inc.
Engineering Services

Custom Firmware, Electronics Design, and PCB Layout


Water Level Sensor

Heat Sink Temperature Calculator

See our other Electronics Calculators.

Power components have a maximum junction temperature, which must not be exceeded to prevent damage to the device. Devices are encapsulated in packages which have different levels of thermal resistance.  When designing power electronics, the heat dissipation of the device, coupled with any heat sinks, as well as the maximum power dissipated by the device, must be analyzed to insure that the device operates within allowable specified limits. 

This calculator and tutorial computes the junction temperature of a power electronics device given the maximum ambient temperature, and the heat sink thermal resistance. The calculator will let you know if the maximum junction temperature could be exceeded for a given power, and likewise will tell you the maximum power that the device can handle for a given maximum power.  

For automotive applications, use 80C for the ambient temperature.  For maximum junction temperature, 150C is a common value, but check the part's data sheet to be sure.  The junction to case thermal resistance varies by package, see the table below for common values. For the thermal resistance 1 field this could be the case to ambient temperature thermal resistance if there is no heat sink, or if a heat sink is used, it's the thermal resistance of the heat sink.  The second thermal resistance field is not typically used.  

When choosing heat sinks, you want the smallest thermal resistance possible, which means that the heat will be more easily dissipated. 

For surface mount (SMT) parts, where the PCB copper is used as a heat sink, for 1 ounce copper the heat dissipation asymptotically approaches 1 square inch, in other words, having a PCB heat sink greater than 1 inch doesn't do you any good. There are some tricks that can help, such as placing vias, into the pad, so that heat is transferred to the bottom layer as well. It's also possible to use surface mount heat sinks. 

Maximum Ambient Temperature (C)
Maximum Junction Temperature (C)
Thermal Resistance - Junction to Case  (C/Watt)
Thermal Resistance 1  (C/Watt)
Thermal Resistance 2 (Optional) (C/Watt)


Junction Temperature

Typical values of Thermal Resistance for Various Electronics Packages 

Package Junction to Case (C/Watt) Junction to Air (C/Watt)
TO-3 5 60
TO-39 12 140
TO-220 3 62.5
TO-220FB 3 50
TO-223 30.6 53
TO-252   5 92
TO-263  23.5 50
D2PAK 4 35

Thermal Resistance for PCB Copper

Heat Sink Thermal resistance (C/Watt)
1 sq inch of 1 ounce PCB copper  43
.5 sq inch of 1 ounce PCB copper  50
.3 sq inch of 1 ounce PCB copper  56
Aavid Thermalloy, SMT heat sink:  PN:573400D00010 14

Manufacturer Links

The best way to find electronics manufacturers is to use our free Electronics Component Directory, where a myriad of manufactures are listed.

Other Electronics Links

We offer a broad range of electrical engineering calculators and electronics articles and tutorials

Daycounter specializes in contract electronics design.  Do you need some help on your project?  Contact us to get a quote. 


[Employment] [Downloads] [Articles] [Contact Us]

Salt Lake City, UT, USA

Disclaimer: Daycounter, Inc. doesn't guarantee the accuracy of any of it's content. Use at your own risk.

© Copyright 2016 Daycounter, Inc. All rights Reserved.

Soil Moisture Sensor Probe