Heat sink with transistor

I am a little confused when should i use heat sink or not using it.
For example if i want to design power amplifier or control servo motor and i use power transistor, and if transistor runs at IC = 1 A and VCE=10 V the power dissipation = 10 W . So how to know if that transistor needs heat sink or not ?
i need an example and steps to know if my design requires heat sink or not
Thank you

Dear andro
Hi
I think You should use heat sink for that , do you know why ? consider the temperature of a soldering gun ! it will be about 20W up to 40 watt for simple works !
Best Wishes
Goldsmith

You definitely need a heatsink for 10W.

There's a simple guide to choosing a heatsink here:

http://www.kpsec.freeuk.com/components/heatsink.htm

hi.I think the best way for know such this information is to read the data sheet.and another thing which is good to know is that its not necessary that all the time plug the heat sink on power transistor,you can make a pic of Copper on your board,and put the transistor on it instead of using heat sink.
regard
pesarirouni

Dear pesarirouni
Hi
I don't think , it is reasonable to eliminate that dissipation on copper of PCB ! that way will use for lower dissipations such as 2 watts!
Best Regards
Goldsmith

These will help you.....

Heat-Sink-Temperature-Calculator
http://www.daycounter.com/Calculators/Heat-Sink-Temperature-Calculator.phtml

ONLINE HEATSINK CALCULATOR
http://www.changpuak.ch/electronics/calc_23.php

An introduction to Heatsinks and Cooling
http://robots.freehostia.com/Heatsinks/Heatsinks.html

Thank you for your replay
But i want to know, is there any reference for using heatsink if the watts passed the margin? i mean if the watts for example 5 w or less how do i know i must attach heat sink any criteria for helping??
Thanks

But i want to know, is there any reference for using heatsink if the watts passed the margin?

Click to expand...

This reference is Tj ( Junction temperature in transistors)
The maximum temperature of transistors is normally 150°C, however, we recommend usage at less than 100°C.

You can calculate this by ---

Maximum allowed power dissipation
The junction temperature rises due to consumption of electrical power within the transistor and increases in ambient
temperature.
The maximum allowed power dissipation is the amount of power consumption needed to raise the
junction temperature to the maximum allowed rating.

PCMax. = (TjMax. − Ta) / (Rth (j − a))

TjMax. is the maximum allowed junction temperature,
Ta is the ambient temperature, and Rth (j − a) is a thermal
resistance where (j − a) includes all thermal resistance from the junction to the external air.
By using a heat sink for improved heat dissipation, the thermal resistance can be reduced and
allowed power dissipation improved.
Also, only DC allowed power dissipation is normally indicated. When a transistor is used for switching, the rating can
sometimes be exceeded. In the case of saturated switching, the transistor moves between the saturated region
and the cutoff region. In both regions power dissipation is low, and if the power dissipation of the transient state
which moves along the load curve can be ignored, it can sometimes be acceptable for the operating point to move
into the

VCE × IC > PCMax.

region provided the voltage and current ratings are not exceeded. The maximum allowed power dissipation has
been determined based on repeated reliability and damage tests, however, we recommend use at 75% of the rated
value.

Good reading ( read at least 3,4 and 5 )
Operation notes : Transistors
Rev.A 1/7
Selecting semiconductor devices
**broken link removed**

Example : Datasheet Power dissipation in BC639