Is a heat sink a good idea for 7805 voltage converter?

[hal keiner]

I am planning my replacement of the OEM Pioneer 6-disk CD changer with an Alpine 9886 head unit on my 2002 ST. In reading several posts on the excellent forum, I see that a 7805 voltage transister/regulator is suggested to eliminate the "pop" in the factory subwoofer when the head unit is turned on (see link below). I plan to follow this advice. However, in further researching the use of the generic 7805 voltage transister in other applications, it is suggested to use a heat sink with the transister.



My questions is this, is such a heat sink a good idea for this type installation? I already presume that it is not absolutely necessary, as it is not mentioned in the below linked thread. However, if it is a good idea for the long term life of the transister and/or subwoofer amp, then I would go ahead and install a heat sink with the transister. The replacement cost of the transister is not the issue but rather the trouble of replacing it if it were to fail often.



Thanks in advance for any input on this.





http://www.mysporttrac.com/shared/msgboard9e.asp?BOARDNAME=MSG&VIEW=1110014

 

[Thomas Rogers]

Yup, it's a great idea. Those voltage regulators run hot.



TJR

 

[Ryan Schaecher]

It's a pretty simple thing.... A 7805 will output 5V no matter what the input voltage is. The remaining voltage has to go somewhere.... it become heat through the internal resistance and the current draw of the device.



12V - 5V = 7V



I don't know what the draw is on the sub, but if it's say 100W, then the current draw is around 20A (100W/5V = 20A)



You will be generating around 140W (7V * 20A = 140W) in heat. More than a standard incandesent light bulb. Heat sink is HIGHLY recommended.

 

[hal keiner]

Thanks for the quick reply. I didn't realize that 140W of heat would be generated by that tiny 7805 transister. That is a lot of heat to be radiating out from under the dash. I'm going to go ahead an install the heat sink. One only costs a few bucks and it does not take up a lot of room.

 

[Thomas Rogers]

hkeiner,



You keep saying transistor. It isn't a transistor. It's a voltage regulator. It steps down a voltage to a maximum, in your case 5 volts. Think of it as a mini transformer. As R Shek said, the step down causes heat which has to go somewhere.



TJR

 

[hal keiner]

Thanks for the clarifiation. I knew that it regulated voltage but mistakingly thought it could also be refered to a transistor. Instead, I should have called it a voltage regulator, doo-dad, or thing-a-ma-jig. My bad. I don't know too much about electronic component terminology. :wacko:

 

[hal keiner]

duplicate

 

[Thomas Rogers]

No problem hkeiner.



Luckily you said "7805" so I knew exactly what you were talking about from my college days and "Electronic Devices"



TJR