question about linear Vreg , heat generation. (also about hooking :D )

[settra]

hello. i am planning to power an arduino in my car, with a 5V voltage regulator. (i will be using a protective circuit before the Vreg , to protect from cars spikes)
my question is this. the heat generated by the vreg is (Vin-Vout)*I ? (in watts).

the problem is that the voltage regulator will work ALWAYS. it will never stop...
BUT the arduino want draw much power.. it will work something like this: for 3 days, it will be drawing about 10mA. some times on that 3 days, it will draw about 60mA. and some other times , about 30mA.

so the heat generation, want ever be big. but, since it will always be there, will a big heatsink, solve the heat problem?? or after some time, it will become overly heat? do i need to use a small fan to cool it down??
P.S1 (i can use a very big heat sink, and i can use a 2A Vreg, to generate less heat in small currents?)

P.S2 . what about the decoupling capacitors?? can someone shed a bit light on how to hook them, and what they are for?? thanks allot!!

 

[picbits]

Have you considered using a switch mode type supply for efficiency ? If you're dissipating 70+% of your regulation as heat, you could surely look at other alternatives ?

If you *must* use a linear regulator, look at one such as the MIC2951 from Micrel as they are designed for automotive applications (i.e. load dump, reverse connection etc).

Heat generated at 60ma with a 14.5v electrical system (normally 12.5-14v) would be 14.5 - 5 * 0.06 = 0.57 watts which means it may get a little warm. You might want to pop a small metal plate and some compound on the top just to give it a helping hand - when the interior of the car is at 40 - 50 degrees C on a hot day things can get a bit toasty.

 

[ronv]

Don't worry. Be happy! Vin maybe 14.6 minus Vout - 5 times current = .06 (60ma) is around 0.6 watts. No heat sink or just a small one needed if it is the TO220 package.
The capacitor on the input helps filter out the noise from the car and keeps the regulator stable by keeping the voltage steady when the load changes. The one on the output keeps the voltage stable until the regulator can react when the load changes. Keep them both close to the regulator.

 

[settra]

i dont want to use a switcher, becouse "efficiency" in terms of energy is not neccecery. i only care about the heat...
so you think that if i just add a big heat sink, the heat sink will be able to absorb the heat, (Rememebr. 60ma will not be the usall. 10 ma will). ? no need to coll the heatsink itself.. cool!!

thaanks for the capacitors!! what velues are typical??

 

[audioguru]

For only 0.6W a little heatsink on a linear 5V regulator that is in a TO-220 case will be fine.
The datasheet for the voltage regulator IC shows recommended input and output capacitors.

 

[settra]

ok cool. thanks allot!!

 

[MikeMl]

ok cool. thanks allot!!

Besides, if you need a heatsink, you have an infinite one: the car itself. Just bolt the linear regulator (using an appropriate isolating washer kit) to the metal...