Need Assistance with design of bec

[eduardosousa]

Hi every one,
i am tray to do a bec, bateri eliminator circuit, i need to have 6v with no drop or very low 0,5v max at 3A (mast be stable and i cant autput more than 6V ) and low heat (cant use large heat sink) , i was traing to do with an 7806 but the drop it was +- 1v and it heat a lot, the input its 12v dc 53A,

the idea its to input 6v to a receiver for an radio controlled model.
but i have a little space to put it do i need the IC to be low heat emitter so i can not use heat sink or use a very little one.

i have try it with an 2n3055 , to

if any one have any idea of a god ic to use please

thanks
e.s.

 

[Papabravo]

Can't be done. Do the math.

(12V - 6V)* 3A = 18 Watts

Look up the thermal resistance for a TO-220 package to ambient. It should be in the neighborhodd of 60 degrees C per watt. The maximum junction temp of 150 degrees c will be reached pretty quick without a heatsink.

You'll do better with the TO-3 package, but you'll still need a heatsink.

It is a really tough order for a linear regulator without a heatsink.

 

[SMUGangsta]

would it be possiible to dump some of the excess voltage through a couple of power resistors before the regulator to spread the heating effect?

Although i just looked at some of mine, and they are about 20x9x9mm and only rated at 4Watts

 

[audioguru]

The receiver for a model draws far less than 3A. Maybe only 20mA.
Then the dissipation in the regulator is only 120mw and it will barely be warm.

 

[jpanhalt]

For high powered BEC's, almost every commercial supplier is using a switcher. Consider something like National's Simple Switcher regulators.

John

 

[eduardosousa]

I and thanks for the hellp ppl

"National's Simple Switcher regulators"

cod be the solution i will tray it. LM22679 i think it will do the job


"audioguru"
"The receiver for a model draws far less than 3A. Maybe only 20mA.
Then the dissipation in the regulator is only 120mw and it will barely be warm."

ok that´s right but wen i put 4 digital servos + 1 gyro all working like in a normal 3D figure, i have 2.4A and the current drop to 4,7V

 

[jpanhalt]

Have you seen the Castle (**broken link removed**) switching BEC's? A small group of us have been using them with good success. I spoke with an engineer there awhile back. He commented that one of the biggest problems they had to overcome was radio interference. I suspect you might be on the gigahertz equipment, but at least it is something to think about. The price is certainly right for something that is small and works well.

John

 

[eduardosousa]

hi jpanhalt, i am on 35mhz , it´s a god idea but i like to do my one electronics gadgets, its like a hobby, i have 1 working with an mje3055 npn transistor it work ok but heat´s a lot and on my 450 heli the problem its the space on a big one no problems it have a lot of space for a cooler
this was the test with 7808 and 7806 to have 2 out puts 1 with 5,5 for gyro and digital servo and other with 6v for tx and 3 head servos.

**broken link removed**

 

[jpanhalt]

The linear regulators won't cause a problem. It is the switching regulators that can interfere. The Castle engineer basically said that their first switcher design interfered with anything within 3 feet.

John

 

[eduardosousa]

ok the switching frec. cod be a big problem i nead to think on that

 

[jpanhalt]

I am a life-long modeler and fly mostly high-performance sailplanes. I am also an electronics hobbyist, but when it came to the BEC, and I thought about the problems, including the harmonics, the decision was made for me.

Good luck. John