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Temperature Control in Small Electronic Circuits

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quicksilver

Wed Jul 09 2008, 07:18PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

My query deals with temperature control on electronic components within a small space. Ideally I would use a fan but in small boxes that are mostly sealed the small fan [that would fit] would be a computer CPU fan and this could entail additional circuit design to allow for a much lower controlled voltage, specifically for the fan. Whatâ€™s more Iâ€™m not sure if that would even be worth the additional work.
In a small project that entails the use of a heat sink (a Mazilli driver within a closed box for instance) I was considering the use of â€œpink housing insulationâ€ in addition to a proper heat sink. My reasoning is that insulation of this type is used for keeping BOTH heat and cold from â€œwanderingâ€ within a closed environment. What I have noticed is that a heat sink dissipates the heat from the semi-conductors but in a closed environment allows everything within to heat as well.
I would like to hear some opinions on the methods used in small sealed platforms like a power supply, etc. And if insulation may make a positive differenceâ€¦.? Additionally, any other ideas to lower temperature or keep heat from enveloping a small enclosed project.

Proud Mary

Wed Jul 09 2008, 07:51PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The heat sink must be mounted outside the box, or form one of its sides, such as the top, where air can convect through its vanes.

Ken M.

Wed Jul 09 2008, 08:29PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Housing insulation only helps in houses because of an internal heating and cooling system, think of it this way if u took a box whatever size and sat it out on a cold day the inside and out side would be cold, if u did it ojn a hot day, both would be hot, now say you add the insulation, you might keep the box say 5c warmer but on the hot day the box would be even hotter, since the purpose of that insulation is to trap tempurates inside and reduce the effect of temps outside, hence like HArry Said you would need to mount the fins on the outside.

quicksilver

Wed Jul 09 2008, 09:50PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Indeed, Harry's point about convection is paramount. I was looking for a work-a-round for situations where the heat sink is just that small that out-board mounting (& often what parts I have to work with) become a task out "using the old router" to achieve a rectangular opening. I put together a little 3a 20Vdc supply and the heat sink was just that annoying size: to small to be out-boarded and large enough to possibly heat other passive components.

The "trapping" of heat or cold makes sense also. In the majority of situations this wouldn't even be an issue but I am beginning to believe that advanced design elements for IC components have temperature issues addressed but they generally have the design "from the ground up" to work with.

I'm also beginning to think that my transistors, etc should not becoming that hot if all things considered; the design of the circuit is a good one.

One of the best examples of this "caught in the middle" heat issue is a solid state microwave oven. The heat sink is a fair sized one and demands the fan designed within the oven to keep things cool. However that power supply could be a very fine HV supply as it's remarkably small and light compared to a MOT. The heat issue keeps me from exploiting it however as the casing size would need to incorporate a fan; defeating the size and weight savings.

Obviously, this is not a monumental issue but if there was something unique to cool HV circuitry, overall design could shrink. I really just making conversation as I think there are some damn creative people out there who may have thought about this with SMD components. However, from an engineering/consumer stand point, what has appeared to shrink has been low voltage items like phones & computers.

Proud Mary

Thu Jul 10 2008, 05:16AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

quicksilver wrote ...

Obviously, this is not a monumental issue but if there was something unique to cool HV circuitry, overall design could shrink. I really just making conversation as I think there are some damn creative people out there who may have thought about this with SMD components. However, from an engineering/consumer stand point, what has appeared to shrink has been low voltage items like phones & computers.

Perhaps this is because heat must be dissipated into a mass of something - whether a mass of metal, or a mass of air. What is more, the dissipation must be made to proceed at a given rate, so that thermal equilibrium is reached, and the temperature stabilizes, within an acceptable range of operating temperatures.

Invent the lossless dielectric, the non-thermal resistor, and the 100% efficient electronic switch, and we shall have no more need of heat sinks!

HV Enthusiast

Fri Jul 11 2008, 11:17AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

A heatsink inside an enclosed box does ABSOLUTELY NOTHING. The heat has nowhere to go, and once it reaches steady state, everything inside the enclosed area is at the same temperature.

Either have an internal fan circulating air, or mount the heatsink on the outside. Also, the insulation is the worst thing to do.

Actcually, the best thing to do in this case is to pot the entire box (assuming its a metal box) with a thermally loaded potting (thermally conductive). This would allow heat to flow to the outside of the box where it can be cooled.)

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