Maximizing Heat Dissipation in High-Power SMPS Design

[mheslep]

If you want to wind up an old large iron core, 60 Hz transformer based, non-switching power supply you can get by with a volt/amp meter. You can not build and diagnose a high power 50 KHz switching power supply without a scope, any more than you can hammer nails without a hammer. The goal was to learn about SMPS operation. Even if you happen on a properly designed core, with this try-something-and-fire-it-up,measure-nothing approach you'll learn no more about SMPS design than you would by rolling dice.

 

[Baluncore]

An optimised switching supply MUST be engineered, it cannot be built using Monte Carlo techniques. You do not have the necessary equipment to work safely and successfully on the development of a high voltage half-bridge supply. Without an isolated development platform you can't measure enough to know the actual situation. You also require a fast and accurate over-current trip circuit to protect the driver transistors.

Whenever you get anything working you increase the load until saturation of the transformer destroys the driver transistors and ancillary chips. Your blind and undisciplined approach guarantees repeated failure.

 

[Salvador]

Speaking in terms of one of the most popular music genres I would like to say this little update is "4 all U haterz and non-BELIEVERS" out there.

I did a bit of reinforcing on my PSU in the meantime I installed the psu board into the aluminum mainframe which is essentially the amplifier box also housing the amp channels etc.
Now I added quite a bit of heatsinking on various crucial elements, like the mains rectifier (actually got pretty damn hot when I was loading the psu with 1.2kW), connected the output rectifier heatsink to the aluminum chassis which I made out of aluminum for exactly the resons of heatsinking.made a heatsink contact from the mosfets to the chassis using double isolation (first isolator between mosfet and one heatsink then another layer of insulation between that aluminum pad and it's connection to the chassis to which everything is heatsinked.
I even took an old CPU aluminum heatsink and attached it to the transformer that got hot under heavy load and now it's only moderately warm even when I was driving a 1kW+ load on the output.I used some aluminum cooking foil as the "thermalpaste" to even out the surfaces between the transformer ferrite and the smooth cpu aluminum block.

My monster load is two old clothing irons connected in parallel , each rated for 1600watts mains 230 volts , they pose a resistance of about 20 ohms when hot to my psu output and doing some calculations I concluded that the psu supplied at its peak about 1.2KW into that load since the voltage was 155 volts approximately, when the load was connected.only a 10 volt drop from my usual 165 volts of DC output under lighter loads such as a water heating coil and a halogen 230w bulb in parallel.I'd say not bad.given that it's not regulated , since the feedback was causing me trouble with voltage swing and unstabillity I just disconnected the feedback IC and to my surpise the output is very steady it only fluctuates when the mains itslef sometimes fluctuates.but since i have pretty decent mains filter caps they kinda compensate for that.
those irons by the way were submerged into a metal can filled wth cold water and the water started to boil about a bit more than a minute after power on.also my mains cable from the wall socker got pretty warm I'd say during the heavy loading.even the lamps on the ceiling went a bit dim.
I'm no that goot with AC power comsumption calculations mabe one can estimate based n my output numbers the approximate power drawn from the wall socket ?
the output was 155 volts DC over about 20 ohms of resistance the maths on DC side give about 7.7 amps.Now I'm finishing my other transformer and will soon be putting that in and also heatsinking it to the chasis.I laready have the other half bridge mosfets installed and have the place for the second IC ir2110, a small question if I may , is it okay for one SG3525AN to drive two IR2110, they all share a common small psu.but anything other than that the IR2110 are separate only that they share one psu and the outputs from the SG3525 chip which are going to both the inputs of one and the other IR2110.
the half bridges themselves are separate units and will be driving separate amplifiers, one half bridge driving two channels that are also able to bridge mode.

The thing I have learned so far is that when designing an smps with considerable output power one needs to have heatsinking with quite some capacity, I mean everything heats up , even the mains rectifier , actually I'm surprised but of all the things giving me heat the switching mosfets are the coldest ones of them all.
I increased the frequency a bit over the specified 50khz and increased the deatime with my reostat so that might give my mosfets a better waveform to keep them cold.
Also even though I have done both of my transformers with double litz wire in parallel both for primary as for secondary i feel the litz wire couldbe even thicker and it would only help.
Also a larger transformer core than necessary or specified would't harm probably either, giving some extra headroom for temperature and saturation if it happens.