There are several companies that make the same 1/32 brick power supply with planar transformers. I'm sure there is a appnote/cookbook or reference designs on the design of these small supplies but I can't find them.
In my application I cant use the commercial parts as the parts are not rugged enough so we'd like to build a custom one.
Anyone know of a public domain reference design or appnote on making these?
Thanks.
I couldn't qualify these for consumer apps, at the advertised ratings, based simply on their own thermal imaging.
What do you mean by rugged enough?
At these power densities, even the 'experts' trip over their own salesmen.
RL
Cool. First time I used planar transformers, I got about 10W through a transformer the whole size of that module. Helps to use more than two layers, of course. They're really pushing it, and getting only 75C temp rise for that much power density isn't bad.
If they're getting too hot (as legg observes), they should run a hell of a lot cooler with derating. They appear to be ceramic capacitor construction, so they should have fine lifetime at reasonable temperatures.
Planar transformer design works like any other kind, helps to have a PCB editor that supports and facilitates their design of course.
Tim
-- Deep Friar: a very philosophical monk. Website:
One of the issues is isolation - the insulator temperature index being limited to that of the printed wiring means there are certification issues.
Others involve PTC of loss in ferrites (above ~85C) and fets (always). I'd want to see two timestamped images that didn't vary appreciably.
It doesn't matter for the supply itself, if it runs cooler when derated. It would allow use in a specific product, where suitably derated - but thats not what you pay for in a pre-qualified subassembly.
I expect that any certifications may specify an airflow, but I've never done this with products that didn't generate their own.... Sticky issue.
RL
I'm mainly interested in what these designs look like in the inside so I can get an idea of how they get them so small. Our current rugedized constructed power supply module is 10X bigger. I'd like to see if there are any tricks they are using beside pushing components to the ragged edge to make the supply smaller. even at 5X this size it would be a substantial improvement in our present one.
Rolling your own is a decision that has to be justified, in the first place. If you can't beat them, the alternative is to use their product. High reliability situations may even preclude the use of a single converter. Like I said - define ruggedness.
Can you stick to telecom bus dc inputs? Safety agencies recognize these as being isolated, so that only basic isolation is required for SELV at the system output. This may not be important for printed transformer winding use, but that use is a decision that needn't be predetermined.
Second consideration is topology selection for magnetics and silicon utilization, over the functional operating range. Unless you have bright ideas, you're going to be using two magnetic components, with the isolation transformer operating under reversing flux levels. You may be able to get away with murder at lower power levels, but the closer you get to competitive power densities, the less room there is for the 'big semi - small heatsink' solution.
The single transformer employment in your OP showed an attempt at resonant transfer, judging from the output ripple waveforms. This may have worked fine for higher output voltages and lower turns ratios, but you could see the results of trying to stretch it to low output voltages and higher output currents.
Switched snubbing and synchronous rectification are the most common methods of reducing size of the parts used, even for single-magnetics type flybacks, in spite of their potential complexity. These can be stretched and massaged for the application. There's a plethora of literature out there covering component selection for those circuits.
RL
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