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| Design ideas for a low-count part, low power isolated DC-DC power supply? |
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| blackdog:
Hi Last year i needed a low noise low power power supply with 3 to 5 outputs. So i designed something that was not switching and it uses a small audio power IC in an Wienbridge configuration. This is a topic on a Duchs forum om mine, use Google translate if you wish. https://www.circuitsonline.net/forum/view/138876/1#highlight=voeding And this is the main schematic witch shows only two seperate outputs. Just for some inspiration... :) Kind regards, Bram |
| SiliconWizard:
Thanks for the additional ideas and the Royer converter. @ezalys: as nctnico suggested, using just flat coils on both sides of the PCB instead of a true transformer is much simpler and should work well enough with resonant coupling. Would not require a minimal PCB thickness. If coils directly as PCB traces, as I further suggested, give a decent efficiency, it would really be a low-cost and low part count solution. I like the idea. One additional benefit of using resonant coupling is that you can get waveforms close to sine waves if your Q factor is decent, which yields way better results in terms of EMI than flyback converters. This is also what you get with blackdog's solution, but the quiescent current would certainly be much higher. |
| T3sl4co1l:
The smallest/cheapest DC-DC converters are just multivibrators with a transformer hanging off it. No protection, no control, only raw AC. They tend not to go into this aspect in much detail, in the datasheets, but it is apparent from the characteristics they must provide (e.g., output regulation is sloppy and PSRR is nil). You'll find circuits can in fact be simpler, but even more compromises must be made. This is the basic plan of the blocking oscillator. The transistor turns on hard, due to positive feedback, then turns off due to rising inductor current and/or falling base current (due to the relatively small value of Cbb, which discharges through Rb); in either case, hFE rising until it comes out of saturation. When it switches off, the voltage flies back, where you employ a clamp diode on the collector (for a boost or SEPIC converter) or secondary (for an isolated flyback supply). Like the Royer, a feedback winding is needed, which itself may be more expensive (i.e., custom magnetics) than throwing a few more transistors at it (especially transistors with nearly zero incremental cost, i.e., on an IC). Discrete circuits are entertaining, but do not fool yourself into thinking they are in any way size- or cost-effective except in very rare cases today. :) (I'd say, the case of making a million qty run is rare enough to count.) Tim |
| schmitt trigger:
--- Quote from: Wolfgang on November 07, 2018, 04:32:21 pm --- I used old ISDN transformers for my low-noise converters and some energy harversting experiments, also employing Royer converters: electronicprojectsforfun.wordpress.com/energy-harvesting/ --- End quote --- Very interesting comparison! Thanks for sharing. You comment that a low drop rectifier is mandatory, is absolutely correct to extract the last millivolt. Do you think synchronous rectification would significantly help here? I understand that the circuit's complexity would increase, and thus this suggestion may be only a brain-fart. |
| Wolfgang:
--- Quote from: schmitt trigger on November 07, 2018, 08:58:39 pm --- --- Quote from: Wolfgang on November 07, 2018, 04:32:21 pm --- I used old ISDN transformers for my low-noise converters and some energy harversting experiments, also employing Royer converters: electronicprojectsforfun.wordpress.com/energy-harvesting/ --- End quote --- Very interesting comparison! Thanks for sharing. You comment that a low drop rectifier is mandatory, is absolutely correct to extract the last millivolt. Do you think synchronous rectification would significantly help here? I understand that the circuit's complexity would increase, and thus this suggestion may be only a brain-fart. --- End quote --- Sync rectification could help, thats correct. There was some IC that did it very elegantly LT4320 but this does it to 600Hz only. Maybe there is a faster part just as simple ? |
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