| Electronics > Projects, Designs, and Technical Stuff |
| Analog challenge exercise |
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| T3sl4co1l:
...Which, for those who haven't seen it, and also, I update from time to time: https://imgur.com/gallery/M1S0DbI Tim |
| SilverSolder:
I have seen the single transistor circuit in actual made-in-China 5v wall wart supplies... They worked OK up to about 100mA... |
| SilverSolder:
--- Quote from: blueskull on February 08, 2020, 04:42:29 am --- --- Quote from: SilverSolder on February 08, 2020, 01:19:45 am --- I have seen the single transistor circuit in actual made-in-China 5v wall wart supplies... They worked OK up to about 100mA... --- End quote --- Depending on the transistor, a genuine or well made clone of MJE13003 should be good for 500mA 12V or 1A 5V. --- End quote --- I tested it, it couldn't do more than about 100mA before the voltage had dropped below the USB spec. The transistor in the device I tested was something very ordinary, in a TO-92 plastic case... I was impressed that it worked at all, let alone supplied 100mA! To me, an engineer that does a lot with a little, has magic and genius in him. |
| SilverSolder:
--- Quote from: blueskull on February 08, 2020, 01:45:55 pm --- --- Quote from: SilverSolder on February 08, 2020, 12:35:06 pm ---I was impressed that it worked at all, let alone supplied 100mA! To me, an engineer that does a lot with a little, has magic and genius in him. --- End quote --- Yours probably doesn't have an optocoupler feedback. It depends on auxiliary winding to sense secondary voltage, which is prone to large droop. A properly designed self oscillating BJT flyback should be good for at least 100W if efficiency is not the most important factor. Most metal box "industrial SMPS" you get from China are based on self oscillating BJT flyback. --- End quote --- Mine did not have an optocoupler feedback. I did trace the circuit and I think you are right, it did use a winding on the transformer for feedback. It was built down to the absolute minimum cost with as few parts as possible... which was not many parts at all! |
| Yansi:
--- Quote from: blueskull on February 08, 2020, 01:45:55 pm --- --- Quote from: SilverSolder on February 08, 2020, 12:35:06 pm ---I was impressed that it worked at all, let alone supplied 100mA! To me, an engineer that does a lot with a little, has magic and genius in him. --- End quote --- Yours probably doesn't have an optocoupler feedback. It depends on auxiliary winding to sense secondary voltage, which is prone to large droop. A properly designed self oscillating BJT flyback should be good for at least 100W if efficiency is not the most important factor. Most metal box "industrial SMPS" you get from China are based on self oscillating BJT flyback. --- End quote --- Nope they aren't. They are halfbridges and not self oscillating. (typically, the good ole mother 494). Maybe just the small metal case ones up to some 20 30W or what. (Never seen one with flyback yet, neither did I have a small one under 100W in my hands). |
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