03-10-2017, 12:43 AM
I've designed a few high efficiency boost converters - there's one for nixies on my web site - layout and component choice must be right to get decent efficiency. The inductor should be 22uH and low DCR with suitable saturation current rating, the diode should be Schottky and have a very low Mttr (bearing in mind the 1.2MHz switch speed), the ceramic caps should be around 22uF and be X5R or X7R with low ESR. Then there are stipulations on the layout - very important.
I suspect that at this price point they simply used whatever they had. The datasheet for the chip is pretty clear on the requirements. It would be interesting to strip one of these boards to see what they used. (Mark?) I love the fake Bourne's trimpots (even using a Bourne's part number) and wonder whether the output capacitor is in the right place.
If the output voltage is set too low then the SMPS will simply not run, leaving a DC path through the inductor and diode to the output. No harm should occur - the output has no short-circuit protection, so watch maximum load - more than an amp or so and the diode &/or inductor may cook.
The ones that caught fire in the YouTube videos probably had the SOT23-6 round the wrong way - easy mistake to make with a tiny symmetrical chip - the chip, if it's in the right way round, is pretty tough and has current limiting to protect its FET as well as thermal shutdown.
You tend to get what you pay for with this stuff
I suspect that at this price point they simply used whatever they had. The datasheet for the chip is pretty clear on the requirements. It would be interesting to strip one of these boards to see what they used. (Mark?) I love the fake Bourne's trimpots (even using a Bourne's part number) and wonder whether the output capacitor is in the right place.
If the output voltage is set too low then the SMPS will simply not run, leaving a DC path through the inductor and diode to the output. No harm should occur - the output has no short-circuit protection, so watch maximum load - more than an amp or so and the diode &/or inductor may cook.
The ones that caught fire in the YouTube videos probably had the SOT23-6 round the wrong way - easy mistake to make with a tiny symmetrical chip - the chip, if it's in the right way round, is pretty tough and has current limiting to protect its FET as well as thermal shutdown.
You tend to get what you pay for with this stuff
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