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Trying a selection of different diode types in a buck converter and measuring efficiency.
Trying a selection of different diode types in a buck converter and measuring efficiency.
By Julian
Youtuber, shed dweller, solar charge controller aficionado
Great Sir.
is it just me or is Julian giving us the finger when he points!
There is one thing you missed. The schottky diode switches a lot faster. I guess your switching frequency is a lot lower than most SMPS. That's why schottky is not much different than normal rectifier. But once you get to a bit higher frequencies – let's say 50 kHz (which is still relatively low), a regular diode won't be able to do the job. I've tried it at 100 kHz – it just doesn't work.
Now try putting 3 schottky diodes in parallel, not to greatly increase "safe" current capacity but instead, lower forward drop at any current that's a significant % of the diode rating, since ultimately the diode rating depends on the heat generated in that package size, which is based upon the forward drop at that voltage (and of course, heatsinking in a package that allows for it. Purists would hate the idea of 3 diodes in series but stop to consider how inexpensive a bag of diodes is these day and how precious efficiency can be on battery or solar power.
I would suspect that the body diode of the MOSFET is a little bit better than the discrete diode because of their difference in voltage threshold AND in their recovery time (the time for which the diode still conduct while freshly moved into reversed bias, which can reach the milli-second). A discrete silicon diode has a slower recovery time than the body diode and itself, lower than a Schottky. If the power is too high for a Schottky, it is recommended by the literature to use SiC (Silicon-Carbide) diode.
You should check also a fast switching silicium diode (1N914, 1N4148) versus a rectifier silicium diode (1N400x), there should be a noticeable difference, with a better efficiency for the 1N914.
I'd find it useful if you could briefly summarize what you've got set up and what you're trying to do with it at the beginning. Sometimes in the process of trying to work out what everything is, I miss relevant portions of the presentation.
Why don't you draw lines on the wood between the (closer) terminal posts that are interconnected?
With no diode you probably damaged your MOSFET.
have u checked out "interleaved" buck/boost converters? that was the magic search term for me when i was building my solar mppt circuit
Another thing to consider with diode choice is the reverse recovery time. If you're switching at 100kHz+ then some jellybean diodes may end up conducting the wrong way for a significant part of the switching cycle. Schottky diodes are normally quite fast in addition to the lower forward voltage. They're not perfect though, schottkies have a lower max blocking voltage (normally ~40V) and can have a few mA of reverse current when blocking.
Why not use another MOSFET as a rectifier? Not the body diode, the actual MOSFET. You have a floating gate driver, it'll work. Great efficiency, too.
Julian, for the sake of clarity would you add some black, Sharpie, lines on your breadboard between the connected, binding posts. Maybe it's just me, but I had to repeatedly think about what binding posts were connected during your explanation. Otherwise, I am enjoying your explanation of buck / boost conversion. Cheers.