So the last bit for me to solve on my motor controller is this pickle...
I would like it to run off of 6V-42V input (preferably 6V-50.4V). This is 2 cell LiPo batteries all the way up to 10 cell Lipo (12 cell A123) or 12cell Lipo(14cell A123).
Anyways, the catch is that I also need a 5V/18V supply for the logic and gate drive circuits. The 5V isn't too hard to do. Just a buck converter which barely meets the dropout requirements. But the 18V is quite a bit harder.
Now, it seems no SEPIC, buck-boost, or flyback can do that and meet the input voltage rang. It is looking like I have to get a buck converter to step it down to power all the logic and then split off some of the output to a boost converter to bring it up to 18V.
Now...I'm not sure how I should go about this. Because I could power the logic and 18V boost converter straight off of the buck supply but that might makes some noise for the logic and create bad frequency interactiosn between two cascaded switching converters (what might happen here exactly? I'm not sure).
Or I could add filtering to isolate the two loads from each other after the buck converter.
I don't think using a LDO to isolate the logic from the boost converter will work because the switching frequencies are too high and can't be supressed by any linear regulator. Plus it also means the buck will be operating in dropout on a loaded 2 cell Lipo battery (not necessarily a problem since I searched high and low and found a PFET 100% duty cycle capable buck converter) and I might be able to squeeze the buck and LDO dropout into the little headroom I have above 5V and the battery input.
I would like it to run off of 6V-42V input (preferably 6V-50.4V). This is 2 cell LiPo batteries all the way up to 10 cell Lipo (12 cell A123) or 12cell Lipo(14cell A123).
Anyways, the catch is that I also need a 5V/18V supply for the logic and gate drive circuits. The 5V isn't too hard to do. Just a buck converter which barely meets the dropout requirements. But the 18V is quite a bit harder.
Now, it seems no SEPIC, buck-boost, or flyback can do that and meet the input voltage rang. It is looking like I have to get a buck converter to step it down to power all the logic and then split off some of the output to a boost converter to bring it up to 18V.
Now...I'm not sure how I should go about this. Because I could power the logic and 18V boost converter straight off of the buck supply but that might makes some noise for the logic and create bad frequency interactiosn between two cascaded switching converters (what might happen here exactly? I'm not sure).
Or I could add filtering to isolate the two loads from each other after the buck converter.
I don't think using a LDO to isolate the logic from the boost converter will work because the switching frequencies are too high and can't be supressed by any linear regulator. Plus it also means the buck will be operating in dropout on a loaded 2 cell Lipo battery (not necessarily a problem since I searched high and low and found a PFET 100% duty cycle capable buck converter) and I might be able to squeeze the buck and LDO dropout into the little headroom I have above 5V and the battery input.