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SMPS for dormant tube audio amp project
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T3sl4co1l:
Ah, well then... uh, tile saw?  Belt or barrel sander?  Dremel I don't think is going to be any easier than your existing flap-wheel solution, too small and tedious...

If you already have saws or grinders, a grinding wheel will do the job, and maybe you can make a little jig to hold the work at a fixed distance.  Drip on water in such a way that it doesn't get into the motor or create a shock hazard, and that should be okay...

Carbide should be pretty okay, ferrite isn't as hard or as strong as glass.  Would be more worried I think that you need a setup to make it repeatable.

Or, heck, if you already have an X-Y table, and a Dremel or the like, that'd be pretty sweet...

Tim
MagicSmoker:

--- Quote from: T3sl4co1l on August 21, 2019, 06:15:55 pm ---...
Carbide should be pretty okay, ferrite isn't as hard or as strong as glass. 
...

--- End quote ---

The problem with using a carbide cutting tool on ferrite is that they are both very hard and very brittle, so both are liable to chip or even shatter when they come into contact. A diamond-coated rotary burr* either in a Dremel or chucked up in a drill press (with a cross-slide vise) or a mill works far better.

FWIW, ferrite is gapped commercially with a diamond abrasive wheel in a surface grinder, which isn't something even the above-average home shop is likely to have. The only cutting process I have ever seen used on ferrite is a waterjet with carborundum grit.


EDIT - like this: https://smile.amazon.com/Diamond-coated-Cylindrical-Grinding-Mounted/dp/B015PK0IK6/ref=sr_1_30?keywords=diamond+burr&qid=1566414296&s=gateway&sr=8-30
Circlotron:

--- Quote from: MagicSmoker on August 21, 2019, 04:33:54 pm ---
--- Quote from: GK on August 20, 2019, 07:37:59 am ---The low-side IGBT conducts in the forward direction when the load current drops below the peak ripple current of the inductor - it's there to ensure that the regulator always operates in continuous current mode and is how the control loop is made to operate entirely unperturbed right down to a load current of zero.
--- End quote ---

Yes, a synchronous buck operates in CCM over the entire load range, but current flows in the reverse direction through the low side switch during the freewheeling period, so you can't use an IGBT here. The circuit still works because of the co-pack diode, but you aren't actually getting any of the benefits (or downsides) of forced CCM.

--- End quote ---
Yeah, that's a really good point. The lower IGBT is only doing something useful in DCM - keeping pulse width sensible at low load *and* providing ZVS for the upper IGBT. In that situation the filter choke current is bi-directional. When you get to CCM the choke current is uni-directional and as you say, during the freewheel period the IGBT won't conduct in the reverse direction, only the co-pack diode does, with it's attendant voltage drop. A mosfet can conduct in both directions, and during the freewheel period it shunts current around it's own body diode. So mosfet is a much better solution.
GK:
Will you guys please read my second post in this thread
I forced ccm with the low side igbt entirely for the control properties  ; constant pwm d/c at all load currents

Circlotron:
Commenting in a forum can be a bit of a problem sometimes. I'm not criticizing your design, rather it's just a general comment for the sake of others reading that might not be totally up to speed on the finer points of switching regulators. No offense intended.
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