Re: Sync rectification (was Re: Controller - Motor Match )

[Rich Rudman <rmanzan@tscnet.com>]

Rod.Hower@ametek.com wrote:
> 
> Just a few notes about diodes.
> Schottky diodes have a 0.5V or less drop.
> Plus, and most important is the soft reverse recovery of the Schottky.
> The MOSFET body diode has a crappy reverse recovery and should not be
> relied on.
> 
> I replaced a Schottky diode (150V, 150Amp rating) with an ultrafast 'soft'
> recovery diode rated at 200A and 150V.
> The reverse recovery was not nearly as good as the Schottky causing much
> higher voltage overshoot during switching.
> Unfortunately, the schottky is rated for lower voltages.  The highest
> voltage I have worked with is 200V and 200A.
> IR quit making these because the semiconductor yield was too low.
> 
> I think the next best thing coming out is the Silicon Carbide diode.
> Harris (intersil,,,Fairchild) is supposed to sample some in the next few
> weeks.
> These devices have a much lower voltage drop than any other diode and/or
> transistor.
> The biggest plus is the ultrasoft recovery - it is much less than the
> Schottky and exponentially less than a MOSFET body diode.
> The good news for the EV driver?  Controller power output per cubic inch
> (or centimeter) should increase as well as reliability.
> 
> Rod Hower
> W8RNH
> 
	Forget about Schottky, too low a voltage, and not available in the size
I need. Now for 48 volt work that maybe a good idea. Since I am doing AC
drives, I don't have freewheel diodes per say. Now a SCdiode co-packed
with a 200 volt 120 amp sub 10 milliohm Mosfet, and I would drool.

Rich Rudman
Manzanita Micro