Winston wrote:
Michael A. Terrell wrote:
"DoN. Nichols" wrote:
On 2009-05-08, Michael A. Terrell wrote:
wrote:
On Thu, 07 May 2009 18:21:54 -0800, "Paul Hovnanian P.E."
wrote:
[ ... ]
And there are two diodes in series.
And you sure as heck won't be pumping 115 volts into the battery!!!!!!
Here is the newer rectifiers for alternators.
http://www.ixyspower.com/images/technical_support/Application%20Notes%20By%20Topic/Automotive%20Applications/IXAN0018.pdf
Actually -- that is not a bridge rectifier to convert three
phase AC to DC, but rather a bridge of mosfets to convert DC to three
phase AC -- as in a VFD. (It will need more logic to drive the gates to
do it right, but that is at least a start.)
Not at all sure that the voltage ratings there have any bearing
on what would be found in an alternator. Instead, it is described as
being to drive things in the automobile which *need* three phase
The same circuit can be used as an active rectifier. It has the
advanage of a lower Vf, which reduces the heat generated in the
alternator housing. It also means that trying to use it as a straight
single phase rectifier won't work.
Three phase synchronous rectifier?
Very kewl idea!
But,
1) They appear to be using the MOSFET body diodes to do
~ 10% of the rectification rather than using them as
voltage clamps (protection devices). This appears odd.
2) Though the MOSFETs *are* bidirectional, they are shown
installed 'backwards' from conventional usage.
During power production, the drains are negative in relation
to the sources. Strange.
3) I didn't see the gate drive circuit for the MOSFETs.
I assume it includes a charge pump to keep the high side
MOSFETs saturated during peaks.
4) This is a bridge all right but it's really to be used as
a source of 3 phase power, not a rectifier. Look at it
that way and items 1 and 2 are non - issues because
the current would flow in the opposite direction.
What is shown in a data sheet is never the full schematic. they
always have errors, on purpose, to prevent a direct copy.
Synchronous rectifiers have been around since at least the '40s, in the
form of synchronous vibrators. More that one OEM mentions FET power
rectification in their automotive sections.
--
Don't *faff*, dear.
--
You can't have a sense of humor, if you have no sense!