Re: half-bridge MOSFET question
- From: "Paul E. Bennett" <peb@xxxxxxxxxxxxxxxxxx>
- Date: Sat, 18 Feb 2006 21:06:00 +0000
Mike wrote:
(This might be better suited to a different newsgroup, but I know the
embedded people know what they're doing ;)
I'm looking at half-bridge designs for 3-phase motor driving.
If I have the direction right, some of these designs use P-channel MOSFETs
on the top and N-channel MOSFETs on the bottom. However, I've also seen a
few that use N-channel MOSFETs for both the top and bottom.
Is this correct, and what are the advantages of one design over the other?
Thanks! -Mike G.
It is a shame that werty could not be a little more coherent in his response
(but I am aware that English may not be his first language).
Yes, most MOSFET or IGBT based three phase bridges will feature N-channel
devices more than the complementary pairings. This is because the N-channel
devices are often cheaper than the P-type complements but you also tend to
end up specifying the next device up the range as the complementary
P-channel devices will not handle quite as much current or power as the
N-channel devices. There are, of course, complications with an all N-type
design. You need to generate a voltage for the gate of the upper device
that will reach beyond the bridge supply rail (remember you need the
voltage between the gate and the source connections of the device and as
the source floats with the driven output voltage this can introduce matters
of gate drive isolation).
I either make a small multi-output switch mode power supply and use
opto-isolators to switch the gate voltage on to each device, or I expect a
pulsed gate drive signal and use that to drive the gate through a small
transformer.
IR <http://www.irf.com/> have a number of application notes that relate to
proper driving of MOSFET and IGBT's. These are well worth the read.
--
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Paul E. Bennett ....................<email://peb@xxxxxxxxxxxxxxxxxx>
Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
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