Sorry, I shot through the forest without describing the trees:

No, I am not gamiliar with IGBT. I meant logic level MOSFETs; the P-channel
(switching ON the HV Rail) can be switched with a low-going signal
referenced against the HV rail, and the N-channel (switching load to GND
rail) can be switched with a hi-going signal referenced against the GND rail.

Image the H-bridge, with two N-channel 400V logic-level switched devices as
the LOW side drivers; obviously, these can be driven directly from two PIC
pins. Two P-channel 400V logic level; devices are used as the HIGH side
drivers. But how do we get a logic level 250+V above GND? We use a
Photovoltaic Isolator. These LOOK like optoisolators but they generate a
small (8V) to be used as "logic drive" to the P-channels. SO, two more PIC
pins drive the inputs to these Photovoltaic Isolators. Look at Digikey
PN#PV11050N for a dual isolator in DIP8 package. I like opto techniques
because they are unlikely to cause problems until the PIC is running properly.

For safety, be SURE to place a fast-acting FUSE in the high-side line, and
(2) place a bidirectional transorber rated BELOW the MOSFET rated voltage
to prevent these babies from being killed by motor noise.

I haven't used these at 200+V, but I have used them at 30V ande they run
VERY well.

HINT: if you have to pulse-width modulate, do it on the LOW side only, the
optos are too slow for that task.

--Bob

I was gonna draw it up, but the CAD system is busy.



At 10:59 PM 8/31/2003 -0700, you wrote:
>Drive it with MOSFETS switched on/off with opto-isolators. They switch
>sorta slow, but will work fine for this. Use H11F1, its an internal FET,
>can handle the HV.
>
>--Bob
>
>At 12:37 AM 9/1/2003 -0400, you wrote:
>>Does anybody have any good information about high voltage H-bridges? (about
>>200V @ 4A)
>>
>>I was thinking about IGBT but I'm a little fuzzy about how to drive the high
>>side of the bridge.
>>
>>Thanks
>>-Denny
>>
>>--
>>http://www.piclist.com hint: The PICList is archived three different
>>ways.  See http://www.piclist.com/#archives for details.
>
>--------------
>Bob Axtell
>PIC Hardware & Firmware Dev
>Tucson, AZ
>1-512-219-2363
>
>--
>http://www.piclist.com hint: The PICList is archived three different
>ways.  See http://www.piclist.com/#archives for details.

--------------
Bob Axtell
PIC Hardware & Firmware Dev
Tucson, AZ
1-512-219-2363

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.