Jan-Erik wrote:
>
> Anyway, we still don't know *what* you
> are triggering :-)
>

I'm using an alternistor to trigger a transformer. The transformer
supplies the voltage to a 3-phase brushless motor. In normal mode
of operation, the alternistor is on for the full 180 degrees. The
phase angle is adjusted under certain conditions to reduce the motor
voltage. Main purpose is to limit the current to prevent the motor
from burning out. The motor draws 10A@36V under full load. Using linear
control on the secondary side would require significant heat sinking.

Yes, there are other (perhaps better) ways to do this. I am taking
over an existing design, and many design decisions were based on
product cost. Sound familiar? A buck on the secondary side was
considered, but cost analysis showed it was cheaper to use
phase control.

>> Well, that still needs to be fine-tuned, but initial calculations
>> indicate a conduction angle range between 120 and 180 degrees. That
>> means worst-case I would be firing 60 degrees from zero crossing.
>
> 60 deg *before* z-c, not ?
> Or 120 deg *after* z-c ?
> The 120-180 deg range are the *last* 60 deg of one half-cycle ?
>

I mean 60 degrees *after* zero crossing. That would give me a
conduction angle of 120 degrees. I will be firing anywhere from
continuously (180 degrees) to 60 degrees after zero crossing.

Phil Eisermann
Electronics Engineer
The Ridge Tool Company
(440)329-4680

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