digital dimmer

[roo7flat5]

http://www.onsemi.com/pub/Collateral/AND8011-D.PDF
Would someone knowledgeable please answer a few questions on this
circuit?..
What is the function of the variable resistor, 10kohms, -ve,Lm339?
What would be a suitable transistor?
Any help greatly appreciated.

 

[Phil Allison]

"roo7flat5"

http://www.onsemi.com/pub/Collateral/AND8011-D.PDF

Would someone knowledgeable please answer a few questions on this
circuit?..

What is the function of the variable resistor, 10kohms, -ve,Lm339?

** It sets the timing point for the comparator - it is meant to be at
exactly the same time as the AC voltage zero crossing. However, since there
is a small and unpredictable phase shift in the 12 volt transformer ( due to
primary magnetising current) a correction is needed.

What would be a suitable transistor?

** BC547 etc.



............. Phil

 

[roo7flat5]

Thanks for your input.

Phil Allison wrote in message
<3fa87719$0$3792$afc38c87@news.optusnet.com.au>...

"roo7flat5"

http://www.onsemi.com/pub/Collateral/AND8011-D.PDF

Would someone knowledgeable please answer a few questions on this
circuit?..

What is the function of the variable resistor, 10kohms, -ve,Lm339?


** It sets the timing point for the comparator - it is meant to be at
exactly the same time as the AC voltage zero crossing. However, since
there
is a small and unpredictable phase shift in the 12 volt transformer ( due
to
primary magnetising current) a correction is needed.


What would be a suitable transistor?


** BC547 etc.



............ Phil