Need help on Dimmer design

[Nicholas]

Hi,all
I m designning a dimmer for both resistive and inductive loads using TRIAC.
I know special concern should be take while dimming inductive load. But what shall I do in my circuits? Is there any detailed sample I can take for reference?

On epanorama.net, I found this words:
"Special dimmers which have a separate controlling electronics connected to both live and neutral wire and then the triac which controls the current to the load usually work much bettter with inductive loads."

Is there any circuit for reference?

Thanks in advance.
Nicholas

 

[IanP]

With inductive loads you will need so called "hard firing technique"

However with an inductive
load the current ’lags‘ behind the voltage so it is
possible that the current through the triac will not reach
the triacs threshold level before the trigger pulse ends.
This results in unacceptable dimming performance. To
avoid this, dimmers designed for use with wire wound
transformer fed loads use what is known as a hard
firing technique. This ensures that the trigger pulse is
maintained for a long enough period of time to ensure
that the current reaches the device’s threshold level.

Example of a circuit using this technique here:
http://www.scopeboy.com/tesla/ol2psu.html

 

[Nicholas]

Thank you. BTW, any circuits about doing phase control using MOSFET? There is an DI on EDN 5/21/98. But the figure can not be located now.

Thanks
Nicholas

 

[IanP]

I don't think you can employ MOSFETs in AC applications for phase control ..
These area is covered by SCRs and TRIACs ..