Sorry to be the one to say this, but "It depends" . . . What are your goals? If the LV side of the circuit has to connect to some external signals, isolation is necessary. Opto-triacs are one nice way to do that (one of many). If there are no external connections, there should be no need for isolation. Specific example: we make triac-based lighting controllers used for outdoor decorative lighting. Standard, simple BTA40 triacs driven from a picket-fence type gate driver circuit. 4 channels of high power AC control driven from a 12c508 or 12f675 (depending on the model) and 4- 2n4403 transistors as gate drivers. Gate drive is 200mA pulses 6us wide @ 256us rep rate. Inexpensive, extremely reliable even low wattage loads (triacs stay turned ON even with a single 5W resistive load), operates down to -45C or colder. Many of these are controlled from external controllers. We use an inexpensive plastic fiber with matching transmitters and receivers from Industrial Fiber Optics. So: triacs, PIC, all supporting circuitry operate at line voltage. Communications is via plastic fiber. CSA and UL approvals. No problem. dwayne PS - if you *DO* drive these triacs directly from a PIC pin, make sure you check all conditions. Which quadrants are you firing in, how much gate drive is required in the worst quadrant at low temperatures, how much current do you actually get from the PIC pin at the temperature extremes. Me: I chose to use the least expensive triacs available with the voltage and current ratings I needed. I then threw in a few pennies of extra parts in a fairly unique configuration to give me the performance the application demanded. It was a worthwhile tradeoff. dwayne At 12:18 PM 12/19/2007, RV9 Factory wrote: >STMicro has a line of triacs (BTA16-600SW is one example) designed to be >driven directly by a microcontroller (or whatever) without using an >optoisiolator. > >Is this a safe and/or acceptable practice? Power to be switched is 120VAC >~8A -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist