Mains clearance in a TRIAC driver


Posted on Feb 7, 2014

A TRIAC driver board for use with my reflow toaster oven project, which means mains voltages. IPC-2221 says that U. S. mains voltages require 0. 4mm clearance if coated with solder mask. A few questions: Can I run overlapping tracks on both sides of the board I don`t know how thick the PCB is but it`s a standard, 2-layer FR4 PCB. Since the 200 mil `tracks` (fills, actually) running from the screw terminal to the


Mains clearance in a TRIAC driver
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TRIAC are sort of, erm, wide, they have to either overlap or taper at the ends. How much clearance do I need between the high-voltage section and the low-voltage section I`ve kept them at least as far apart as the opto-isolators are wide but I`m curious what the standards say. I haven`t finished checking clearances yet but any comments about the circuit or the PCB are welcome. The top of the schematic is the TRIAC driver of course, and the bottom is a zero-crossing detector. I`m especially curious whether I really need two capacitors and two resistors for the detector, I got that from a Fairchild app note but there weren`t any voltage or safety ratings in the example so I had to assume the worst. For the zero-cross detector you can use only a single resistor instead of two caps and two 1K resistors but you will need a high power rating resistor (10K/5W for 120V AC mains or 22K/7W for 240V AC). Thanks for the advice. The reason I`m not using a zero-crossing opto-TRIAC is that I want to PWM the output - the detector is for keeping the pulses in sync with the AC waveform while still allowing me to delay them to get the varying levels of power I want. I also opted not to use a snubber since the load is always purely resistive, and the connector is where it is because that big pink thing is a rather large heatsink :-) That said, I do intend to move it to the right-hand side in an attempt to squeeze this onto a smaller PCB. Why...




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