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Triac clearance,creepage and track width

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toninlg

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triac soldering temperature 220vac

Hi,

I have to do a PCB with a triac (TO-220 isolated package) and an heatsink.
The maximum current is 9A. I've found tables for the track width but how can I choose the tolerated temperature rise in order to calculate the dimensions of tracks?

I've seen a table with clearance distances (**broken link removed**), with 220VAC it seems that clearance should be 1.50mm. With the required diameter for the (elongated) pad (regarding the pin diameter), the distance between the pads is less than 1mm and less than 0.9mm between the pads and the heatsink. So, what can I do in order to respect clearance distances?


Thank you.
 

creepage clearance

As you posted the question in the "Professional Hardware" forum, I assume that a PCB coating is intended anyway. This would solve the issue.

Furthermore, according to IEC 1010 creepance distance rules, 0.7 mm would be O.K. if at leat the board is coated by solder resist.
Because the triac is self-triggered in case of overvoltages, no overvoltage category must be considered between triac
terminals. You also mentioned "to-heatsink" creepance distance. Depending on the heatsink potential, different requirements
may apply here, e.g. reinforced insulation.
 

on creepage and clearance

Is 0.7mm for clearance, for creepage or for both?
There is a solder resist, but no conformal coating.
Must the distance from pad to pad be greater than 0.7mm since there is no solder resist on the pad?
The heatsink is a vertical one soldered to the PCB and has no electrical connection. The triac is a TO-220 isolated package.

Thank you.
 

pad-to-pad creepage

Hi there,

A common practice is to stagger the centre leg. This increases the creepage distance and also makes it easier to connect large tracks to the pads.

Another option is to use a conformal coating.

Hope this helps.
 

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