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Triac track width and clearance advices?

autodeskguest

Hi,

 

I�m making the layout for a PCB that uses a triac in TO-220 package. The maximum current in the triac (BTA312Y) is 8 Amp. and the copper thickness 35�m (1 oz/ft2). What track width would you recommend? I�ve seen calculators on the Internet but they ask the allowable temperature rise and I don�t know what value I can choose. On the other hand, I�ve seen that IPC recommends 220mil for 8 Amp., 10�C rise and 1oz/ft2 Cu but it�s very big?

 

What value do you use for track clearance for 220V mains voltages?  I�ve seen 0.75mm (http://www.electronics-project-design.com/PCB-Design.html ) for coated board. But here (http://www.smpspowersupply.com/ipc2221pcbclearance.html ) the values are not the same and I don�t know what to use? Is bare board for PCB without parts on it? So do I have to use assembly and �external components leads, uncoated� if : the board has a solder resist mask, is populated and if there is no coating on component leads?

Is the clearance also needed between the component�s pads (external diameter to external diameter)? If so, is it possible with a standard TO-220 package?

 

 

Thank you.

 

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Parents

  • a track larger than the pad is not a problem, the pad may get somewhat

    hotter than the rest of the track but it's small and attached to a big

    track and big component lead that will be most likely hotter than it is.

      the big track improves heat sinking, this only becomes a drawback if

    it makes soldering the pad difficult, that's why a polygon will generate

    a thermal isolation around the pad.

     

    an 8 amp triac when on will generate about 8 watts, that's a big waste,

    consider using some arrangements of low Ron MOSFETS or optical relays to

    perform the same task with /way/ less heat. triacs also trigger

    unpredictably on inductive line transients, in my experience. you need

    to test for this, a good test is to plug in a vacuum cleaner on same

    outlet as the DUT and turn it off and see if you don't get transient

    conduction in the triac, bet you will image

     

    the covered and uncovered specs for track temperature rise refer to the

    presence of solder mask which increases heat rise in a trace.

     

    as for isolation, at atmospheric pressure, you don't need much, at low

    pressures, 5V will produce corona discharge. route your 220V traces with

    user safety (fingers, tools, scope probes) in mind. i would make them

    covered with solder mask. to find the minimum clearance, you need to

    look up the dielectric strength of air at your ambient temp and

    pressure. use the peak voltage of the AC wave. you shouldn't have any

    trouble giving yourself a generous safety factor at normal air pressures.

     

    that enough advice for ya? image

     

Reply

  • a track larger than the pad is not a problem, the pad may get somewhat

    hotter than the rest of the track but it's small and attached to a big

    track and big component lead that will be most likely hotter than it is.

      the big track improves heat sinking, this only becomes a drawback if

    it makes soldering the pad difficult, that's why a polygon will generate

    a thermal isolation around the pad.

     

    an 8 amp triac when on will generate about 8 watts, that's a big waste,

    consider using some arrangements of low Ron MOSFETS or optical relays to

    perform the same task with /way/ less heat. triacs also trigger

    unpredictably on inductive line transients, in my experience. you need

    to test for this, a good test is to plug in a vacuum cleaner on same

    outlet as the DUT and turn it off and see if you don't get transient

    conduction in the triac, bet you will image

     

    the covered and uncovered specs for track temperature rise refer to the

    presence of solder mask which increases heat rise in a trace.

     

    as for isolation, at atmospheric pressure, you don't need much, at low

    pressures, 5V will produce corona discharge. route your 220V traces with

    user safety (fingers, tools, scope probes) in mind. i would make them

    covered with solder mask. to find the minimum clearance, you need to

    look up the dielectric strength of air at your ambient temp and

    pressure. use the peak voltage of the AC wave. you shouldn't have any

    trouble giving yourself a generous safety factor at normal air pressures.

     

    that enough advice for ya? image

     

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