# High current triac control, pcb trace & heat

I need to drive 30A 380VAC signal with phase control using triac BTA41-600BRG.

BTA41 specifications seems enough but a confusing point is thermal and PCB trace width consideration.

According to online pcb width calculators, 31A current need so much thick traces which is not normal pcb design.

So BTA41 is not good to use in pcb boards with such power, am i wrong?

Should I use BTA40, or is there any way to use BTA41 in circuit with high power (31A, 380V) load, without thermal problem?

• Anything in that package (TOP3) is intended for PCB use. But you're right - not "normal pcb design". Of course, "normal" doesn't run 30 amps, either, so that's not a paradox. Whether you use the BTA40 or BTA41 is up to you, and depends on how comfortable you are with the currents, and what else you're doing with it. For instance, integrating the BTA41 on a pcb with the driver and monitoring circuitry will make a more compact, integrated assembly than using an external BTA40 with a wiring harness. It's up to you. – WhatRoughBeast Jun 9 '17 at 14:11
• 30A is a must for the project, compact design would be better but... I have to use BTA40 Thanks for answer. – mayhan Jun 9 '17 at 14:17
• "but..." But what? If you can produce the trace widths your calculator calls for, there is no problem. And be aware that most pcb houses will allow you to specify 2 ounce copper for thicker traces. If you're rolling your own, you can solder copper wire to your traces to increase capacity. – WhatRoughBeast Jun 9 '17 at 14:20
• circuitcalculator.com/wordpress/2006/01/31/… calculation shows ~50mm width. Is it not weird? – mayhan Jun 9 '17 at 14:23
• What is the point of your comment? Why do you show a calculation for 10 amps when you are concerned with 30? What does "calculation shows" mean? Stop hinting and start communicating. No one can help you if you won't speak plainly. – WhatRoughBeast Jun 9 '17 at 14:26

The very large copper lines calculated are normal for such a current need. But if I were you I would check that the load is affectively 30A RMS in permanent mode or in transient (inrush) mode. It could make a big difference in the size of your copper lines and triac heatsink.

Moreover, I see two problems with your choice of device : thermal and voltage.

THERMAL ISSUE

30A is a very very heavy load for a triac. I hope you have the biggest heatsink ever. If I am not wrong, the BTA41-600BRG is a STMicro device. They have a good thermal design notice[1].

According to this notice, you would need a heatsink of at least 1°C/W. Such a heatsink is 120x120x40mm and more expensive than the triac itself!

VOLTAGE

The BTA41-600BRG is a 600V triac in permanent mode.

When you control a 380VAC (I assume it is a tri-phase), then you need to take in account the peak value of the voltage, i.e. +15% to take in account international standard on AC lines and a sqrt(2) factor.

$$V_{peak} = 380 \times 1.15 \times \sqrt{2} = 618 V > 600V$$

Therefore I would recommend that you select at least a 800V triac.

• Thank you. I will consider your advices. After a few trial and error, I will share the results. Hope to turn soon. – mayhan Jun 12 '17 at 10:19
• Did you get to make it work? – ARB Jul 15 '17 at 18:38