TRIAC Heat dissipation

[ENort.1]

Hi All,

 I have a circuit that works very well and uses the BTA24-800CWRG device housed in a TO-220 through-hole part. I currently have it bolted to a large enough heatsink and a fan above it just for safety and to keep it cool.

I am now updating the design and would like to miniaturize the circuit. I am looking at this ST part: T3035H-6G-TR. This is a surface mount version and I would prefer to use this instead of a large heatsink on the board.

I use the TRIAC in a pulse-skipping circuit to control a 120V 10A heating element. I developed a circuit to sense the zero cross and fire the TRIAC based on temperature and feedback through PID control. The TRIAC turns on during a percentage of multiples of the AC sine wave and stays on until the sine wave reaches the zero cross where the TRIAC turns off. Hard to explain but I hope you get the idea.

My question is, can I use a surface mount TRIAC for this particular application? Since it is essentially switching does the TRIAC generate that much heat while only conducting during a short period based on the percentage of the sine wave cycles? I do not know what the worst-case temperature would be for a 60 Hz sine wave and the surface mount TRIAC. Since it is a "switching" application and the TRIAC isn't ON 100% of the time I would figure the TRIAC wouldn't dissipate that much heat or am I wrong? Am I wrong to think that a surface-mounted TRIAC is a good idea? Can someone shed some light on this subject and let me know if I can use this part and what size copper area I need to dissipate the heat would be great. I can use a fan over the device if needed I just need some guidance so I can reliably run the circuit without destroying the TRIAC.

Thanks,

Eric Norton

[AScha.3 · Accepted solution]

Hi,

at 10A and maybe 1.5 V forward voltage the triac might produce 15W heat. This needs a lot of cooling.

So just calculate, how much on-time you have and you see, how much cooling needed.

And be aware: just the triac and not much copling to massive heatsink will heat up in some seconds.

So if your on-time is always 0.2 sec every 5 minutes, yes, can do it on smd.

But if your on-time more than some seconds...need heatsink.

[ENort.1]

Okay, thanks for this I appreciate it!