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D2PAK triac max current

**AccountRemovedPerUsersRequest**:

Hi. I noticed an existing thread about D2PAK cooling, but since this is not exactly that, I dare to create a new topic.

So, I am planning to use T25 triac in D2PAK. Am I missing something critical?

Tj max is 125C, so 25C ambient, the delta T is 100. Rth (j-a) is 45, so the max W is 2.2W.

The Rd is 16mR, so driving 4A it means 256mW. So... I should be more than safe using D2PAK with 1cm copper surface (=the default on the data sheet) on both PCB sides...

A

**Benta**:

Are you mixing Triac and MOSFET here? I don't understand your reference to 16 mR.

**AccountRemovedPerUsersRequest**:

Not mixing, but trying to calculate how safe I am to use D2PAK triac on 4A. Not sure if using the dynamic resistance in the formula is correct tho.

A

**floobydust**:

A triac generates roughly 1W of heat per ampere. I use this for roughly estimating cooling requirements, assuming full conduction angle.

It's not that far off, example ST TN1215 12A triac with Fig. 1, 4A average current gives 4.5W dissipation, which is an awful lot for a D2PAK. You would need more PCB copper area, and would not design to 125°C that is too hot and what happens if the unit is in 30°C ambient.

**langwadt**:

--- Quote from: Axel_sr on December 04, 2021, 06:10:48 pm ---Not mixing, but trying to calculate how safe I am to use D2PAK triac on 4A. Not sure if using the dynamic resistance in the formula is correct tho.

--- End quote ---

a triac is mostly a fixed voltage of ~1-2V

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