Hey guys. I'm looking to design a circuit to control an AC heater. Specs are 240V, 20A (closer to 15A continuous). I was planning on using a triac design, which, I'm of the opinion of, is a fairly common design path for this type of application. However, parts availability is a problem right now that I'm sure most are aware of, and I can't wait half a year or more for parts. I found some nice D2Pak parts from ST that are stocked, but at the power levels I'm looking to run at, I won't be able to dissipate over 20W easily in a D2Pak.
This thread makes it painfully clear, getting 5W out of a D2Pak would take some careful planning and heatsinking.
So in light of part availability (no readily available TO-220's), I started wondering if it would make more sense to design a discrete SSR using FET's. This will be an ON-OFF design, so I will need to design a circuit to detect zero crossings, which shouldn't be an issue as there is already a micro in the design. However, after looking around for FET's, seems like this is going to get a lot more expensive. I was hoping to accomplish it without a heatsink, but to do that, I need FET's with really low RDSon, and they get pricey fast. I would be OK with paralleling multiple, it the cost wasn't ridiculous, especially if it meant getting rid of the HS, but that doesn't seems to be an option either.
So I'm back to using a triac, finding an available part, that I can heatsink well (I have less than an inch in height, so this will be something custom), and going this route. ST has an
eval board that doesn't do what I need, it's closer to 10A, but it's ballpark.
I guess I'm on here wondering if anyone has any advice for this type of application, maybe something I missed?