Aluminium heatsink question

[x-pro]

This radiator has a cooling area of 1040 cm2. Under normal conditions, this parameter is quite sufficient if placed correctly and without a fan.
If industrial application is required, then, of course, calculations are needed.

[catalin gramada]

DO-5 zener package has Tj-c of about 125C/50W=2.5C/W, based on ideal heatsink with 0 C/W thermal resistance, and 1N3325 datasheet from American Micro.

DO-5 insulator thermal resistance is circa 0.6 C/W from AN1040.

I'd suggest Tj is kept below 125C, and your ambient may be as much as 50C, indicating a temp rise of 125-50=75C, with a thermal resistance of 2.5+0.6+0.75= 3.85 C/W, so circa 20W.

Imho your main uncertainty is Tj-c, as that can vary with anode or cathode to stud, and it is not specified by the manufacturer (a big red flag).

This scenario is also for one zener per 100mm heatsink, mounted in the 'middle'.

You may want to use your fan airflow margin, however you need to have a good handle on your ambient, given that you may have multiple zeners heating up the local air.

20W with a 150V zener is 130mA, which is a lot more than the reference current (circa 85mA), so you may be noticeably over 150V.

Thanks. Actually there is 180V 120mA. The max current for nte5294a is 220mA.