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Cooling an SMA

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Hi all,
I'm currently designing a zener regulator using (0BZG05C8V2 http://www.farnell.com/datasheets/69919.pdf) and i'm hoping to dissipate around 3 watt. Does any one know of a practical way to cool down an SMA (DO-214AC)?

If you check your datasheet, you will see that 3W dissipation is an absolute maximum for this diode. Plus, with a junction-lead thermal resistance of 30 K/W you will have a hard time finding practical way to cool it. Why don't you try and find a part in a larger package?

Put it on the base of an NPN transistor and use it as a shunt?


The only way you'd get anywhere near 3W without it unsoldering itself would be on an aluminium clad board, or with a lot of forced air. If you really need to dissipate that much, spread it over several series devices, or use a heatsinkable package.

Funny how they specify a junction-ambient thermal resistance of < 30 K/W for dissipating 3W, but the thermal resistance between junction and lead is already 30 K/W, so you wouldn't be able to meet the spec even if you soldered it to a huge heat sink. Guess they use forced air to achieve that.

I agree with the others: use some other device (eg. transistor, or regulator) to dissipate the power, or get a zener in a package with a lower thermal resistance.


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