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Old Dec 28, 2009, 03:26 AM
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PLD
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Australia, QLD, Charters Towers
Joined Dec 2003
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Finally got some thermal testing done of the BAC unit and it's not quite as good as I want at the moment.

With an ambient of 29'C, no airflow, drawing 2.2A @ 5.35V into a 2.5R dummy load, the heatsink gets up to 85'C and the regulator goes into "thermal shutdown" mode after a 2 minutes. At this level the heatsink is trying to dump off about 5.8W of heat.

If positioned in the airflow the setup would tolerate a higher constant current.

If I raise the voltage up to 5.5V then the heat dissipated will be a bit less but not significantly so ( P = IV, so P1 = 2.2 x 2.65 = 5.8W, vs P2 = 2.2 x 2.5V = 5.5W )

Not that there's anything profoundly unusual here to be honest, rarely can you do the rated current on regulators constantly without quite large heatsinks.

The realistic thing to do here is write up the specifications much like I have with the smaller BACs,

Constant rating (eg 1.5A), 1 minute rating (eg, 2A) and 10~30 second rating (eg 3A).

Paul.
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