Originally Posted By: mlord
The buck regulator is a standard circuit from the LM2695S-ADJ datasheet. The datasheet says "45V absolute maximum; but only up to 40V for the operating range".

So we're under 40V, I'd just like a little more margin, or some protection against the odd spike


Well, at some point during our holiday last week, the regulator stopped passing current. Warm (but not hot) to the touch when I inspected it today. Probably had a line surge from an electrical storm last week, and killed the buck regulator.

So I've installed my "spare" module, and the thermostat is working fine again for now.

At some point in the past year, the LM2576HV chip has made it onto commodity regulator boards such as these. This chip ought to be considerably more robust, with a max operating input voltage of 60V compared to 40V for the LM2695S. So I've ordered one (plus a spare) to replace the current module. $5.24 from HK via eBay.