30-07-2015, 08:04 AM
(29-07-2015, 09:38 PM)Mark Hennessy Wrote: I'd go along with that...
The LM388T is a good voltage regulator - I have used them - but there are a lot of challenges. The main one being thermal design. Get that wrong and the IC might fail with a short between input and output, which means the unregulated input voltage (9V or more) will find its way to the heater. A crowbar circuit to protect against this would be quite complex.
Variac+mains TX is a lot safer.
Regarding the cheap DVM modules from eBay and other places, I brought a few a couple of years back, and it's fair to say that they exceeded my expectations. They're not as good as the £20+ Lascar types, but it's hard to complain for the price. The only real concerns I had related to the safety of one designed to run straight from the mains, but that's easily avoided in a project like this.
Power supply choice aside, would this be ok for over voltage crowbar protection:
http://www.ti.com/lit/ds/symlink/lm431.pdf
Lawrence.
