I have a couple of homebuilt DC regulated supplies that I built a great many years ago, the first is a simple 3A 13.5V one that was the very first supply I ever built and it used a 723 with a single 2N3055 series pass transistor. I remember I bought a lovely oil filled mains transformer for it, but accidentally wired up the 120V windings in parallel instead of series for our 240V mains and watched it start to bulge when I switched it on. (after I put a bigger fuse in it). I ended up using another transformer and the power supply is still in daily use, built in the early 70's.
I later built a 25 Amp version with 4 3055s and a 723 with overvoltage trip, and also short circuit protection. It can be shorted out and with barely a spark it trips out and has to be reset before it comes on again. No fuses to blow and replace, no destroyed series pass transistors. I built it in a chassis that was lying around and 35 years later it is still in daily use and still not got a proper cover made for the chassis. I checked the output the other day on my scope to see if there was any hum or ripple and on full load I had 10mV p-p of noise. Regulation still excellent. Nothing much wrong with the humble 723. I have seen some truly awful "commercial" supplies with no short circuit protection, that blow the series pass transistors like fuses, or worse make them into short circuits that apply the full unregulated supply on to the load. 73 from David GM4JJJ > On 22 Jul 2016, at 15:55, Alan Bloom <n...@sonic.net> wrote: > > The 723 regulator has some known reliability issues, but with proper design > they can be mitigated. In particular the differential voltage on the error > amplifier inputs is only rated for 5v. If one input is connected to the > 7.15V reference, then if the power supply output is shorted the voltage > rating is exceeded. The solution is a strategically-placed diode. > > Alan N1AL > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
