12-05-2011, 06:20 PM
My two-pennyworth.....
I used to try to use switched-mode supplies in my amateur radio days. And very nice chunky things they were too. Made by people like Advance. Chunky but very compact and cool running. Ideal for chucking out 20A at 12V without breaking sweat.
But (and there is always a but) switch-mode supplies always radiate a lot of "hash" no matter how well the designers filtered every input and output. A homemade thyristor supply will produce variable voltages, but the switching speed is quite fast, so you get a sharp "edge" to the waveform. As you probably know, anything looking "sharp" on a scope means lots and lots of harmonics. In this case well up to 30MHz and beyond.
So if you have any radios on the bench, or even nearby, your thyristor PSU (which will not have industrial-grade filtering) may well be a rather effective broadband transmitter as well!
I'm afraid I'm a luddite - I like nice linear PSUs that glow red hot but are very electrically quiet.
Two pennyworth now over...
all the best
Jeremy
I used to try to use switched-mode supplies in my amateur radio days. And very nice chunky things they were too. Made by people like Advance. Chunky but very compact and cool running. Ideal for chucking out 20A at 12V without breaking sweat.
But (and there is always a but) switch-mode supplies always radiate a lot of "hash" no matter how well the designers filtered every input and output. A homemade thyristor supply will produce variable voltages, but the switching speed is quite fast, so you get a sharp "edge" to the waveform. As you probably know, anything looking "sharp" on a scope means lots and lots of harmonics. In this case well up to 30MHz and beyond.
So if you have any radios on the bench, or even nearby, your thyristor PSU (which will not have industrial-grade filtering) may well be a rather effective broadband transmitter as well!
I'm afraid I'm a luddite - I like nice linear PSUs that glow red hot but are very electrically quiet.
Two pennyworth now over...
all the best
Jeremy
