People have been connecting transformers to bridges to caps for ages, and it generally works.
An AC wall-wart will have a lot of internal impedance anyhow. No line spike is going to charge thousands of microfarads very much.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
My objective is to get switching supplies as far away as possible.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Thanks, but I don't want to run the AC line into my box. Hence the preference for an external wart. The AC output warts usually have a single isolated secondary.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Companies are making post switcher LDOs now with very low noise. For example:
They are nice for ultra low noise synthesizers.
Yes, you're right, and primary resistance will be high so surge currents will be limited
Cheers
Klaus
As far as necessary, sure. As far as possible, it's NOT the big problem. Magnetic fields around a leaky line-frequency transformer fall off as 1/ R**3 and distance is cheaper than effective (mu-metal?) shielding.
One foot of distance gives three orders of magnitude improvement over one inch.
But around a 200 kHz switcher, you don't need mu-metal, the skin depth in aluminum is 183 um, so the same three orders of magnitude costs you 1.2 millimeters of aluminum.
Meanwhile, any OTHER item near your sensitive box, that develops a 60Hz field, ruins the pristine voltage source. I've seen a month go by while a high-intensity light's transformer was the dominant problem. A linear regulator is pretty good at rejecting 60 Hz, but it CAN'T do anything about pickup in the output side wires.
How are you going to make a single part automatically switch 115/220?
The pic that I posted at the start of the thread is the classic
120/240 thing. I could always furnish the 240 volt transformer wart and automatically switch. But then I'll have to make a very quiet charge pump to get some negative voltage.Or we could just stock 120 and 240 volt warts and ship the appropriate one. Then the negative could be done at 50/60 Hz, like in the netlist I posted.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
...by sticking a warning label on the widget?
RL
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.