Electronics > Beginners
Improving small unregulated power supplies
Zero999:
--- Quote from: Gyro on October 15, 2019, 03:22:58 pm ---Surely one of the two main reason for an unregulated brick is quietness (that and reliability). Once you've accepted the lower efficiency, aren't you most likely to want a nice quiet linear regulator?
--- End quote ---
Yes, it does seem daft to do that. You might as well go switched mode for the whole thing.
I haven't had any problems with noise from switched mode power supplies which weren't fixable, with a bit of filtering. I've just completed a project with an audio amplifier running off a switched mode power supply. It's for an intercom system that uses dynamic microphones. Firstly, the low level microphone pre-amplifier part was powered from a linear regulator, powered by the switched mode, which directly powered the power amplifier. The biggest problem was hum, due to leakage across the Y capacitor, which was solved by connecting both power supply rails to the chassis with 10µF capacitors and the squeaky noise was removed with a common mode choke and a big inductor in series with the power supply.
Ian.M:
OTOH if you need multiple rails for an item of testgear you are designing, and want it to be fully floating, high frequency DC-DC converters (for ease of filtering) running off a line frequency transformer wallwart may well be ideal if you need to minimize line frequency leakage current.
soldar:
--- Quote from: Gyro on October 15, 2019, 03:22:58 pm ---Surely one of the two main reason for an unregulated brick is quietness (that and reliability). Once you've accepted the lower efficiency, aren't you most likely to want a nice quiet linear regulator?
--- End quote ---
Yes, I have done that in the past. a single transistor and a zener. The main issue is the headroom needed. But, yes, I have done it and will do it again as needed.
The thing with those switching regulators is (1) they are incredibly cheap, (2) more efficient and (3) very simple.
There is no way I can get SMPS for that price. And, at the risk of repeating myself, the purpose is to use the wall warts I already have.
Zero999:
--- Quote from: Ian.M on October 16, 2019, 10:18:14 am ---OTOH if you need multiple rails for an item of testgear you are designing, and want it to be fully floating, high frequency DC-DC converters (for ease of filtering) running off a line frequency transformer wallwart may well be ideal if you need to minimize line frequency leakage current.
--- End quote ---
But by the time you've done that, the money would have been better spent on a better switched mode power supply, with lower leakage current.
Ian.M:
Availability!
You *TRY* finding a SMPSU that has a grounded inter-winding screen and absolutely no secondary side grounding at a half-way reasonable price. Then see how much extra such a PSU with say three outputs is. e.g. +/-15V for your analog circuits and +5V for your logic.
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