Hi. There is speculation that the 240v ac mains over here in britain contains some dc and that dc can upset the transformer in a linear power supply. With an smps the 240v ac mains is rectified then filtered to produce 240v dc. If there is a dc component in the mains it should not matter to an smps and the noises, hum etc associated with a linear power supply should disappear. Shouldn't it?
Easy to measure the DC component of mains with a multimeter if its rated for high voltage DC measurement. Locally I see 243Vac with 0..10mV of DC offset. That doesn't surprise me, the local distribution substation transformer doesn't let DC through.
SMPS generate much more noise than a linear supply, although much of it may be above the audio band. Instead of large filter caps you can add noise filtering.
SMPS generate much more noise than a linear supply, although much of it may be above the audio band. Instead of large filter caps you can add noise filtering.
You can feed those things pure 340V DC and they will be utterly happy.
The front-end works same-as old US "AC/DC" radios. Rectifier, capacitor. When plugged to DC (we used to have DC power in small areas, though that's not why "AC/DC" radios existed) the rectifier does no good, but no harm either.
Once we get to raw DC, SMPSs turn that DC to 50KHz AC; this process does not care how the DC was made.
The front-end works same-as old US "AC/DC" radios. Rectifier, capacitor. When plugged to DC (we used to have DC power in small areas, though that's not why "AC/DC" radios existed) the rectifier does no good, but no harm either.
Once we get to raw DC, SMPSs turn that DC to 50KHz AC; this process does not care how the DC was made.
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The 240 volt input ones work fine. The 120 volt input supplies with the voltage doubler rectifier won’t. However, most of those actually have a full wave rectifier, with half of it bypassed - and moving one jumper wire convers it to 240V input.
Some PFC supplies may work ok with DC input, others may not. The PFC feature can usually be defeated, if need be.
Some PFC supplies may work ok with DC input, others may not. The PFC feature can usually be defeated, if need be.
Thanks!
Was there ever really a problem with dc in the mains concerning linear psu's or was this made by the manufacturers. Read all kinds of posts about people putting huge capacitors in their mains to block dc.
Sorry, totally off topic, is there any problem with using safety mains x1 x2 caps in speaker crossovers. I am wanting to buy some caps and the polypropylene x1 x2 are looking so cheap. Can they be compared with the fancy ones.
Thanks
Was there ever really a problem with dc in the mains concerning linear psu's or was this made by the manufacturers. Read all kinds of posts about people putting huge capacitors in their mains to block dc.
Sorry, totally off topic, is there any problem with using safety mains x1 x2 caps in speaker crossovers. I am wanting to buy some caps and the polypropylene x1 x2 are looking so cheap. Can they be compared with the fancy ones.
Thanks
As written above, the (unauthorized) non-symmetrical loading causing a DC-component has to be on the same side of the local transformer station as you and has to pull considerable power. A rare situation.
I have lived in more EU-continental countries and never experienced the problem.
NB: "Hum" may come from the safety capacitor connected between the primary and secondary of an SMPS for EMI reasons. I have had situations where an SMPS caused hum while a traditional transformer supply did not. Hum is tricky.
50/60Hz transformers (particularly toroid) "can" be flux-unbalanced by DC on the power line.
IMHO DC on utility lines is fairly unlikely, and if present, small. Where does your AC come from? A *transformer* within sight of your house. The utility transformer has low-low DC resistance (if it was large, the AC would sag but also the utility transformer would heat and have shorter life).
Agreed. The tight magnetic circuit of toroid cores is easily driven toward saturation by D.C. current. I live in a relatively rural area, seemingly, far removed from industrial scale reactive loads, and yet, occassionally experience humming from the toroidal transformer of my power amp. Not often enough to force me to implement a fix, but it does happen on rare occasion.
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