Reply 20 of 27, by PentAmd
chiveicrook wrote on 2022-06-07, 12:06:Output shape is important for modern computer PSUs with active PFC, which require at least good sine approximation with short switchover time in case of power failure. Pure sine wave is naturally the best but not strictly required. Very old UPSes might not provide output that is good enough for active PFC PSUs which, in turn, might result in a wide array of symptoms: restarts during voltage fluctuations, increased load and noise or even catastrophic failure.
In contrast, older equipment with PSUs without PFC could run on really dirty power without trouble and older UPSes were often designed around that.
You are probably not a expert of electrical supplies i can read it.
The power factor circuit (PFC) inside in the PSU is trying to adjust the load (which is current) during the whole the sine period (0.2ms at 50Hz), that the load (current) is always propotional to the voltage. In average you will have the power which is neccessary to supply your PC. This is good for the power grid, because the COS PHI is near 1.0
- What happens if you have non sine-wave (e.g square wave) supply like an "old" ups?
Nothing unusual. The PFC is rectifying the square wave, and it will be an almost constant DC, where not much power-factor-correction necessary. The second stage switch-mode-power-supply is converting down to necessary voltage, and ready.
The switchover between the grid supply and UPS is also not a problem, the PSU has a large enough capacitor in the first stage.
-Why big companies trying to sell Sine-Wave capable UPS devices, if sine wave not necessarly?
Maybe because of backwards compatibility because people are trying to supply all kind of devices via UPS. See end of my previous post.