Electronics > Beginners
PSU supporting both 120v and 240v.
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wraper:

--- Quote from: soldar on June 11, 2019, 03:46:41 pm ---My TV, computer monitors and laptop PSUs do not have active PFC either.

--- End quote ---
About TV, maybe, if it's small or really old. As of Laptop PSU, there is 99% chance it has PFC, unless it's Chinese knockoff. How do you even know that? You cannot take apart laptop PSU in non destructive way as covers are welded together. Did you actually measure current waveform?
CJay:

--- Quote from: wraper on June 11, 2019, 02:17:53 pm ---
--- Quote from: CJay on June 11, 2019, 11:09:33 am ---
--- Quote ---I suppose you could design a PSU that detected input voltage and switched but I do not think they are common at all.
--- End quote ---


Are you joking?

The majority of power supplies in PCs for the past two decades have been wide input range or autoswitching, they are by far the most common type, there are even dedicated ICs for detecting line voltage and autoswitching.

--- End quote ---
They don't do any autoswitching except very rare cases. Manually switchable input voltage is still more common than autoswitching. LOW power SMPS usually just work in wide input voltage range. Those of higher power have PFC (works in wide input voltage range as well) which converts input voltage into around 400VDC and then SMPS works from that.

--- End quote ---

Autoswitch used to be *very* common in some PC PSUs and industrial SMPS, Astec used it extensively for instance.

Autoswitch was great except that it had a bit of a habit of blowing up PSUs if it got confused or the SCR went faulty.

It's not common any more now that wide input range is possible and cheap.

*edit*

I'm quite surprised to see this device is still available, I'm pretty sure it's the one (or a very close relative) that I used to see in a lot of power supplies (because it'd glitched and gone into doubler on a 230V supply with the bang and smoke expected):

https://www.st.com/en/thyristors-scr-and-ac-switches/avs10cb.html

David Hess:
There are two ways that common off-line switching power supplies can support both 120 and 240 volt AC inputs:

1. The older method is to use a voltage doubler configuration on the input rectifier for 120 volts AC and disable the voltage doubler for 240 volts AC.  The result is that the rectified DC voltage is always 340 volts.  Switching is accomplished either manually or automatically.  Note however that this supply does *not* support some voltage range between 120 volts and 240 volts AC.

2. The more common method now is to use boost mode active power factor correction which does not care what the input voltage is as long as it is below 240 volts AC and above some minimum value.  The power factor boost stage produces a constant DC output voltage slightly above 340 volts under all allowed input conditions.  Unlike the voltage doubler method, this will work on any AC voltage between 120 and 240 volts.
wraper:

--- Quote from: David Hess on June 11, 2019, 05:42:03 pm ---There are two ways that common off-line switching power supplies can support both 120 and 240 volt AC inputs:

1. The older method is to use a voltage doubler configuration on the input rectifier for 120 volts AC and disable the voltage doubler for 240 volts AC.  The result is that the rectified DC voltage is always 340 volts.  Switching is accomplished either manually or automatically.  Note however that this supply does *not* support some voltage range between 120 volts and 240 volts AC.

2. The more common method now is to use boost mode active power factor correction which does not care what the input voltage is as long as it is below 240 volts AC and above some minimum value.  The power factor boost stage produces a constant DC output voltage slightly above 340 volts under all allowed input conditions.  Unlike the voltage doubler method, this will work on any AC voltage between 120 and 240 volts.

--- End quote ---
3. Just design so it works in wide voltage range. Quite easy with say flyback or forward converter topology.
Nerull:
You have to go really cheap these days to find a consumer PSU that has either a voltage select switch or passive PFC.

One wonders how many things someone can be wrong about while still acting as an authority on a subject.
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