Author Topic: PSU supporting both 120v and 240v.  (Read 8276 times)

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Online wraper

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Re: PSU supporting both 120v and 240v.
« Reply #25 on: June 11, 2019, 05:34:26 pm »
My TV, computer monitors and laptop PSUs do not have active PFC either.
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?
 

Offline CJay

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Re: PSU supporting both 120v and 240v.
« Reply #26 on: June 11, 2019, 05:35:51 pm »
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I suppose you could design a PSU that detected input voltage and switched but I do not think they are common at all.


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.
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.

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

« Last Edit: June 11, 2019, 06:02:57 pm by CJay »
 

Offline David Hess

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Re: PSU supporting both 120v and 240v.
« Reply #27 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.
 

Online wraper

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Re: PSU supporting both 120v and 240v.
« Reply #28 on: June 11, 2019, 05:48:09 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.
3. Just design so it works in wide voltage range. Quite easy with say flyback or forward converter topology.
 
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Offline Nerull

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Re: PSU supporting both 120v and 240v.
« Reply #29 on: June 11, 2019, 06:04:34 pm »
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.
 

Offline David Hess

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Re: PSU supporting both 120v and 240v.
« Reply #30 on: June 11, 2019, 06:28:27 pm »
3. Just design so it works in wide voltage range. Quite easy with say flyback or forward converter topology.

That comes at a cost and performance disadvantage compared to doubling or not doubling the voltage at an earlier stage.  Some low power converters work that way though and of course universal input power factor correction stages do exactly what you suggest at high powers but they are not dealing with high transformation ratios.
 

Online wraper

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Re: PSU supporting both 120v and 240v.
« Reply #31 on: June 11, 2019, 06:32:21 pm »
3. Just design so it works in wide voltage range. Quite easy with say flyback or forward converter topology.

That comes at a cost and performance disadvantage compared to doubling or not doubling the voltage at an earlier stage.  Some low power converters work that way though and of course universal input power factor correction stages do exactly what you suggest at high powers but they are not dealing with high transformation ratios.
Virtually all prone chargers work this way.
 

Offline David Hess

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Re: PSU supporting both 120v and 240v.
« Reply #32 on: June 11, 2019, 06:41:50 pm »
3. Just design so it works in wide voltage range. Quite easy with say flyback or forward converter topology.

That comes at a cost and performance disadvantage compared to doubling or not doubling the voltage at an earlier stage.  Some low power converters work that way though and of course universal input power factor correction stages do exactly what you suggest at high powers but they are not dealing with high transformation ratios.

Virtually all prone chargers work this way.

Phone chargers are low power.
 

Offline soldar

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Re: PSU supporting both 120v and 240v.
« Reply #33 on: June 11, 2019, 06:51:56 pm »
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?
You are not responding to my questions. You are changing the subject.  Again: Where is the regulation that says appliances over 75W need to have active PFC? Where? Because I am not saying it does not exist. I am saying the regulation that I have already cited twice does not require it. And between IEC_61000-3-2 and your vague and unsupported assertions I am afraid I have to go with the former.

And, yes, I have opened my Dell 90W power brick as I discussed recently in another thread. You can find it easily.

Again, look, it seems you just want to argue for the sake of arguing. I am not saying I am right. I am just showing the evidence that I have but you contradict it without any evidence whatsoever. Just show me where it says active PFC is mandatory in the EU. I will be glad to see it and learn. Please show us the evidence. What regulation is it?
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 
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Offline David Hess

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Re: PSU supporting both 120v and 240v.
« Reply #34 on: June 11, 2019, 07:09:29 pm »
... Where is the regulation that says appliances over 75W need to have active PFC? Where? Because I am not saying it does not exist. I am saying the regulation that I have already cited twice does not require it. And between IEC_61000-3-2 and your vague and unsupported assertions I am afraid I have to go with the former.

...

Just show me where it says active PFC is mandatory in the EU. I will be glad to see it and learn. Please show us the evidence. What regulation is it?

The regulations do not specifically require PFC but instead specify a maximum input harmonic distortion for different power levels and classes.  Usually the most economical way to meet the specifications is to use active PFC although sometimes passive PFC is sufficient.

https://en.wikipedia.org/wiki/IEC_61000-3-2#Scope

Incidentally, industrial uses may be charged extra based on their power factor but doing this has been considered impractical for consumers so far.  So instead they regulate it on the supply side now.  It was not a big deal until switching power supplies became ubiquitous.
« Last Edit: June 11, 2019, 07:12:16 pm by David Hess »
 

Online wraper

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Re: PSU supporting both 120v and 240v.
« Reply #35 on: June 11, 2019, 07:16:45 pm »
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?
You are not responding to my questions. You are changing the subject.  Again: Where is the regulation that says appliances over 75W need to have active PFC? Where? Because I am not saying it does not exist. I am saying the regulation that I have already cited twice does not require it. And between IEC_61000-3-2 and your vague and unsupported assertions I am afraid I have to go with the former.

And, yes, I have opened my Dell 90W power brick as I discussed recently in another thread. You can find it easily.

Again, look, it seems you just want to argue for the sake of arguing. I am not saying I am right. I am just showing the evidence that I have but you contradict it without any evidence whatsoever. Just show me where it says active PFC is mandatory in the EU. I will be glad to see it and learn. Please show us the evidence. What regulation is it?
I did not mean regulation requires PFC. Well, I was wrong about it being about power factor, it was about harmonics. PFC is a way how to do it relatively cheap and easy, maybe wording was not the best. Also it makes easier to get good performance out of SMPS part.
Quote
You are not responding to my questions. You are changing the subject.
Too much ego on your side. IMO it was already clear what regulation was about. Yet I guess it's not enough attention for you to say about it only twice.
Quote
you are not responding to my questions.
Which questions even vaguely addressed to me?  :-// I did not see a single one. I cannot read your thoughts.
« Last Edit: June 11, 2019, 07:30:51 pm by wraper »
 

Offline soldar

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Re: PSU supporting both 120v and 240v.
« Reply #36 on: June 11, 2019, 07:38:20 pm »
The regulations do not specifically require PFC but instead specify a maximum input harmonic distortion for different power levels and classes.  Usually the most economical way to meet the specifications is to use active PFC although sometimes passive PFC is sufficient.

https://en.wikipedia.org/wiki/IEC_61000-3-2#Scope

Incidentally, industrial uses may be charged extra based on their power factor but doing this has been considered impractical for consumers so far.  So instead they regulate it on the supply side now.  It was not a big deal until switching power supplies became ubiquitous.
Yes, that's pretty much what I said.

I just realized I had not thought about my inverter split air conditioner units which I am pretty certain they would have active PFC.

To get back to the OP subject. Low power units like wall warts can have a wide ranging voltage input because efficiency is not of great concern.

Even laptop PSUs may not have active PFC because of space and weight constraints. My Dell PSU does not even have an inrush limiter and I have blown a few fuses in the UK until I inserted a PTC directly in series in the cable itself.

Cheap PSUs for PCs used to have the voltage doubler switch and now are just for a single voltage and do not have active PFC...

Because if they did the would be:

Higher range PSUs have active PFC which raises the voltage to a set voltage and this is in fact a pre-regulator and therefore admit a higher range of inputs (full-range).

Note also that Triac power controllers for incandescent lighting have some filtering but not what I would consider a lot.
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Offline soldar

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Re: PSU supporting both 120v and 240v.
« Reply #37 on: June 11, 2019, 07:46:32 pm »
Which questions even vaguely addressed to me?  :-// I did not see a single one. I cannot read your thoughts.
Look, I do not enjoy arguing, with you or with anybody else.
Read the thread. For example post 24.
Again, I do not want to argue but you asserted some things and even gave specific numbers.
There is nothing wrong with me asking for a cite supporting that.
I never even said you were wrong. I just asked for confirmation and you ignored y question.
And you say I'm the one with ego?  Sheesh.
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Offline dcbrown73Topic starter

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Re: PSU supporting both 120v and 240v.
« Reply #38 on: June 11, 2019, 07:50:31 pm »
Thanks for the enlightening debate (argument?)  I learned a lot from my simple question!   ;D
Why exactly do people feel I should have read their post before I responded?  As if that was necessary for me to get my point across.
 


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