Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Power Supplies and Power Supply Design
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 06-21-2019, 05:54 AM   #1
Hitto
Member
 
Hitto's Avatar
 
Join Date: Apr 2019
City & State: Italy
My Country: Italy
I'm a: Knowledge Seeker
Posts: 78
Default Bypassing Passive PFC In ATX Power Supplies

I'm planning to remove and bypass the passive PFC transformer/coil on an ATX power supply.

I don't care about reduced efficiency. I'm worried, howewer, about any problem in terms of increased ripple in the primary rail.

Does the removal of the passive PFC has negligible downsides in terms of increased ripple?

Thank you.
Hitto is offline   Reply With Quote
Old 06-21-2019, 11:15 AM   #2
stj
Great Sage 齊天大聖
 
stj's Avatar
 
Join Date: Dec 2009
City & State: Europe
My Country: some shithole run by Israeli agents
I'm a: Professional Tech
Posts: 22,891
Default Re: Bypassing Passive PFC In ATX Power Supplies

i doubt it effects the ripple.
stj is offline   Reply With Quote
Old 06-21-2019, 03:08 PM   #3
Hitto
Member
 
Hitto's Avatar
 
Join Date: Apr 2019
City & State: Italy
My Country: Italy
I'm a: Knowledge Seeker
Posts: 78
Default Re: Bypassing Passive PFC In ATX Power Supplies

But it reduces harmonics, correct? It looks that it may have some benefits in terms of less stress placed to the components placed onto the primary (based onto the following topic: https://www.badcaps.net/forum/showthread.php?t=67663).
Hitto is offline   Reply With Quote
Old 06-21-2019, 03:31 PM   #4
Stefan Payne
Badcaps Veteran
 
Join Date: Dec 2009
City & State: Northern Germany
My Country: Germany
Line Voltage: 230VAC/50Hz or 400VAC/3P/50Hz
I'm a: Knowledge Seeker
Posts: 1,259
Default Re: Bypassing Passive PFC In ATX Power Supplies

passive PFC is just a big fat coil.
So its only a bridge you need.
Stefan Payne is offline   Reply With Quote
Old 06-23-2019, 09:33 AM   #5
Hitto
Member
 
Hitto's Avatar
 
Join Date: Apr 2019
City & State: Italy
My Country: Italy
I'm a: Knowledge Seeker
Posts: 78
Default Re: Bypassing Passive PFC In ATX Power Supplies

That's good to hear.

If you have more informations about any possible drawback (I'm going to upgrade the primary capacitors from 560uF to 820uF and the goal is to combine as many improvements as possible) feel free to write them.
Hitto is offline   Reply With Quote
Old 06-23-2019, 11:58 AM   #6
Dan81
SNES-powered
 
Dan81's Avatar
 
Join Date: Oct 2013
City & State: Romania
My Country: Bacau
Line Voltage: 230VAC 50Hz
I'm a: Hobbyist Tech
Posts: 1,152
Default Re: Bypassing Passive PFC In ATX Power Supplies

You MIGHT experience slight bulging on some PSUs. YMMV depending on how good was the PSU built.

The one I fixed in that thread you mentioned managed to somehow make a Hitachi HP3 cap (820uF 200v if my memory serves me right) slightly bulge. The PSU is still running fine, although I sold the PC I installed the PSU in and bought a GTX750Ti.
__________________
Main rig:
Gigabyte B75M-D3H
Core i5-3470 3.60GHz
Gigabyte Geforce GTX650 1GB GDDR5
16GB DDR3-1600
Samsung SH-224AB DVD-RW
FSP Bluestorm II 500W (recapped)
120GB ADATA + 2x Seagate Barracuda ES.2 ST31000340NS 1TB
Delux MG760 case
Dan81 is offline   Reply With Quote
Old 07-06-2019, 08:29 PM   #7
momaka
Badcaps Veteran
 
momaka's Avatar
 
Join Date: May 2008
City & State: VA (NoVA)
My Country: U.S.A.
Line Voltage: 120 VAC, 60 Hz
I'm a: Hobbyist Tech
Posts: 9,475
Default Re: Bypassing Passive PFC In ATX Power Supplies

Quote:
Originally Posted by Hitto View Post
But it reduces harmonics, correct? It looks that it may have some benefits in terms of less stress placed to the components placed onto the primary (based onto the following topic: https://www.badcaps.net/forum/showthread.php?t=67663).
No, that would be APFC which puts more stress on the primary caps.

PPFC (large line-connected inductor) *shouldn't* put more stress on any of the primary components. However, the reasons I say *shouldn't* is because there are cases where PPFC can stress the primary caps. Like all inductors, a PPFC coil may produce significant inductive kickback in the event of sudden power loss. Thus, if you live in an area where you get frequent power outages and power dips (or very dirty power), then it may be possible for the PPFC coil to put more stress on the primary caps. But in general, that is very rare. So I suggest you leave it, as you get added benefits of extra filtering from noise on the line input and better PF.

Last edited by momaka; 07-06-2019 at 08:33 PM..
momaka is offline   Reply With Quote
Old 07-11-2019, 06:35 AM   #8
Hitto
Member
 
Hitto's Avatar
 
Join Date: Apr 2019
City & State: Italy
My Country: Italy
I'm a: Knowledge Seeker
Posts: 78
Default Re: Bypassing Passive PFC In ATX Power Supplies

Quote:
So I suggest you leave it, as you get added benefits of extra filtering from noise on the line input and better PF.
It should also limit inrush current, isn't it?

By the way, this power supply has no NTC. Which should be a practice for increased efficiency but I do not like that.

I am planning to add a 2.5 Ohm NTC: I know that the value is usually higher (8-10 Ohm) but it is just for reducing a bit the inrush current.

The rating of the NTC is 5.5A but I do not know if it refers to the instantaneous current or the operating current.

Last edited by Hitto; 07-11-2019 at 06:39 AM..
Hitto is offline   Reply With Quote
Old 07-11-2019, 02:14 PM   #9
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 38,024
Default Re: Bypassing Passive PFC In ATX Power Supplies

NTC has nothing to do with efficiency, once the NTC gets hot the resistance will go down but will not be 0 Ohms so you will have power loss on the NTC.
The purpose of BTC is to limit the inrush current when power is first applied to the circuit, once that is over the NTC should be bypassed so it is no longer in the circuit.
__________________
Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
budm is online now   Reply With Quote
Old 08-02-2019, 03:10 PM   #10
Hitto
Member
 
Hitto's Avatar
 
Join Date: Apr 2019
City & State: Italy
My Country: Italy
I'm a: Knowledge Seeker
Posts: 78
Default Re: Bypassing Passive PFC In ATX Power Supplies

Passive PFC removed. Just noticed there is a 1uF/250V Mylar between "A" and "B" pins where the PFC was desoldered. And a 22uF/50V capacitor with its negative leg connected to "A". Shall I remove just the Mylar?
Hitto is offline   Reply With Quote
Old 08-02-2019, 03:50 PM   #11
Hitto
Member
 
Hitto's Avatar
 
Join Date: Apr 2019
City & State: Italy
My Country: Italy
I'm a: Knowledge Seeker
Posts: 78
Default Re: Bypassing Passive PFC In ATX Power Supplies

More informations.

This is a F.S.P. with almost the same design:
https://www.anandtech.com/Gallery/Album/312#3

No mylar but the 22uF capacitor is there.
Hitto is offline   Reply With Quote
Old 08-04-2019, 08:03 AM   #12
Hitto
Member
 
Hitto's Avatar
 
Join Date: Apr 2019
City & State: Italy
My Country: Italy
I'm a: Knowledge Seeker
Posts: 78
Default Re: Bypassing Passive PFC In ATX Power Supplies

I've found several revision based onto the same design and looked at the differences.

This one is without PFC:

(From: www.hardwaresecrets.com)

The differences:
1) Anti-series diodes
2) 22uF/50V capacitor
3) 1uF/250V Mylar capacitor

Simply bypassing the PFC will at least short the 1uF/250V capacitor, connecting both its legs together as it had, prior to PFC bypassing, one leg connected on the input wire of the PFC and the other one connected on the output wire. A snubber, maybe?

The anti-series diode protects the PFC in case of surges and is also suggested on official PDFs of PFC designs. Dunno about the 22uF/50V capacitors and I would like to know its purpose, if possible, for the sake of learning.


Some informations which will be useful to other members of the forum:
This power supply is quite sturdy and worked good as it was, so I was worried about removing the PFC transformer and do more harm than good.

The PFC was measured and, at least in this case, also acts a huge inductor (rated 26mH with a resistance of 0.20 Ohms) making to my opinion things a bit better for at least the diode bridge and the primary caps.

Not simply a matter of bridging two poles because there are also quite a bunch of components around it. I suggest keeping the PFC and the other components. At least in this design.

Last edited by Hitto; 08-04-2019 at 08:40 AM..
Hitto is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2020
Powered by vBulletin ®
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 05:51 PM.
Did you find this forum helpful?