Dummy question about PFC's

[Malmir]

Hey there.

I have seen Donald Duck fatazilions different schematics on SMPS and "traditional" PSU but rarely seen some DIY using PFC's. People claims from time to time that they are demanded, and others that they are nice to have.

Now comes number one silly question on this planet . For what good is a PFC and what estimation should done to choose if or not to use a PFC. Additional question, i might have missed one important point but in many cases it looks like that the supply is shorted to gnd via the FET ? And how come some have lover input voltage than output ?

And before You guess . No i have NEVER used a PFC, nor have i never heard about then at education places.


Sincerely
Klavs.

 

[wally7856]

In general terms without a pfc your smps will draw 30% more current because of the mangled input waveform of a non pfc smps.

 

[Malmir]

Thanks.
This was the short form , does any have a link to or a bit deeper info ? i do wanna try to do a PSU, but unsure about using a PFC or not.
On this site in some the many threads, there is a 6kW schematic, witch have been verifyed on some other sites to, if one should that amp in 2 chanels it would be a huge power supply, even as SMPS. But would the PFC be needed or nice to have here ?

 

[wally7856]

WOW, that is big. PFC would very helpful for that power range, but maybe get the power supply working first and then add PFC to it.

There are many Google hits for PFC and most semi mfgr's have ap notes for them.

 

[Malmir]

Hey Wally.
Semi comps and ap notes, i have seen some, but are more confused, as many delivers a large voltage than input, why is that and is that unavoidable or just easier to do ?

But the way i got stucked in another project as Mr Microsim explained, don't do a SMPS at large size without a good scope and/or even a one with diff input, mine is a rather old Phillips one, thus i do need to wait for some thing cheap comming up . And actually i'm doing an attempt to do my own 4 channel diff input scope to be used for this.

6kW is big 2 to times is bigger yes . But i hawe seen people from ICE Power doing some huge stuff at almost no room, so i am happy to try .

BRGDs
Klavs.

 

[wally7856]

Hey Wally.
“Semi comps and ap notes, i have seen some, but are more confused, as many delivers a large voltage than input, why is that and is that unavoidable or just easier to do ?”

Many PFC’s use a boost inductor / circuit. For a boost circuit to work it must output more voltage than the input. Buck can also be used but these are usually used for low voltage supplies.

“But the way i got stucked in another project as Mr Microsim explained, don't do a SMPS at large size without a good scope and/or even a one with diff input, mine is a rather old Phillips one, thus i do need to wait for some thing cheap comming up :. And actually i'm doing an attempt to do my own 4 channel diff input scope to be used for this.”

I saw this scope on Ebay a few days ago. It will be better than a homemade scope.

Digital 70MHz Oscilloscope 2Channels 1GS/s 7'' TFT LCD 800x480 USB DSO5072P
Price:
US $215.00

ModelSO202
- Sampling rate: 48MHz
- Channel quantity: 2
- Storage depth: 1m
- Voltage resolution: 1V/256
- USB 2.0 high speed data connecting
- Signal measurement input: Min. -50V, Max. +50V (probe x 10)
- Max. Measurement frequency: sine wave (-15MHz), square wave (-5MHz)
- Data storage format: OSC / CSV
- Sampling rate range: 0.125MHz~8MHz



“6kW is big 2 to times is bigger yes :. But i hawe seen people from ICE Power doing some huge stuff at almost no room, so i am happy to try :.”

You will spend a lot of money blowing up components. Start with a very small SMPS where components are inexpensive.

 

[Malmir]

>>You will spend a lot of money blowing up components. Start with a very small SMPS where components are inexpensive.
Oh that i will and do, actually by "cheating" with a 50V in front of to start with (and recalculated feedbacks and so on).

 

[Malmir]

Wally: That scope is digital for sure, but it looks like a standard scope, or am i wrong ?, i thought of an differential input scope.

 

[wally7856]

I think only the best professional scopes have differential inputs $$$.

 

[smps_fan]

Is it the cheapest way to just buy a differential probe ?

 

[Malmir]

:-( looked a prices, and sure if one should have a differential scope, he needs to rub a bank first :-(.

 

[smps_fan]

Yes, I think it´s better to buy a cheaper scope and then just a differential probe ! There are payable ones which also cost much but payable.