Make an pfc buck type with an dc-dc buck ic controler

Thread Starter

Danilo1988

Joined Dec 14, 2020
13
Hi my very good friends from AAC if possible i want to know if some one have every did an pfc with an simple buck ic controller not those complicated IC PFC controller but instead with an simple buck controller i have in mind an LM2576 i found to be very limited options to buck type pfc controller and all then with so much complication and obviously overengineered.

some one can say me if had to much drawback in do it so for low consumption devices like 100watts im think in use this component lm 2576 and use an mosfet driver with signal inversor because is an open drain.

some one more advance can say if have some drawback not using an truth controller to that task ?


 

Papabravo

Joined Feb 24, 2006
15,732
Hi my very good friends from AAC if possible i want to know if some one have every did an pfc with an simple buck ic controller not those complicated IC PFC controller but instead with an simple buck controller i have in mind an LM2576 i found to be very limited options to buck type pfc controller and all then with so much complication and obviously overengineered.

some one can say me if had to much drawback in do it so for low consumption devices like 100watts im think in use this component lm 2576 and use an mosfet driver with signal inversor because is an open drain.

some one more advance can say if have some drawback not using an truth controller to that task ?


It seems like a stretch. Is there some reason to feel that this is possible?
The purpose of PFC is to change the relationship between the current and voltage waveforms in an AC signal. The purpose of a buck converter is to chop a higher voltage DC waveform into a lower voltage waveform with a DC component that is smaller than the origina DC input and has a "small" AC component as a result of the action of the switch. I think I can state categorically that these two concepts appear to be unrelated.

If wishes were horses then beggars could ride.
 

schmitt trigger

Joined Jul 12, 2010
422
By the time you would spend making a circuit kludge which would still work inefficiently, you could have learned PFC theory several times over.

You are correct that some very high performance devices are quite complex.

But if you can live with a little lower efficiency and performance, there are several ICs which are surprisingly simple to work.

ST Micro has the L6561, in a 8 pin package which is fairly easy to understand.
 

Thread Starter

Danilo1988

Joined Dec 14, 2020
13
It seems like a stretch. Is there some reason to feel that this is possible?
The purpose of PFC is to change the relationship between the current and voltage waveforms in an AC signal. The purpose of a buck converter is to chop a higher voltage DC waveform into a lower voltage waveform with a DC component that is smaller than the original DC input and has a "small" AC component as a result of the action of the switch. I think I can state categorically that these two concepts appear to be unrelated.

If wishes were horses then beggars could ride.
 Hi Friend in my understand an buck topology PFC controller have very similar function to an buck DC-DC controller both can make an higher voltage become an lower voltage. that to my understand is the main function of an buck type pfc controller.

The main problem of an non active PFC design is that we have an very high current in an very limited amount of time (in the senoid) right ? the buck DC-DC controller would eliminate that isnt ? because it would transform the high voltage (pulsing DC) to an voltage to charge the capacitor bank that in short would make the current be more linear through the conduction angle (before the ac wave get lower than the desired output ) that is essential the same thing an Buck pfc controller would do.
 

Thread Starter

Danilo1988

Joined Dec 14, 2020
13
By the time you would spend making a circuit kludge which would still work inefficiently, you could have learned PFC theory several times over.

You are correct that some very high performance devices are quite complex.

But if you can live with a little lower efficiency and performance, there are several ICs which are surprisingly simple to work.

ST Micro has the L6561, in a 8 pin package which is fairly easy to understand.
Hi my Friend that topology seems to be an boost type topology you understand smps ? i need some one to help me designed an non isolated circuit and im looking for some one that can help me with some problem that im facing, i have several simple to design boost topology but since is an non isolated topology i would prefer an buck type (need to be very small, boost type capacitor are far larger as well the inductors )

with an non-isolated circuit the only requirement is an very good isolated device right ? my doubt is if an 1mm abs plastic would make it safety i know that in general 2.53mm air gap is enough to protect danger spikes from the grid but plastic dont need to be 2.53mm thick need ? if some one could help me with that i would appreciate a lot and if you or some one want to help me make this design we can negotiate an monetary reward

thanks in advance
 

Papabravo

Joined Feb 24, 2006
15,732
 Hi Friend in my understand an buck topology PFC controller have very similar function to an buck DC-DC controller both can make an higher voltage become an lower voltage. that to my understand is the main function of an buck type pfc controller.

The main problem of an non active PFC design is that we have an very high current in an very limited amount of time (in the senoid) right ? the buck DC-DC controller would eliminate that isnt ? because it would transform the high voltage (pulsing DC) to an voltage to charge the capacitor bank that in short would make the current be more linear through the conduction angle (before the ac wave get lower than the desired output ) that is essential the same thing an Buck pfc controller would do.
Can uou give me a link to something that puports to do what you want to do?
How exactly does lowering the AC voltage bring the voltage and current waveforms closer together in phase?
BTW I thought the L6561 was a solenoid driver. Maybe I'd better pull a datasheet.

I see the problem. I was thinking it was an AC-AC device where you are trying to correct for power factor less than 1. What the L6561 is doing is converting AC to DC at line voltage. Explain to me what is the power factor of the incoming AC and what are you trying to correct for?
 
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Thread Starter

Danilo1988

Joined Dec 14, 2020
13
Can uou give me a link to something that puports to do what you want to do?
How exactly does lowering the AC voltage bring the voltage and current waveforms closer together in phase?
BTW I thought the L6561 was a solenoid driver. Maybe I'd better pull a datasheet.

I see the problem. I was thinking it was an AC-AC device where you are trying to correct for power factor less than 1. What the L6561 is doing is converting AC to DC at line voltage. Explain to me what is the power factor of the incoming AC and what are you trying to correct for?
Hi buddy i think you are made an mistake diferent from AC shifting in phase (current vs voltage ) in an SMPS the only difference that make pf low is that we have an very short period where the capacitor charges itself (when the voltage aloud to the current to flow ) an buck topology would make that be more linear by lowering the voltage an making the system draw current in an more wide angle of the sinusoid


image hosting
 

Papabravo

Joined Feb 24, 2006
15,732
Hi buddy i think you are made an mistake diferent from AC shifting in phase (current vs voltage ) in an SMPS the only difference that make pf low is that we have an very short period where the capacitor charges itself (when the voltage aloud to the current to flow ) an buck topology would make that be more linear by lowering the voltage an making the system draw current in an more wide angle of the sinusoid


image hosting
Thank you for the graphical illustration. I was not aware that this situation existed much less that it required correction. With sinusoidal waveforms for current and voltage the pf is the cosine of the phase angle between the current and voltage waveforms. What does the calculation of power factor look like for the red and blue waveforms?
 

Thread Starter

Danilo1988

Joined Dec 14, 2020
13
Thank you for the graphical illustration. I was not aware that this situation existed much less that it required correction. With sinusoidal waveforms for current and voltage the pf is the cosine of the phase angle between the current and voltage waveforms. What does the calculation of power factor look like for the red and blue waveforms?
Sorry buddy i dont know if you are being sarcastic or not but in short i dont know the calculation exactly but when the current curve is more close to the sinusoidal curve we have an better PF with out any current control the current wave is mess up
 

Papabravo

Joined Feb 24, 2006
15,732
Sorry buddy i dont know if you are being sarcastic or not but in short i dont know the calculation exactly but when the current curve is more close to the sinusoidal curve we have an better PF with out any current control the current wave is mess up
No sarcasm. This is in the realm of "new physics" for me and I am genuinely interested in the method of establishing the actual power factor without correction for the purpose of determining how close we can get to ideality for the waveform on the right.

EDIT: I see the problem. The term "power factor" is properly applied ONLY to sinusoidal waveforms with the same frequency. What can be done with the non sinusoidal waveform is to decompose it into a sum of sine waves. Only the component at the same frequency as the voltage waveform will contribute to the power factor. That is why it was "new physics" - it doesn't really apply to this case. I don't know why this characterization has gained currency, but who am I to argue.
 
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