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Is this this circuit going to revolutionise Switch Mode Power Supplies worldwide?

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Flyback

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Hello,
We are doing a 3kW battery charger (Vin = 230VAC, Vout = 250 – 420VDC)
We wish to use the modified Cuk converter to do this. This converter does not need a mains diode bridge before it, and does not need an isolating SMPS stage downstream of it. The Cuk converter does the whole job by itself and needs no other circuits.
Do you think this is possible? Dr Slobodan Cuk seems to think so (as in link below)
Why is the current in the L1 always discontinuos? Can this circuit not operate in Continuous conduction mode?
Also, the series capacitor, C1, suffers 15 Amps of ripple current, and has to be rated to 600V (and must not be of polar type like an electrolytic), and has to be at least 100uF. Why does this capacitor have to be of such big Faradic value?
The attached is a simulation of our work so far of the Cuk converter. –Also the schematic of our work so far.
Here is the link to the pioneer of this breakthrough power supply circuit, and the details of it….
https://www.power-mag.com/pdf/feature_pdf/1310569074_Teslaco_Feature_Layout_1.pdf
The link is 4 years old, howcome nobody is doing this now?….why bother with a mains diode bridge and a downstream isolating converter if its not needed.?
 

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  • Cuk PFC SCHEMATIC.pdf
    12.2 KB · Views: 177
  • Cuk PFC.asc
    2.9 KB · Views: 138
how come nobody is doing this now?
Difficulty sourcing the required components, perhaps ;). Have you checked the voltages appearing across the switch?
 
The attached LTspice simulation and schematic show an improved version of the special PFC circuit, but the voltage and/or current waveforms are too peaky in this converter…
Also, the transformer is suffering enormous voltage spikes. I believe that this needs a energy recycling snubber to be used with it….so has Dr Cuk not given us enough information to implement his fantastic converter with? Perhaps he is understandably only divulging the basic detail? –not enough to achieve implementation?
The circuit is a resonant circuit, and L3 is the resonant inductor, and C1 is the resonant capacitor. I thought that the LC resonant frequency would need to be roughly at the switching frequency but that gives poor performance….the power throughput cannot be made high enough that way.
If C1 is too low Faradic value then C1 has too high voltage across it. If L3 has too low value then the peak current is too high. If L3 is too high Henry-ic value, then the current throughput goes down and you can’t get the power throughput.
The transformer primary would need a heavy snubber, and this would be very dissipative, unless some kind of energy recycling snubber was implemented. The problem is, where would you recycle the energy too?….since there is no storage capacitor on the primary side, and recycling to the secondary needs another isolation transformer.
The circuit would obviously need a controller to control it…but there is no “primary ground” to use to ground such a controller to. Therefore, an output of an isolated SMPS would need to be used to “ground” the controller to. Then the sensed current and output voltage signals would need to be referred to this isolated ground. The necessary fast current sense in the power FET loop will be difficult, because this will have to be transferred across an isolation barrier to the control chip, and this will be difficult. A hall sensor would have to be used, but they have poor bandwidth which would mess things up.

Does anyone know how to set the component values for this converter? The only advantage of this modified cuk converter appears to be that you can dispense with the mains diode bridge. But in exchange, one needs to have a lot of extra housekeeping circuitry to manage the control of this converter. This seems unwise, since a mains rectifier bridge only cost about 30p, and only dissipate about 1.5% of the total power budget.
 

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  • Cuk PFC _1_schematic.pdf
    13.6 KB · Views: 162
  • Cuk PFC _1.asc
    3.3 KB · Views: 151
1) The switch is bidirectional.
2) The switch needs to withstand 3x the power line voltage. Maybe 4x.
3) The switch needs to carry a peak current way above the average.
equals big money for the switch.
 
Thankyou. It is interesting that Dr Cuk, in the article linked in to the first post, did not mention these downsides. The only downside that Dr Cuk mentions is the need for a special controller, and difficulties interfacing it to the circuit signals.
Also, do you not think that the primary will need a very big snubber, either that or some kind of complex energy recycling circuit.?

By the way, I hope you did not think its higher current in the fet because of my simulation?....because I did not do a proper PFC algorithm, I just did a constant 0.5 duty cycle at all times so my FET current is larger than it would be in a "proper " Cuk PFC system.

By the way, as Dr Cuk says, this circuit is especially useful for you guys in the States, because it means you don't need a front end bridge rectifier, and in US mains, the 110vac rating means there is more loss in the mains rectifier, so doing away with it would be great for the USA. -But good for all, and as such, I am surprised that this Cuk converter PFC is not being used?
 
I only think high current because of discontinuous current.
At the valley of the 50/60hz there will be zero current. At the peak of the power line voltage the current will be high. (1.414x average)
If you look at the output ripple you will see 100/120hz noise. Problem with any PFC that does not down side regulate.
The error amp must be very slow. It can not see any 100hz noise or the PFC will on work.
 
I am surprised that this Cuk converter PFC is not being used?
Well I'm not surprised, given all the disadvantages :).
 
thanks, but some of the disadvantages being put forward are disadvantages that we get with normal boost PFC stages. Do you know what is the real showstopper for Dr Cuk's "single stage, mains_rectifier_less PFC circuit"?
 
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If the Cuk converter is so great, why hasn't it been used more? Invented ~1976 you would think if it is good it would be in more use. Lot's of college thesis available on line about how to implement them. But being a DC-DC converter don't know about them not using an input bridge?
 
See post #4.
If the Cuk converter is so great, why hasn't it been used more? Invented ~1976
There are several "Cuk converters".
I have put one type of Cuk converter into production.
I have tried several.
My biased onion (may not be true):
Cuk works for a university and not for the real world.
He tries very hard to make something novel. He is cleaver. I am not putting him down.
In the above example the "transistor or switch" must withstand a very high voltage, high current (compared to other types) and must switch both positive and negative current. Like many other university projects, this transistor does not exist.

The Cuk converter I did use was good. Did what it should. One capacitor has huge current. As long as the designer knows that, it work well.
 
In the above example the "transistor or switch" must withstand a very high voltage, high current (compared to other types) and must switch both positive and negative current. Like many other university projects, this transistor does not exist.
thanks, by the way, the article suggests that this transistor get done with two back to back nfets. But I agree, the voltage seems very high, the snubber would need to be able to handle the bidirectionality so would be a very clever snubber.
 
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