They do exist - I've seen various appnotes. Although a lot of equipment manufacturers still use discrete component designs.Why do you think such chips exist?
It sounds more like a transformer followed by a DC-DC converter, since:
220 VACrms * 1.414 ≈ 311 VACpk
You would need to boost 311 VDC up to 400 VDC
I don't think a power factor chip is going to do that for you. What do you think?
The PFC front end is basically a flyback boost converter, but it has no mains in reservoir electrolytic so it draws pulses of current from the mains that are more or less proportional to the sinewave amplitude - instead of just current blips on the peaks.You still haven't answered the question of how this intermediate voltage comes about. You can't get something from nothing. So show me.
Why do you think such chips exist?
Wow, claiming something does not exist yet claiming it's invention in the same post.If you go back to post #2 you will see that I inferred the existence of a boost converter oits one type.
I made no such claim. Based on the additional information provided, I simply posited that a DC-DC converter must be involved. A DC-DC converter is always more than just a chip as there are several other components involved. What I claim does not not exist is a single chip that does the entire PFC job. I still think that is a reasonable claim.Wow, claiming something does not exist yet claiming it's invention in the same post.
The devices I have seen take a FW single phase input and step up the normally 160 DC to around 370 VDC to feed a bridge inverter. The current in the boost inductor is kept in sync with the input voltage to manage and maintain the power factor.
There are many ways to implement power factor correction, but the most common in medium-to-high power switching power supplies is active PFC based on a boost converter
Ian - a large inductor does attenuate the harmonic content of the input current waveform, but id doesn't automatically bring the power factor to near unity. Many of the PFC regs are written in terms of harmonic content for this reason, because reducing the peak current (a function of a non-sinusoidal current waveform) is more important than the actual phase angel.
So can I do 5kW PFCThere are many ways to implement power factor correction, but the most common in medium-to-high power switching power supplies is active PFC based on a boost converter with two independent control loops. The idea came out of Cal Tech in 1980, and the current form came from someone at Zytec a few years later. They went to Unitrode to grow a custom controller chip to implement the idea, and after a while Unitrode was allowed to sell it to everyone. This was the first PFC controller. Unitrode (now TI) has lotsa app notes explaining how these critters work, inductor design, etc.
After the input bridge rectifier there is no big capacitor. Raw full-wave rectified AC goes to the series inductor of a boost convertor. The shunt FET switch is controlled by two inputs. One tracks the instantaneous input voltage and input current, and pulse-width modulates the FET so the input current waveform matches the input voltage shape and phase. The output of the boost converter goes to a large capacitor, and the second control loop looks at the voltage on the cap, calculates the average power of the circuit with an analog multiplier, and modulates the PWM to increase the average input current and keep the cap topped off. There is a design tradeoff with the size of the boost inductor versus the output ripple voltage. With around 400V on the cap, 50V of ripple is not uncommon. This nominal DC voltage is the power source for downstream isolated DC/DC converter stages, DC/AC inverter stages, or whatever creates the outputs.
I've seen the boost circuit running anywhere from 50 KHz to 500 KHz. Mine ran around 150 KHz. Usually it is in the 100-200 KHz range, and sometimes it is synchronized to the frequency of the downstream stages. This calls for high voltage, high current, high speed rectifiers in both the input bridge and the boost rectifier. The typical active PFC stage is over 90% efficient, and 2nd gen controllers have a 2nd stage that recovers energy from the boost diode and increases overall efficiency to the high 90's.
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