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very bad very bad very bad Why didn’t they design the frequency regulation for this chip so that it could be used at low loads and at the same time be used at high loads???? Thank you.
I don't understand your question. The UCC28070 is a PFC boost-controller and regulates output voltage, not frequency. The voltage is regulated at low loads as well as high loads. The switching frequency is fixed value that is chosen by the PFC designer.
Hello, you didn’t understand me, when a 4 kW PFC operates at low loads, the SCM mode ends - the controller switches the choke to intermittent mode, which leads to overheating of the magnetic circuit, in order to return the controller with the choke to its original state, SCM mode, you either need to lower the voltage by input of the inductor, or increase the frequency at which the controller and inductor operate, As the frequency increases, the inductor increases its resistance, the current through it decreases and the controller is forced to switch to SCM mode from the intermittent mode, the inductor stops heating, and thus A PFC can work optimally as a voltage stabilizer at high and low loads, that is, it would be nice if the 28070 could also automatically change the frequency depending on the load, Am I right??? Thank you for your attention,
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Hello, you didn’t understand me, the 4 kW KKM works at low loads when the SCM mode ends
You are right, I don't understand what you are trying to tell me. Please define what you mean by SCM mode and intermittent mode. In a web search, could not find a reference to these modes in the context of PFC design.
But maybe you are referring to continuous conduction mode (CCM) and discontinuous conduction mode (DCM) of current in the inductor? In a fixed-frequency boost converter, at some current level (light load), inductor current will change from CCM to DCM. This is not a heating problem. The inductor does not heat up at light loads, it cools down. DCM operation has no effect on the output voltage regulation.
A different type of boost-PFC that has automatic variable frequency operates the inductor current in transition mode (TM) sometimes also known as critical conduction mode (CrCM or CrM) or boundary conduction mode (BCM or BM). Here the inductor current operates the transition point or boundary between CCM and DCM. The switching frequency changes with peak current: lower frequency at higher peaks and higher frequency at lower peaks. Maybe that is what you are thinking of.
TM-PFC is usually not considered practicable to use at power levels higher than 1kW, and is usually used between 100W to ~800W. Theoretically, TM-PFC can be used at any power level, even megawatts, but the "limitation" to <1kW is due to practical considerations of the peak currents through the power-processing components (inductor, switch, diode, etc.)
To conclude, the UCC28070 fixed-frequency CCM-PFC is well suited for use in a 4kW application. Output voltage regulation is maintained from 0% to 100% load, and there is no heating of magnetics at light load. The worst heat (power loss) is at full-load, at the lowest input voltage.
I don't know why you were not able to get permission to download TINA-TI. Maybe you forgot to fill in some necessary information, or one of your entries was not acceptable. Please try again, but I cannot guarantee that it will work.
I also don't know why Webench will not allow user-selection of minimum frequency. Webench is a simplified design program and does not accommodate all possible design decisions, but it seems like minimum frequency should be a selectable design parameter. Please use the Excel tool for designing. Webench can give you an idea of the circuit topology and component configurations.
Hello, your company does not want to share Tinati with me so that I can deal with the ucc28070.... Help me, at least with some answers... will the ucc28070 fully work on one phase if the second is stopped through grounding Cao? ?? what will be the efficiency of a 5kW PFC 28070 at a load of up to 1kW??? Do you happen to have a graph of the threshold for the transition of the PFC from the СCM mode to the relay mode (percentage of load - percentage of input voltage)??? Thank you for your attention
These data were taken on a 1200W design, but the results should scale to 5kW with similar performance.
I do not understand your last question. I don't know what "...transition of the PFC from the СCM mode to the relay mode..." means. What is "relay mode"? Do you mean change of inductor current from CCM to DCM?
If so, the answer depends on the inductor value and switching frequency. You can calculate the transition point from CCM to DCM by rearranging terms of Equation (42) on page 35 of the UCC28070A datasheet: https://www.ti.com/lit/gpn/UCC28070A
If "relay mode" means something else, then please explain it to me.
I agree:...grounding the CAO of one phase should turn off one inductor,,,and is it necessary to electrically turn off the MOS transistor or not??? The article talks about the compensation scheme,,,where to get it??? Disconnecting a phase under load, “on the go,” will be harmless for inductors and MOS transistors??? thank you,
Sorry, I missed providing that file. This schematic diagram shows how phase-shedding is managed with the UCC28070: 1200W PFC Ctlr & PT Schematics REVE2.PDF It shows a switchable option to disable either Phase-A or Phase-B. Only Phase-A also has the CAOA output pulled to GND on Disable. It is possible to disable the MOSFETs using grounded CAOx only. The gate-driver does not have to have an ENable signal. It is my personal preference to ensure that the driver cannot send gate drive if disabled, regardless of what CAOx is doing.
If the Phase Management method is implemented as described in the article, there should be no problem disconnecting a phase under load, harmless to all components, provided that phase-shedding is done only when the load is less than or equal to 50% of full load.
The essence of the compensation circuit is to double the IMO current and ground the CAO. Did I understand correctly??? I will only remove the phase at light loads to keep the CCM going...the power will be much less than half...if I only turn off the transistor driver and ground the Cao, but don't double the current IMO... The compensation circuit won't work??? Do I need to double current IMO to avoid spikes??? Thank you,
Your understanding is close, but the IMO current is not doubled, it stays the same. The resistance on the IMO pin (Rimo) is doubled in order to double the IMO voltage that is provided to the CAOx amplifiers. When one boost phase is shut down, the current level of the remaining phase must immediately double to avoid a transient disturbance on the PFC output voltage. This is explained in the Phase-Management Demonstration file that I provide earlier.
The "compensation circuit" is the circuit that doubles Rimo. It compensates for the loss of output current from one of two phases by doubling the Vimo signal to the remaining phase, which doubles its current. This change does not happen instantaneously, however on the time scale of the AC line the disturbance on Vout is virtually imperceptible.
Grounding CAOx of the phase that is turned off avoids having a current spike when that phase is turned back on.
Hello. Please give the answer to the ucc28065 controller. if it is calculated at 800 W, how will it behave at loads less than 200 W? Why does it have a minimum load limit of 200 W??? and the ucc28056 has 75 W??? ucc28065 can work on one phase too... Thanks
The UCC28065 is an interleaved transition-mode PFC controller (TM-PFC). 200W is 25% of 800W. This is a light-load condition if the full power design target is 800W. The UCC28065 can easily operate at 200W and lower, either in 2-phase interleaved mode or 1-phase mode. You can program the power level at which the controller changes from 2-phase operation to 1-phase, and vice-versa. It will operate down to 0W and keep Vout regulated. There is no minimum load limit. I don't know why you think it is 200W.
The UCC28056 also can work down to 0W. There is no minimum power limit.
Vitalij, this thread is focused on the UCC28070 controller. If you have questions on the UCC28065 and UCC28056, please start separate E2E threads on each of these, so that each thread can focus on one part. Mixing discussions on several different parts in a thread can become confusing.
Рисунок 9 sluaao8.pdf It shows under what loads which controller is best used. I have a question. Why doesn't the UCC28065 on one phase work with the same efficiency as the UCC28056 on a load less than 200 W? Thank you. I'm sorry, but I can't create a new topic on UCC28065 due to some technical problems.////The specified forum could not be retrieved/// that's why I'm asking the question here... Thank you
Figure 9 of the PFC Selection Guide compares the ranges of full-power for which the devices listed are best suited to control. It does not mean that you cannot use any controller at loads outside of the recommended ranges.
I can't comment on your efficiency question because I don't know what data sets you are comparing. Evaluation results shown in their respective EVM Users Guides indicate that their efficiency curves vs. % of full load are very similar.
I'm not sure what technical problem prevented you from posting. I hope it was a temporary problem. This forum is for simulation and design-tool issues. In general, PFC controller issues and topics can be posted to the Power Management Forum.
Hello Ulrich. Thank you. I am designing a 5.5 kW PFC ucc28070 for an inverter stabilizer at home and would like to figure it out... if the load on the stabilizer is small or very small... What efficiency will this controller have??? I am finishing designing an option where the UCC 28065 controller will work on small loads up to 800 W (first one phase then two phases), and on large loads 800 - 5500 W the UCC28070 controller will work (first one phase then two phases) on the same the same power platform is simply at different frequencies. Please tell me... is it worth implementing this project or not??? Or one ucc28070 controller is enough. Thank you very much
I recommend to use only one PFC converter for your project, using UCC28070. That device is suitable for 5.5kW and can work down to no-load. I think it will be too complicated to combine outputs or alternate between outputs with two different PFC converters.
The efficiency trend for the UCC28070 will typically follow the results found on page 6 of the 300W EVM board User Guide: https://www.ti.com/lit/pdf/sluu312 Although the EVM is only 300W, PFC performance generally stays very similar at higher power because the power stage components are appropriately scaled to match the output power level.
Note: the EVM efficiency results are based on 2-phase operation. 1-phase operation can increase light-load efficiency, but is not implemented on the EVM.
You are changing the topic to dc-dc conversion. Please submit a new E2E request to the Power Management Forum so that the appropriate DC-DC people can help you.
Hello. Please advise. If a rectangular signal formed by 100 Hz PWM with 95% fill and amplitude proportional to the solar battery voltage is applied to the ucc28070 Vacin output... does the ucc28070 "fly" on the solar panel or not, thanks
This question is a spin-off of your previous question 4 days ago for DC-DC step-up from a solar panel. As I replied then, please submit a new E2E request to the Power Management Forum so that the appropriate DC-DC people can help you.
I am locking this thread. For any new issues, please start a new thread.
