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Questions on HiperPFS Boost PFC controller

Z

zenerbjt

Guest
HiperPFS Boost PFC controllers looks absolutely excellent, but just wish to first check it over..
Please advise on any of these questions….?

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1….TITLE: Setting of Brown in/out threshold depends on set value of vout for Boost PFC?
Hi,
From page 14 of the HiperPFS datasheet it appears (?) that if vout is not set to 385VDC, then the divider to the voltage monitor pin needs adjusting and then this is said to mean a different Brown in and Brown out threshold.

Is this correct? How has the setting of the brown in/brown out threshold got mixed up with the setting of the output voltage?
HiperPFS datasheet:
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2…..TITLE: Max possible Vout of Boost PFC?
Hi
Page 13 of HiperPFS 3 datasheet states that vout of the Boost PFC should never be set to >395V. It is said that there would be a danger of overvoltaging the internal FET during mains transients or load transients

HiperPFS datasheet:

..However, the abs max drain source voltage of the internal FET is 530V. There is a huge output capacitor of at least 100uF on the output of the Boost PFC. So there is no chance of the internal FET getting overvoltaged, even during line and load transients.

So why can we not make the vout say 400V?
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3…..TITLE: Snubber capacitor to safeguard HiperPFS B(Vdss) of 530V?
Hi,
Page 18 of the HiperPFS Boost PFC controller datasheet says that a 33-100pF capacitor should be connected across the Boost PFC diode in order to prevent the internal FET’s B(Vdss) of 530V from being breached.

Page 18 says that the 530V level is most likely to be breached during heavy loading of the Boost output to almost the overload level.

How can such a capacitor be of any use? Surely it would just create more circuit noise due to high di/dt as such a snubber capacitor gets rapidly charged/discharged?

How could the drain of the internal FET go up to 530V?....As soon as the drain voltage goes above Vout then the Boost diode will clamp the drain voltage to vout…..which wouldn’t get anywhere near 530V.

The only way the drain could get up to 530V would be due to PCB trace stray inductance…but this should be minimised with tight layout and having a small value ceramic cap right at the internal boost diode cathode going down to the controller’s star ground point with the power ground.

HiperPFS datasheet:
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4……TITLE: PFC controller uses voltage divider resistors of too high value?…moisture problem?
Hi,
Page 12 of the HiperPFS Boost PFC controller datasheet shows dividers being used for Vout regulation, and also for VAC input detection for Brown in/out monitoring and Input OV detection. The upper resistance of these dividers is greater than 15 MegOhms. This surely is way too high? Slight moisture on these resistors will surely result in false tripping of Input overvoltage detection and poor vout regulation?

HiperPFS datasheet:
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5 TITLE: Why isnt everybody using HiperPFS-3?
HiperPFS-3 gives you boost fet and diode and controller on a single chip, no sense resistor needed, Error amplifier changes dynamics as vout goes outside nominal in order to preserve the output voltage and improve vout regulation…..why is the HiperPFS not the defacto “go-to” chip for Boost PFC today?
HiperPFS datasheet:
 
Last edited by a moderator:
Z

zenerbjt

Guest
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6….TITLE: Can HiperPFS-3 handle a non sinusoidal UPS waveform as attached?

Page 1 of the HiperPFS-3 datasheet states that it has facility to handle distorted input waveforms from UPS. As such, can the HiperPFS handle the attached square wave type output of an UPS?

Would you agree that the lack of Post rectifier bus voltage sensing makes it easier for the HiperPFS -3 to handle “square wave mains”?

The HiperPFS-3 datasheet:
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Z

zenerbjt

Guest
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7....TITLE:.....How do you find the inductor value in a HiperPFS-3 Boost PFC design?
Hi,
Suppose you are doing a Boost PFC for 205-250VAC input, 400V output and 250W power.

Then the way to find the inductor value is to get the switching frequency. Then you design a Boost converter for the Static case of Vin = 205*sqrt(2), and Vout = 400V and Pout = 2*250W. Using the equation Vout/Vin = 1/(1-D) , amongst others, one then assess’s what inductor value gives you the tolerated level of inductor ripple current. Thus you get your inductor value.

….However, one cannot do this with the HiperPFS-3, because you have no way of knowing what the switching frequency will be.

There is a graph on page 7 of the HiperPFS-3 datasheet (Fig9a) which shows switching frequency at mains peak for various mains input voltages….but it does not give switching frequency for 205VAC. Also, Fig9a must only be relevant for a particular value of Vout, but fig9a does not say what this vout value is.

So how do you calculate the needed Boost PFC inductance value for HiperPFS-3?

HiperPFS-3 Boost PFC controller datasheet:
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Z

zenerbjt

Guest
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8.... TITLE:…How can you set the peak current limit on hiperPFS4?
The voltage monitor pin divider ratio affects the peak power limit. How does this happen? How can we set a peak current limit for the FET switch?
How can we bypass the Voltage monitor pin? We want to bypass it because we want to set our own brown out threshold.
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Z

zenerbjt

Guest
hi. Qu 7 now answered...it comes out in the PI Expert software from power integrations
 

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