200W PFC Front End design question

Posted by: dale.stepps@gm… on 06/20/2014

Hi Everyone,

Here is my question. I have a PFC design using the HiperPFS2 and the unit will start up under load hold for 5 seconds then shutdown. The output voltage hits target but can't maintain.

Normal compensation network. Input voltage held constant. Load constant 200 watts.

What mechanism in the chip would exhibit this behavior?

Thanks ahead of time for response.

Dale

Comments

A poor thermal connection to the heatsink can cause this symptom. The device hits thermal shutdown.

Hi,

The loose thermal connection was the issue. Thanks for helping.

Now I have another question. The PFC frontend works fine with 400VDC output at 265vac DOWN TO 227vaC but then the PFC falls off and THD goes up. My thinking is that the HiperLCS2 needs beefing and or inductor and capacitor. It seems the stage has enough energy to boost the higher voltages but not enough for lower voltages.

The PI tool does not allow interaction. There is just a fixed 350W design there.

Any thoughts? 400uH inductor, 330uF, and HiperLCS2 7326H part for the moment.

Thanks,

Dale

PI-XLS allows you to change the load power, of course. What version do you have? Did you run the "check for latest version"?

Pls. post a snapshot of the inductor current when it is distorting, with about 2 ms/div.

Thanks for previous help. I did get the latest version of PXI and it does allow for cahnging the power. What I have noticved is that the inductor values are way off. When I actually build units with the calc inductor nothing works. So I wonder you guys have actually build boards using the PXi tool.

Here is what is happening: The Hiper regulates the target voltage (400V) fine at all input voltages if I start at 265VAC and then variac down, but has the following problems:

1: It does not want to start up consistently at 120VAC.

2. The unit maintains target voltage but does not PFC and has high THD. Why would it regulate and not PFC? What components effect one but not the other. It seems to me if it is regualting then it should be PFCing the power.

My questions are: What is important at the 120VAC startup that the high voltage takes care of? Are we violating some start-up sequence parameter, if so which one? Why are the inductors calculated far too large? Basically we have to just try and see waht works.

Please help, under the gun to get this going.

Thanks,

Dale

Are you using a ferrite, Koolmu/Sendust, or iron powder core?

Pls. post scope pics of :
- inductor current with 5 ms/div of condition 2 you typed

- for condition 1, inductor current and output voltage, at 5 ms/div, starting at the first pulse, for a case where it started

- and a case where it didn't

Are you using a ferrite, Koolmu/Sendust, or iron powder core?

Pls. post scope pics of :
- inductor current with 5 ms/div of condition 2 you typed

- for condition 1, inductor current and output voltage, at 5 ms/div, starting at the first pulse, for a case where it started

- and a case where it didn't