Hyper PLC810-boost diode and crest factor.
Hi I'm looking for some possible cause of a problem on the PFC stage of the 810.
The supply is a 300W LLC. I am only running the PFC stage currently at 340VDC (I know it is low but my electronic load is only rated for 360VDC.
The problem I am getting is that the boost diode keeps popping. It a HFA04SD60SPBF. 4A. The PFC choke has been designed on pi-expert and it 750uH.
The core is an RM12 so plenty of gap and material. I just can seen the core saturating???
Vin is 220V.
Before the diode popped the AC rms current had a good crest factor but the peak of the AC current has several large spikes as if the PFC choke was going into saturation. I think this is what popped the diode but I'm not completey sure.
I can up rate the diode but the current spike is what I'm concerned about.
Any ideas?
MKD
Comments
Hi Tucker
I have attached the PIXLS sheet. The value of the inductor was initially 340uH but I have increased it to 750uH to reduce the PFC switching currents. I have down graded the input spec to 195-265Vac.
The AC wave shaping is better but there are still a couple of large spike on the the peak of the AC current and the Zero crossing point. I dont want to shove to much power through it until I have a clean AC wave shape. I have slowed the on time of the PFC FET which has helped but I am thinking that it could be the loop compensation as I am running at a lower output voltage than designed for?
The current sense resistor is 0.5R.
I am assuming that the voltage on the ISP pin should not exceed the 0.5V current limit under normal operation?
I have now picked up another problem while testing the LLC stage. The Bootstrap resitor for the VCCHB pin 10R is over heating and shorting. Even when on no load. The switching fets are FCB20N60. I will try slowing them down.
Any thoughts?
MKDA
MKD
If your minimum input voltage is 195 VAC then pls. change the spreadsheet input to 195 VAC.
The spreadsheet will tell you if you are saturating.
Also you can look at the inductor current and zoom in on the current where is spikes up high.
If your ISP current sense resistor is 0.5 ohms, then the choke current will not exceed 1 A. This is too low for 300W and 195VAC.
Redo the spreadsheet. Enter the PFC core you are using. Adjust the Krp value in the PFC section until you get the inductance you want. Note the number of turns required and the peak flux density, and required ISP sense resistor. If you build it with fewer turns than recommended, your core will saturate.
If I only adjust the KRP value the choke is always in saturation.
If I adjust the BP down then I get a similar design to the choke I am currently using see sheet.
Are you suggesting that I only use KRP to adjust choke values as I will need a bigger ferrite core.
Can you post a completed PIXILS sheet so that I can work back from that or can you review my attached sheet.
I cant zoom in on the current wave shape dont have a fast enough scope.
I can only follow the general wave shape using an AC current probe.
The RSENSE on the previous post should have been 0.05R 2x0.1R
How many turns does your ferrite RM12 choke have and what inductance is it gapped to?
Hi
The PFC choke is on a RM12 using 3C90 cores.
Primary winding is 60 turns trifilar 0.4 TIW. With a 4 turn bias winding to power chip (not connected currently)
LP=740uH measured @ 1kHz.
Vin 195-265V
K=0.4
Rsense= 0.09+0.09= 0.18R.
CBULK= 220uF
I am running the PFC at 340V with an electronic load.
The required spec is actually 85-265VAC I've down graded the spec until I get the PSU running properly.
Pls. post the PIXLS file.