LCS708 Kratio=1 not accepted. I need it for wide output range

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I am using PI Suite,

I need wide output regulation range with a shorter frequency range.

I selected Lmag= 100uH , Lres=100uH

I have seperate cores. One for Lres and one for Transformer.

My Kratio=1, But the PI suite requires a minmum value of 2.1 for the Kratio.

Is there a reason why the software limit Kratio>2.1

Best regards.

Hi rxpu,

Too much Low Kratio will result to higher magnetizing current and less efficient design/higher thermals. It will not meet rated power capability of our LCS part when you use lower than recommended Kratio. You can technically use your desired Kratio of 1 but you need to use bigger part. Unfortunately you are already planning to use the biggest part. Just try to cool down the part by increasing heatsink. May I know what is your output power requirement, regulation range and input range?

I need to design a variable output voltage between 0..10V. My design power is 400W, But according to your recommendations I should lower my design power to meet the power handling requirements of the switching mosfets.

As I understand I have 2 choices to try to reach this wide output voltage operating range

1- Lower Kratio to 1, But as you said the circulating current increases (so as the input rms current on mosfets). So I decrease the design power to 300W-350W and use a Kratio of 1.

2- Keep the Kratio as 2.1. Design power is again 300W-350W. But I use a broader frequency range to reach wide output voltage. What I gain by increasing the Kratio , will be spent as the swicthing loss on mosfets for a broader frequency range. The organisation/limitation of pulse skipping (or maybe disabling it) is here a question.

Would you go to the direction 1 or 2 ? Through which way can I get more output power from LCS708.

Best regards.

Hi rxpu,

You will have better efficiency at 2.1 Kratio and it might already enough to cover your wide output range. Start your prototype with 2.1 Kratio then do necessary adjustment when you have the initial data.