Hello,

I am about to design LLC resonant converter with ADP1046A.

Capacity: 1.5kW(Ir = 5A, V=300V)

Lm is decided from turn ratio.

PWM switching frequency: 100.8kHz

1. Cr value that I am using is 2.2uF. But I would like to know how to find the best C value.

2. To find Lr value, which formula of two yellow boxes do I need to use?

3. I would appreicate if any tip or advice for LLC resonant converter desing is given.

Best Regads,

Mack

Hi Mack,

It really depends how low the input voltage goes and the range (min-max) of the input voltage. It's better if it's a tight range. The turns ratio of the transformer also depends on it. For this calculation I assumed Vmin= 380VDC.

You need to use the formula Cr= 1/(Lr*(2*pi*f0)^2) which is formula for fr1 as per your diagram. You should double check your capacitor value as 2.2uF is too large and will yield a Lr value of 1.1uH only which is too small. I suggest you keep the Cr value in the nF range. Again it depends on how much gain is needed at lowest Vin. Let me know this information and I can suggest something more.

If you want a good article on resonant LLC control please refer to this. It is not a design document but gives insights into the LLC topology.

http://www.edn.com/design/power-management/4438766/High-efficiency-resonant-mode-implementation-using-digital-control

Lt Comm Data