UCC28631: Preload

Linh

Prodigy 40 points

Part Number: UCC28631

Hello,

I have the following design using a UCC28631.

Vnom: 270V

Vout: Multiple

Po:80W.

The device needs a minimum preload value from Eqn 64 in datasheet, PPRELOADmin = 0.5 × LPRI× (VCS:min / RCS)^2 × fSW:min , but for my design to work I have to set my outputs preloads to almost 10W!

My Lpri is 250uH (similar to the example equation) and my Rcs is 10 Ohms ( .2 Ohm going through 50:1 CT).

over 5 years ago

0 Hong Huang over 5 years ago

TI__Mastermind 47295 points

What is the rated power together from all multiple Vout? Also, did you use the excel calculator when making this design?

0 Hong Huang over 5 years ago in reply to Hong Huang

TI__Mastermind 47295 points

Noticed 80W total power. So the remaining question: did you use the excel calculator when making the design, if not can you use the calculator to check your design to see where need to modify?

0 Linh over 5 years ago in reply to Hong Huang

Prodigy 40 points

I did use the Excel Calc. Another question - since I am designing for multiple outputs...which output value should I put in the excel since that will affect my Rcs and Lpri.

0 Hong Huang over 5 years ago in reply to Linh

TI__Mastermind 47295 points

Can you provide all output voltages and currents so for me to provide my suggestion?

0 Linh over 5 years ago in reply to Hong Huang

Prodigy 40 points

The outputs are:
V I
12 0.75
32 1.2
12 1.75
16 0.65

0 Hong Huang over 5 years ago in reply to Linh

TI__Mastermind 47295 points

My suggestion is use Vout = 32V and pretend all power 80W on the 32 V output to calculate all primary parameters.

On PSR (primary side regulation) such as using UCC28631, please refer this blog article for transformer winding stack if applicable to your design:

e2e.ti.com/.../designing-multiple-output-converters-with-primary-side-sensing

Power management

Power management forum

UCC28631: Preload