• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 701 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM5118: efficiency is decreases with increasing load at buck-boost mode

feanor finvovich
Prodigy 20 points

Hi to all!

I have designed DC-DC converter around this IC with requirements:

input voltage 12-48V

output voltage 24V

output current 2A

Hi to all!

I have designed DC-DC converter around this IC with requirements:

input voltage 12-48V

output voltage 24V

output current 2A

schematic is in the addition

schematic is in the addition

Hi to all!

I have designed DC-DC converter around this IC with requirements:

input voltage 12-48V

output voltage 24V

output current 2A

schematic is in the addition

parameters was calculated with Webench, And I have observed that on 240 mA load at output it have 12V and 0.6A at input and efficency around 80%. When i have put 700mA load consumption current was more than 2 amperes at 14 volts and was increasing with time. At 12V input voltage it cannot start.
Where the mistake?

DC-DC.PDF

  • 0
    TI__Mastermind 21720 points
    Feanor,

    Looking at the schematic:
    1. Some of the components are missing units. Please add those to make the debugging process easier
    2. The output capacitance is seems a little small. It maybe worth increasing the amount of output capacitance.

    So from what I understand at is that at IOUT=240mA the effciency is 80%. This is a reasonable number based on the design parameters. Can you explain the next sentence in more detail? "When i have put 700mA load consumption current was more than 2 amperes at 14 volts and was increasing with time." Does the output voltage drop? Where is the 2A value coming from?

    -Garrett
  • 0 in reply to Garrett Roecker
    Prodigy 20 points

    Thank you for your answer. Missing units is pF. I have solved problem. Problem was in transistors Q5 and Q6 because of it's very large resistance or open channel. They was heated and increase their resistanse. And driver was increase duty cycle to compensate loses more and more. When I replased transistor by other with small Rdson the converter started work stable.