TI-PMLK Buck-Boost Experiment Board using LM5118

Donglun Li

The question is about the experiment 1 of the PMLK Buck-Boost Experiment Book (Rev. A). It says when calculating the Duty-cycle of mode CCM, we need to find the converter efficiency. And there is a table for theory values. Actually, how can i know the Iin(input current) to get Pin in theory?

over 6 years ago

0 Helen chen over 6 years ago

TI__Mastermind 40080 points

Hi Donglun,

The experts of this part is in US. They will reply you one days later.

For the Pin, it is determined by the output power and the conversion efficiency. So Pin=Po/eff. =(Vo*Io)/eff.

0 Donglun Li over 6 years ago in reply to Helen chen

Prodigy 180 points

yeah the output power is easily calculated.But how can I get the efficiency?

0 Garrett Roecker over 6 years ago in reply to Donglun Li

TI__Mastermind 21720 points

Hello Donglun,

To calculate the efficiency there are four parameters that need to be measured. {VIN, IIN, VOUT, IOUT).

The input current and output current should be measured with an ammeter. The voltages should be measured with a DMM directly at the board.
Input power is calculated at VIN*IIN and the output power is calculated as VOUT*IOUT. Efficiency is then calculated as POUT/PIN.

Thanks,

Garrett

0 Donglun Li over 6 years ago in reply to Garrett Roecker

Prodigy 180 points

But I mean to the theory efficiency. Because there are values for theory to be calculated in the given table.

0 Garrett Roecker over 6 years ago in reply to Donglun Li

TI__Mastermind 21720 points

Hi Donglun,

I'm not sure what table you are referring to.

To estimate the efficiency and number of things need to be taken into account. Such as the switching loss and condition losses of the MOSFET.

Thanks,

Garrett

0 Donglun Li over 6 years ago in reply to Garrett Roecker

Prodigy 180 points

It is the table at page 27 of experiment1 test1. You can see there is a parameter for theory duty cycle. But there is no formula for theory duty cycle in CCM by theory background.

0 Donglun Li over 6 years ago in reply to Garrett Roecker

Prodigy 180 points

And also at Page23 there is table1 for the expressions of duty-cycle, inductor current slopes, dc average, peak and valley values in CCM for the converter in Buck Mode and in Buck-Boost Mode. Is there any table for the DCM mode? Because I want to work out the formula(3)-(8) by myself.

0 Garrett Roecker over 6 years ago in reply to Donglun Li

TI__Mastermind 21720 points

Donglun,

It looks like there is not a table in the book regarding the DCM operation duty cycle values. These can be derived using the voltage second balance of the inductor.

Thanks,

Garrett

0 Donglun Li over 6 years ago in reply to Garrett Roecker

Prodigy 180 points

What about the duty cycle in CCM operation? According to page 23, the duty cycle in theory can not be calculated due to unknown efficiency.

0 Garrett Roecker over 6 years ago in reply to Donglun Li

TI__Mastermind 21720 points

Donglun,

CCM operation duty cycle can be calculated using volt second balance of the inductor. This is the ideal calculation for duty cycle and can be used to calculate efficiency. Efficiency will change the duty cycle slightly.

Thanks,

Garrett

0 Donglun Li over 6 years ago in reply to Garrett Roecker

Prodigy 180 points

Thanks for your suggestions. I have already solved it. What about page 35? there is a table for power losses in four different modes. Could suggest me how to Launch formula?

0 Garrett Roecker over 6 years ago in reply to Donglun Li

TI__Mastermind 21720 points

Hi Donglun,

What do you mean by launch formulas?
Thanks,
Garrett

0 Donglun Li over 6 years ago in reply to Garrett Roecker

Prodigy 180 points

sorry, it is Equation derivation.

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TI-PMLK Buck-Boost Experiment Board using LM5118