LM2679: Variable Power Supply. LM267x Made Simple

Hannes Meyer

Prodigy 100 points

Part Number: LM2679

Hello,

i am trying to design a variable power supply with the LM2679. It would be great if i get 1-30V at the Output.

In the Datasheet they write about the program LM267x Made simple, but I do not find that.

My problem is that I do not know how to decide which parts I actual need.

Is this project even possible?

Thank you for your answers.

Hannes

over 7 years ago

0 Ambreesh Tripathi over 7 years ago

TI__Expert 6860 points

Hi Hannes ,

You can use Webench designer for your application .
Further LM2679 is a voltage mode control device switching at 250KHz and should be able to handle smaller on time (lower duty cycle ratios) needs of your application .
Also the ref voltage of LM2679 is 1.25V so you can vary output between 1.25V-30V .

---Ambreesh

0 Hannes Meyer over 7 years ago in reply to Ambreesh Tripathi

Prodigy 100 points

The simulation shows that I have to change the inductance if I change the output voltage. Do I can adjust the voltage just with the Feedback resistors?

0 Ambreesh Tripathi over 7 years ago in reply to Hannes Meyer

TI__Expert 6860 points

You can add a third resistor on the feedback network and change the voltage there to modify the output .
Further LM2679 is internally compensated and in order to ensure stable operation over your wide range of input and output , you would need to do extensive bench testing as well as simulation .

---Ambreesh

0 Hannes Meyer over 7 years ago in reply to Ambreesh Tripathi

Prodigy 100 points

ok I simulated it like this: webench.ti.com/.../SDP.cgi
Is in right and which value do I need for the resistor and in what place does it has to built in?

0 Ambreesh Tripathi over 7 years ago in reply to Hannes Meyer

TI__Expert 6860 points

0 Hannes Meyer over 7 years ago in reply to Ambreesh Tripathi

Prodigy 100 points

First thank you very much.

So, is it right that i can set the voltage just at 1.21V and 30V. My purpose ist that I want to build a lab bench power supply.

Sorry for my missing knowledge I am an electronics student from germany.

0 Ambreesh Tripathi over 7 years ago in reply to Hannes Meyer

TI__Expert 6860 points

Hannes,

You can get any voltage between 1.21V to 30V . you need to add a ref voltage between 1.21V to 3.3V at other end of Rmod as shown in pic in my earlier thread . You can easily generate the ref voltage by programming a GPIO of a controller to output variable duty cycle and then peak detect the same .

---Ambreesh

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LM2679: Variable Power Supply. LM267x Made Simple