Buck Converter Design, Problems Problems and Failures!! :(

[Mustafatarhan49]

I have been working on a DC DC buck converter. I have faced with a lot of problem. I really need your help. I will post the problems that I have up to now. So may be you can comment it.

- I need help for high side gate driving circuit, I searched about bootstrap capacitor but I did not understand at all.
- I need help for the feedback loop- Any help how to do that?
-Component selections=> I have found many website and read many article but each time I got different values.

To inform that I used parameters such Vin:50V Vout:5volt Iout =30mA fswitch =100~150kHz
Any schematic or other things will be perfect!

 

[BradtheRad]

Your coil's henry value and the operating frequency go hand in hand. Use the inductive time constant formula as a guide (L/R). For 100 kHz to 150 kHz, start out with a coil value between 1 uH and 100 uH.

The smoothing capacitor can be in the same ballpark value of uF. You can increase or decrease depending on how much ripple you can allow.

Here is a link to a thread discussing switched-coil supplies. I posted a link to an animated simulation of a simple buck converter. It is user-interactive and will run on your computer.

https://www.edaboard.com/threads/268178/

 

[xyxfox]

hey, pal
feedback loop's design is after power train design. should choose voltage mode control or current mode control at first. then get the transfer function of power train. find out the worst case working condition. at last set coner frequency for poles and zeros. TI's application note named "Understanding Buck Power Stages In Switchmode Power Supplies" is helpful to you.

 

[goldsmith]

Hi Mustafa Rahman

- I need help for high side gate driving circuit, I searched about bootstrap capacitor but I did not understand at all.

A short answer : boot strap method in a float driver , just plays a simple role ! it will be charged and will be discharged into the GS junction ! thus your mosfet or IGBT will work in on / off region ( as a perfect switch ! )

- I need help for the feedback loop- Any help how to do that?

What kind of driver you are using ? ( how you have created PWM signal ? with usual drivers or perhaps your own way ? ) for judgment regarding this issue more informations from your side is required .

-Component selections=> I have found many website and read many article but each time I got different values.

What kind of component ? mosfet ? floating driver ? ferrite core ? ... etc

Best Wishes
Goldsmith