High Power Synchronous Buck Converter using KA3525 - Page 1
Forum section: electronics / projects

author: Swaroop 21
author_rank: Regular Contributor
timestamp: August 18, 2024, 05:15:04 pm
content: Hiii, I am designing a Synchronous Buck Converter using KA3525 and IR2110 IC for driving the MOSFETs which are IRFP250N. Didn't Find any proper synchronous buck converter, As some boost converter or dc to ac inverter are common. So I have just put together the schematic with datasheet and some individual circuits from the net. Anyways, the input is around 60V DC and can supply 8Amps. I have attached a .pdf of a example Schematic that I made. The switching frequency should be adjustable from 45Khz to 70Khz. Inductor is the Ferrite Ring (Yellow coloured) from the common output filter from a computer power supply the two toroid are placed together and then wound a few turns to be around 80uH.I have a few concerns.1. Is the output stage section correct ?2. What should be the value for the bootstrap capacitor for IR2110 for driving the mosfets at the mentioned frequency. I have use standard value of 1uF for now.3. (IMP) What should be the dead time resistor on the KA3525 to make the mosfets switch correctly and not overlap the signal ?Please give suggestions on how to improve the design, Component Values. This is not a final schematic just to post it here for review. I tried a few designs with the 3525 IC but have not got good results maybe just because of configuration error. I hope this time I get it right.Schematic_High-Power-Buck-Converter_2024-08-18.pdf(99.81 kB - downloaded 93 times.)

author: Kurets
author_rank: Regular Contributor
timestamp: August 18, 2024, 08:56:57 pm
content: The schematic drawing style of using net labels and ports to connect things which are next to each other ruins readability.80uH seems too low for your targeted switching frequency. You don't state the targeted output voltage but your output divider seems to indicate around 50V (internal vref of KA3525 is 5-ish volts which you multiply by between 20 and about 7). Whichever way you will have several amps of current ripple in your inductor which will cause a lot of dissipation.I also think that your bootstrap capacitor is not tied to the switch node.Sceptical about the soft start relay circuit, just damping the input filter can solve any ringing issues upon connection of supply. And, I suspect that if your supply is some other DCDC, then it will have its own softstart anyway.My advice is to find a dedicated synchronous buck driver chip and use the datasheet example calculations to figure out a starting point for your design.

author: Swaroop 21
author_rank: Regular Contributor
timestamp: August 19, 2024, 05:09:28 am
content: Quote from: Kurets on August 18, 2024, 08:56:57 pmOhh Yes, I noticed now that the VS node of the bootstrap is not connected sorry for that. And I am powering this from a 48V 8Amp Transformer, the softstart is just to avoid sparks when connecting the circuit or when I use relay to switch the power rail it will weld itself if its not properly rated.Yes I am looking for IC available here which will do the job but just I had many 3525s I just though using them would be a good choice.