DI-80 Design
I would like to use the DI-80 buck regulator design for a project. My input range is from 120 to 277VAC. I assume the only changes necessary are the input filter capacitors, rate to 450VDC and maybe bump the rectifiers to 1N4007 devices.
This design was very appealing to me as it looks like agency approvals have been met already. I would like to know if you offer any kind of review on the PCB? I have my layout complete and it would be great to know if something simple was overlooked on my end.
Comments
Hi -
I have my prototype board built up and it is not working properly. The output fluctuates between ~45 to 155VDC. I do not have U2 or C6 populated yet. I have checked the schematic as well as my PCB layout and can not see the problem. I will increase C4 to 10uF to see if that helps. Could you look over my schematic and offer your advice?
Hi,
From your description it appears that the IC is switching but the circuit is unable to maintain regulation.
This appears to be a problem related to the feedback circuit. The value of capacitor C4 needs to be increased to at least 10uF. Please see circuit example Figure.5 in our data sheet on page 4.
Without a sufficiently large capacitor in the feedback circuit, the feedback pin voltage will drop, forcing the Link Switch IC to switch which will result in excess voltage at the output in the absence of any load.
Kindly verify the value of feedback circuit components in your design.
Regards
PI-Sarek
Hi Sarek -
I have changed the value of C4 to 10uF and it still just passes 161VDC with no regulation. I have also put two 1mH inductors in series thinking that the peak switch current may be causing this. Should I try a 22uF capacitor next? I am using tantalums, if that matters.
Hi,
I suggest you use a 10uF Al-electrolytic for C4 for now.
Your description suggests that the IC fails to receive any feedback. You could check your feedback circuit by connecting an external 12V bench supply across C4 and measure the voltage between the feedback "FB" and the source pin "S". This voltage should be approximately 1.65V.
One other situation in which you may experience this problem is if there is no pre load present at the output(resistor R4 in our example circuit shown in Figure.5 on page 4 of the LNK-TN datasheet). Please verify the value of this resistor.
Please also verify if you continue to experience this problem even when you connect a load. You could do this by connecting a resistive load at the output across resistor R4. A resistor value of 100 ohm will present full load and dissipate approximately 1.44W.
I hope this helps you to resolve the problem with your circuit.
Regards
PI-Sarek
Hi -
I have changed the value of C4 to 22uF and it is still not regulating. The schematic is the same as the DI-80 Design Idea so I am puzzled as to why it is not working properly. I have attached the layout files for your review as well.
Hi,
Let me know what you find regarding the two other suggestions I maid in my previous reply:
1. Feedback circuit check using external bench supply
2. Operation of circuit with load (resistive load).
Regards
PI-Sarek
Hi Sarek -
My load resistor appeared to be opened, I replaced it with another 3.3K device and the circuit is now working fine.
Thanks for your help it is truly appreciated!
Hi,
For the DI-80 design, you are right about the fact that you can use high voltage capacitors at the input and meet the higher input voltage (277VAC) requirement.
As regards layout, please follow the guidelines that we provide in our datasheet.
Different safety agencies and applicable safety standards have different creepage and clearance requirements. A safety agency inspector or safety engineer should be able to help you with evaluation for compliance for the specific safety standards you are trying to meet for your design.
If you need an engineer to provide preliminary feedback regarding your layout, please post your layout and schematic on our forum and we will be happy to review.
Regards
PI-Sarek