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HI to all,
We have slightly modified the design .
The RCD snubber was modified (we used 20k resistance) and output filter as well . (higher inductor value and more capacitance)
One issue we have, on 1A our voltage output is 5.35A , 2A , its 5.1V and 3A we have 4.2V
Is it a correct to assume that this is a optocopler feedback issue ? What should we modify on it.
Thank you
Andre
Andre, could you list all of the modifications on your design? Meanwhile, is it possible to see the output voltage? We would like to know whether the output voltage is stable. Thanks!
Andre, I don’t think changing higher accurate resistor can help to fix this unless the current resistors have bad TCR, which means the resistance would change much with the temperature. Can this issue be observed on other boards? If they are the same, it should be not caused by the FB resistors.
I am think where the feedback point connects to? Before the inductor? If so, that’s normal since the DCR of the inductor will cause a DC voltage drop with the increased load current.
Ok, Andre. That makes sense. The voltage difference is caused by the DCR of the inductor in this design. You can try to select one with as low as possible DCR for this if you don't want change the feedback point. If the feedback point is connected after inductor, the close loop would be taken care since the LC stage is involved in the close loop and will introduce a dual-pole at 1/(2*pi*(L*C)exp*1/2). Larger inductor generates lower pole frequency which may make the close loop unstable easily.
Hi, Andre
We cannot see the figure clearly. Could you please send this figure via mail to us (yingyang.ou@ti.com)? BTW, please also help to capture the voltage ripple monitored by oscillation via the voltage probe. Thanks!
Hi, Andre
Sorry, I typed a wrong mail address. Please re-send it to yingyang-ou@ti.com. Thanks!