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The output voltage of LNK564 chip is unstable and uneven in mass production.

Posted by: hezhe on Fri, 12/11/2020

Pi Engineering: Hello! About LNK564 in mass production. It is found that the output voltage of the chip is unstable, there is no constant current and constant voltage, and the output voltage error is very large. And loud. The high-frequency parameters were previously calculated by engineers at Pi. Output 8.1 v 0.3 a using EE16 hf. R 147K1% r 23k1% see annex. Then with the high-frequency manufacturers, check the high-frequency production process and leakage inductance. The high-frequency production process has also been improved. But the result was the same. Can you run the high-frequency parameters again for me.

Comments

Submitted by PI-Martok on Sun, 12/20/2020

Hi Hezhe,
Thanks for using PI product. As per my understanding on your query, the issue is voltage and current regulation stability during mass production. Can you give me some production data or more details about the issue?

Submitted by hezhe on Wed, 12/23/2020

Hi PI-Martok this chip is a pre-approved by an old client. Before the number of products is not a lot, a small problem is also easy to handle. As the number of customers increases,. Bad products also with the Mengzeng. 30% of the time. The original high-frequency Output Voltage 8V. Consider component errors in the production process. The actual output of 7.8-8.2 V is acceptable.
20% of 30% of the defective products have an output voltage of 7-7.5 v. There is a 10% output voltage between 8.4 V-8.8 V. The circuit boards with high output voltage and low output voltage will be interchanged at high frequency. The output voltage of both defective parts is between 7.8 v and 8.2 v. If the output voltage does not reach 7.8-8.2 V, then replace the LNK564 chip. The output voltage of this circuit board is normal after replacement. This chip is a linear constant current constant voltage chip, the output is a bit error. But in our production, such a big error is not right. We've had PI engineers working with us before, and we've had the same results from the high-frequency vendors.
So I'm wondering if the HF and the chip are a match. Last time it was uploaded, it was a high frequency calculated by Pi Engineering

Submitted by hezhe on Wed, 12/23/2020

Hi PI-Martok this chip is a pre-approved by an old client. Before the number of products is not a lot, a small problem is also easy to handle. As the number of customers increases,. Bad products also with the Mengzeng. 30% of the time. The original high-frequency Output Voltage 8V. Consider component errors in the production process. The actual output of 7.8-8.2 V is acceptable.
20% of 30% of the defective products have an output voltage of 7-7.5 v. There is a 10% output voltage between 8.4 V-8.8 V. The circuit boards with high output voltage and low output voltage will be interchanged at high frequency. The output voltage of both defective parts is between 7.8 v and 8.2 v. If the output voltage does not reach 7.8-8.2 V, then replace the LNK564 chip. The output voltage of this circuit board is normal after replacement. This chip is a linear constant current constant voltage chip, the output is a bit error. But in our production, such a big error is not right. We've had PI engineers working with us before, and we've had the same results from the high-frequency vendors.
So I'm wondering if the HF and the chip are a match. Last time it was uploaded, it was a high frequency calculated by Pi Engineering

Submitted by PI-Martok on Sat, 12/26/2020

Hi Hezhe,
Your power supply output voltage range requirement (7.8-8.2V or +/-2.5%) is a little bit tight for LNK564. As per data sheet of LNK564, its FB regulation range alone is around +/-5.32% or 7.6V-8.4V output voltage production swing. Adding the tolerance factor of transformer leakage inductance and voltage divider resistor would make the mass production yield to roughly around +/-8%.
- To minimize the factor of transformer leakage inductance, Please try to add leakage suppression resistor in series with the auxiliary diode before the aux filter cap. This will minimized the voltage variation due to leakage inductance
- Kindly also send your circuit diagram ?
- For high volume production Issue, Please also try to contact our local Field Application Engineer.

Submitted by hezhe on Mon, 12/28/2020

Hi PI-Martok, I worked with the local field engineers a long time ago. He helped calculate the high-frequency parameters. I'll upload the schematics.Thank you... for the answer

Attachment Size
A817M-L.pdf 50.98 KB
Submitted by PI-Martok on Mon, 01/04/2021

Hi Hezhe,
Thanks for sharing your schematic.
From the schematic point of view, Have you tried connecting the feedback resistor across the bias capacitor C7? I was thinking the voltage across C7 is more stable than on the bias winding.
Also implementing trimming resistors on FB would be more cost effective than replacing the IC. Group the units with low output voltage and high output voltage then apply corresponding trimming resistor by just removing parallel resistor across R9 or R11 to center the output voltage.