Linkswitch XT2 900V inconsistencies

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Hello,

We've been trying Linkswitch XT2 900V ICs and for transformer design and initial sample configuration we used suggested PIXI design for transformer.
Problem is that with LNK3694G IC it does not seem to be reliable or accurate.

There are several inconsistencies:
In spreadsheet suggested primary is 36AWG but in transformer design it changes to 35AWG
Suggested bias turns results in less than 12V calculated bias voltage. In our test board testing after diode output voltage for bias is well over 20V when adjusted in PIXI to be just above 12V.

Is there a fix planned for this problem?
And should be bias turns used calculated or adjusted to be over 12V?

Attachmentサイズ
LinkSwitch-XT2900V_Flyback_Design3.pdf1.42 MB

Hello DariusP,

Thank you for using Power Integrations in your design. I will try to help you in your inquiries. First, regarding the AWG size, let me review how the differences were arrived at then I'll get back to you on this. Second, regarding the Bias voltage, the bias voltage should just be a ratio between the Bias Turns and Secondary Turns times the Output voltage. In your case, may I ask what was the NBIAS you used when you saw the 20V? Also, what was input voltage in that test and was the 5V Output loaded or unloaded during this time?

Thanks.

Hello,

32T was used to get 12V in spreadsheet and in sample transformer we used calculated value (32T)
At no load it is 12V, at 100mA - 14V, at 500mA - 22V, at 600mA ~24V.
Input voltage - 230VAC
Design is very similar to XT2 datasheet figure8 for bias circuitry, with D1 replaced by S1ML, C3 is 1uF and C4 is 100nF.
Attached schematic of prototype

Our main question remains why PIXI uses two different wire gauges and which to use.

Titleサイズ
LNK3694G.pdf822.22 KB

Hello DariusP,

For the AWG, have you tried making the transformer using AWG35? If it fits, this would be better to use since it would lead to less current density and better thermal performance.

Thanks.

Thank you for your support.
At the moment we only ordered samples, so once we receive them we will test them.