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Spacing of conductorS in primary of offline SMPS?

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grizedale

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Hello,

I wish to use the following 400V TO92 BJT in start-up linear regulator circuit of offline SMPS with Vin=90-265VAC.

https://www.fairchildsemi.com/ds/KS/KSP44.pdf

However, the legs are just 1.27mm apart......and obviously the pads will have rest-rings, -this will mean that the collector and emitter copper will be separated by just 1.8mm......and surely that is below the required minimum spacing of 3mm required for between positive and negative of the rectified DC Bus?

However, i am sure many offline smps use KSP44 in their designs...so how are they getting away with it?
 

For the PCB footprint, you are free to bend the TO-92 pins to achieve the spacing of your choice.

At the case side, you have however 0.8 mm creepage distance between B and C terminal which will hardly comply with most of the existing standards, e.g. IEC 1010, even for the lowest pollution degree. Experience suggests however, that the case side is less susceptible to creepage and flashover than the PCB side.
 
Dear all,
This a good tool for gap max. voltage calculations based on IPC-2222A standard.
Best regards.
 

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  • C4Calc.rar
    101.5 KB · Views: 114
Hi.

I cannot seem to open the RAR file, i was wondering if their is another file liek this but not in RAR format.

-just to show PCB track spacings in the primary of an offline 230VAC smps
 

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