power supply with LNK306GN

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Hello, I am developing a buck-type power source with LNK306GN from 12vdc to 300mA, what voltage should I measure from the common of the source to physical ground? It is normal to be measuring 60 vrms.

Hi Arkan,

Could you please provide a picture of your test setup with the point of measurement?

Best Regards,

hello PI-Yoda

Annex schematic diagram of the source of power that we are developing and the points where I am taking the measurement, I just want to know if Is the value of this measurement normal and why?

Power_source_schematic.png20.34 KB

Hi Arkan,

There far too many unknowns for accurate prediction of the measured value. Detailed investigation has to include:
- mains and and DC side connections
where and how the earth line is connected to neutral line
where the symbol "earth" in the right bottom part of your schematics is connected.
- symmetry of the measured signal value (from + and - of the DC)
- load dependence of the measured value - indication of HF or 60Hz signal is measured
- the actual multimeter parameters used for the measurement ( Input impedance, frequency band, rms converter type) - because it takes part in the circuit with its input impedance and the read values are dependent of the performance of the actual device
- other mains supplied measuring equipment connected to the circuit. Electronic load?
- input capacitors ESRs,
- CM filter symmetry.. etc, etc.
Similar effect could be observed via simulation. I am attaching a picture from a possible starting point model.
The complexity could be increased with more realistic modelling of the components and adding the high frequency noise induced in the ESR deferentially and to earth through common mode capacities path.
Best Regards,

Hi, PI-Yoda

Thank you very much for your attention, and you could attach me the image you mentioned to me, and in what you could see from the diagram of the power source, it is correctly implemented according to your experience, they are data that I took from your application notes. .

and again thank you very much ..

Sorry Arkan, the picture did not load the first time. Now should be attached.
If you are satisfied with the performance of your prototype and EMI is good you should not worry about that voltage.

Capture.PNG132.11 KB

hello PI-Yoda
Thank you for answering my questions and giving me the necessary information,
I would like to know about the source we talked about earlier, what would happen if for some reason I wanted to use it to power a card with a microcontroller, and that this in turn had a connection to the computer, and since the computers have Your common voltage source (V-) connected to physical ground, would there be any problem in the connection, because of the voltage that I measured from the common of my power source to physical ground?

Arckan, you cannot connect directly any point of the full bridge rectified mains to Earth !
In the three lines mains supply the Earth is connected to Neutral some were down the supply line and this will cause a short in your bridge rectifier.
Usually the computer uses isolated power supply where the secondary is connected to Earth. You also need to build isolated power supply to be able to connect its secondary side to Earth.

I wold advise you to visit our local representatives where the technical team will recommend the best topology to suit your application.

hello PI-Yoda

Thank you very much for your response, I will verify the implementation of an isolated source, the application in which we want to use this source is in an appliance, do you think it might be appropriate to use this type of source in it?
thanks again

Hi Arkan,
The tiny bits and pieces I saw and understood from you project
- 12V, non-insulated from mains power supply (with direct Earth connection?!)
- Used for computer card
- In appliance
does not allow me to provide advice.
Some appliances have ‘mains side’ electronics not accessible for the final user where only functional isolation is required. Some appliances are completely secondary side electronics driven where the SMPS or transformer takes care of the reinforced insulation required by the safety regulations. Some appliances have both.
The additional source of power in (assuming household) appliance MUST be introduced in accordance with the total concept of safety for that appliance. That means - all aspects of the specification you are working on needs to be carefully considered in order the solution to comply with the standards.