Output voltage does not output correctly
I made a board using Power Integrations' ACDC converter (LNK302D).
There is only one that does not output the output voltage correctly, and the voltage of about + 14V is output at the design value of about + 12V.
As a load, an operational amplifier circuit of about 4mA and a resistance load of 5.1KΩ are attached.
So when I was looking at the waveform of each part with an oscilloscope,
I happened to see the voltage between the FB pin and GND
I noticed that when I connected an oscilloscope, the voltage became about + 12V.
So, when I connected a 22pF ceramic capacitor between the FB pin and GND, estimated from the oscilloscope equivalent circuit, the voltage became stable at about + 12V.
I couldn't figure out what was the cause of this by looking at the data sheet, so could you please tell me?
Comments
1. No. It works only under the conditions of the question.
2. Although they are not exactly the same, the arrangement of parts is similar.
The input circuit of D pin is a little different, but the circuit around S / BP / FB other than that is almost the same as the data sheet.
About 120V is input to the D pin, which is smoothed with a capacitor. The other boards are outputting the correct output voltage.
Hi nnn saito,
Good day to you and thank you for providing more information.
The output voltage for device LNK302D is only controlled by the resistor divider network in the FB pin. Having known that an oscilloscope probe or adding a capacitor across fb pin changes the output, it is an indication that noise is being coupled to that pin.
We suggest that you follow our recommended PCB layout in in page 5, figure 6b on the product datasheet: linkswitch-tn_family_datasheet.pdf (power.com)
You may also check ‘Recommended Layout considerations’ on page 12 of this application note for additional reference (an37.pdf (power.com))
We hope this resolves your concern. Please let me know if you need further help. Thank you.
Can we ask for your schematic design?
Question:
1. Did you experience the 14 V output during no-load and full load?
2. Did you follow the recommended PCB layout in the data sheet?
We hope you can provide this information because it will really help us to solve the issue. Thank you very much.