Trouble with 3V3 supply

Dear support team,
I see no answer so I try to better explain the problem. I design the Ac/dc power supply with your PE tool ( Vin 230 V

Vout 3V3 @ 300 mA ) . When I built and test the design, I notice that without load the output is a stable

3.5 V . When I load the circuit with a resistor array, the output fall to a noisy 2.5 V independently from

Vin (I try 230V and 110V) and Rload (I try 60, 50, 40, 30 ohm).

Any suggestions?

Hi,

There can be multiple reasons for the instability that you have reported. Some could be related to board layout and placement of components and others could be related to choice/selection of components.

We have a detailed application note for this product and I recommend that you review that carefully. I am providing a link below for your reference.

http://ac-dc.power.com/design-support/product-documents/application-notes/an-37-linkswitch-tn-design-guide/

Regards,

PI-Sarek

Hi,

I fix the instability. It was a poor ESR capacitor. The circuit seem to work well now but the voltage output is quite

lower than expected from your formula : 3.0 V instead of 3.6 V . I should fix it changing the R feedback value,

however this beaviour should conceal another problem. I have checked all components and all seem ok as

suggested on your application. The only difference with suggested schematics is the input stage: the suggested one

for design > 1W has impedence in return rail; my design require no impedence so, I remouve Din2.

Do you have any suggestions?

Are you designing a Buck Boost Converter?The Output Voltage is regulated based on the FB resistors value that you calculated for. You need Din2 Diode for AC halfwave rectification. Attached the Spreadsheet design for your specification, go through the spreadsheet ,Change the Input Capacitance to 6.8uF and RFB to 2.23K , please review it and let us know if you have any other questions.