LNK302 for AC/DC to 15mA ouptut
Dear PI team,
I am working on a high volume project, and my specification are to build an ultra low cost AC/DC with an ouptut at 3.3V @15mA .
Do you have a reference design for ultra low cost AC/DC with an ouptut at 3.3V @15mA max ? Or something very similar ?
And do you have as well an excel file which permits to calculate those ?
I am particularly interested to see what would be the recommended inductor and capacitor (value + voltage rating), as this seems to be the most expensive passive part driving the overall cost.
As for the input filter, i see in your app note that there is different choices , and for 0.25W and below, it is recommended to only use one capa of 2.2uF at 400V, while for higher current it is a PI filter with 2 of those capa + an inductor. It looks like it is a big price concern as well, as the 400V capa are expensive. Does it possible / recommanded to downsize the value of the inpiut capa to lower the price ?
Thanks,
Flo
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Thanks for your prompt answer !
Reference design looks good to me , that is close to what we are looking at . Only worried is that we cannot use electrolytic capa, which are the very cheap one. What would you recommend to use as reference as a substitution of the EKMG401ELL2R2MHB5D proposed in the BoM ?
Besides , for the inductor , do you have the formula to calculate it ? I would like to know if we can use lower values for this one .
Kind regards,
Florent
Hi Florent,
May I ask the reason why you cannot use electrolytic capacitor?
Regarding the output inductor, there are calculations on the application note of LinkSwitch-TN2 (page 23 - Appendix B) but those are also used in the PI Expert tool. Provided there also are the standard inductor values used depending on different parameters. You may check it on Figure 8 on page 11 as well as Table D.1 on page 28. Using a lower output inductor value introduces a warning in the PI XLs since it can lead to a shorter on-time of the MOSFET. That's why the reference design I provided used a typical inductance of 3300 uH which is also the recommended standard value.
AN-70: https://www.power.com/design-support/application-notes/an-70-linkswitch-tn2-design-guide
Regards,
Power Integrations Inc.
Hi Florent,
Regarding the alternative for the aluminum electrolytic capacitor, a possible replacement for it is the multilayer ceramic capacitor (MLCC). MLCCs offer several advantages, including space reduction due it its smaller size and lower profile, reduced ripple voltage due to their low ESR, and improved reliability due to the reduce self-heating. However, the low ESR as an advantage of MLCCs can also introduced risks such as abnormal oscillation or anti-resonance in certain circuits. To prevent abnormal oscillation, phase compensation can be implemented. Additionally, MLCCs with high dielectric constant (Class 2) are susceptible to capacitance variation under DC bias (DC voltage applied), which must be carefully considered during design.
Best regards,
Power Integrations Inc.
Hi Florent,
Good day and thank you for choosing Power Integrations.
Here is a reference design closest to the specifications you need (5V, 0.35 mA). You may check the link below:
DER-507: https://www.power.com/sites/default/files/documents/der-507.pdf
Regarding the input capacitor, the 2.2 uF is just a recommendation for the design. You may use a capacitor lower than 2.2 uF since you also have a much lower output power. However, by doing this, you still need to monitor your power supply for any unusual behavior.
For the calculation of the input capacitance, we used the table attached. But since you need a very little power, the calculation would give you a small value. You will only need one input capacitor for your design, but if you still want to downsize the value you may try to do so.
For the voltage rating of the capacitor, we usually just convert the maximum input AC voltage to its equivalent peak voltage. Hence, for a universal input, 265 VAC * 1.414 = 374.7665 V which is approximately 400 V.
I hope this information helps. Please let me know if you have questions and need further clarifications.
Thank you and have a great day ahead.
Best regards,
Power Integrations Inc.