LinkSwitch adapter design
Hi all,
i am a new user and I am designing an AC/DC adaptor with universal AC input and 12V,350mA output.
The choice is the LNK625 switcher and I have a couple of questions about it.
My application power is less than 5W (i.e. 4.2W), do you suggest me to avoid the clamping circuit? In the datasheet I read that clampless circuit is possbile for P<5W.
What about the EMI/EMC behaviour? Is the clamp circuit involved?
Another issue is the bias circuit for the bypass pin. How is the right choice for evaluating if the bias circuit is necessary or not?
Thank you in advance for your support.
Nicola
Comments
Cochrane,
thank you for the answer, I will provide RCD clamp in order to meet less problem during EMC test. My application will be a "Class II", so I will not have earth connection, I can not use Y capacitor.
About the bias: the adapter I am designing will be part of a system and it will not work without load. The max power consumption of the circuit placed after the adapter will be 700mW but in normal operation the power will be about 250mW. During normal operation the average current consumption @12V will be 21mA. Since the small value, have I to consider this value a "no load" condition?
Thank you,
Nicola
When I say no load, it means 0 A in the output.For your application, I do not think the external bias is important, since you do not care about the thermal issue and the no load input power loss.
regards
Ok, thanks a lot for the information. I will come back if I will have other issues.
Regards.
Nicola
Hi Cochrane,
I defined the schematic and the layout for my application. Please, could you tell me if I can send to you or to a FAE the layout for a check?
Thank you in advance,
Nicola
If possible, PLS work with our FAE.
Regards
PLS check the answers of your questions:
1.the clampless design is possible since output power is less than 5W.
2. Without RCD clamp, you save some cost, but the EMC performance and voltage stress of the part will be worse. it is very possible that EMI can pass without RCD snubber, and you have to spend more time and effort for EMI for sure. Normally Y cap and RCD snubber can reduce the EMI significantly.
3. Bias circuit or not is mostly up to your no load input power requirment. If your requirement is very hard, (for example,<30mW), you have to use the external bias circuit to power the lnk-switch. Without external bias crcuit, the thermal of th part is worse too, especially at high line.
Regards