LNK306GN

Hi


With your feedback resistors (13k and 2.2k) you really should not be seeing 25V on the output. The voltage should be around 12V.


The zener should also not be necessary, and in order to find your issue I recommend removing it. Have you followed the layout recommendations of the application note? Also, be sure to check the saturation current of the inductor. For your initial tests you may want to use an ultrafast diode for both the freewheeling and feedback loops.

Hi, thanks for your answer

Actually i don't know exactly inductor's saturation current. But when i bougth them, i asked 680uH-400mA and the guy give me the product. But as i said, not so sure. Do you really belive its because of inductors current?

I read layout recommandations. And changed my layout after that. I get 25V and its increase to 50V. After that i shutdown the system

Do you have any example similar my schematics? If you have please share with me.

Regards.

Under which load conditions and input voltage does this happen?


Do you have the 2.2kOhm resistor connected on the output side? (under no load conditions, this would be a reason for the output voltage to increase that much)


I don't have an example for your exact specs, but I do have a couple of examples:


Example LNK306 Buck boost


Example LNK305 Buck


Example LNK304 Buck

hi

finally i can get the value that i want. i changed the inductors and it works.

i checked the examples you send me. in the first one (Example LNK306 Buck boost)

and there is a rf2 connection i don't understand. can u tell me what is that and why did they use there? also its not shown on schematics? its look like just a cable or shunt. but i donnt understand what it is? do u know that?

Hi


I'm glad it's working. I am pretty sure that RF2 was something that the designer placed on the layout in order to get some extra flexibility when designing the EMI filter. This was not used in the final board (the connection was short-circuited).

So you say its not so neccesary. But i found some projects with LNK306 and they used the same wire. I thought it was shunt or fusible resistor or something. But i am not so sure to add that component??

And i want to ask one more question. In my project i need to use AnalogGroung(AGND) and DigitalGround(DGND) together. But with this shcematichs i have just one ground (RTN, and i dont know whats that meaning). Do u advise to use RTN for both ground??

You only need one fuse, and that is RF1 (equivalent to your R1 on your schematic assuming that R1 is a fusible resistor). So RF2 is not necessary.


This specific example I was showing you is typically used to turn on triacs for example. That is why there is a half wave rectifier, and the RTN is connected to neutral. If you don't need a signal referenced to AC, then you shouldn't use this type of half wave rectifier (usually harder on EMI). You can use a full wave rectifier, that theoretically allows you to have smaller bulk capacitors. More detail on this are in the app note.


I don't know your project, but if AGND and DGND should have the same reference and both are supplied by the LNK-TN then by all means connect them both to J1-2 on your schematic (equivalent to the RTN on the example layout).

Well I understand now. But still wonder something. I have two more questions if you interest.

First of it, what is meaning of RTN? :) (I know its something like GND but dont know to spell it)

Second is, i dont know the resistor i will use is fusible or not. I am not so sure of that. Maybe i wont use fusible for RF1, and than i need RF2 jumper. What do you think about that?

RTN stands for return.


As for your second question, you will (usually) need some kind of fuse in your circuit. A fusible resistor has the advantage of also limiting inrush current during turn on of the psu and it will also help (if only slightly) in EMI.
Fusible resistors also have limitations though, as most won't withstand more than 1kV differential surge.

Hi its been a long time not to answer. My project is working. I tried to get 400mA so used Coilcraft RFB1010-152 as in AN37 says. When i tried with power led its OK but couldnt works on Winstar 16x02 LCD & PIC16f877. So what can I do do u have advise?

Hi


I don't know the characteristic of your loads. You may want to try to put a capacitor in parallel with R3 (check image on your first post). If your load is requesting full power instantaneously this capacitor will help (as detailed on Figure 3 of Application Note 37).

OK I will try your advise. But what u suggest to select capacitor value ?

by the way, I used voltage regulator out of the circuit. I put lm7805 for 5V. With voltmeter I see 5V output. But after connect to load out of the circuit, voltage drops 3V. And circuit normally not works :S

Between 1uF and 10uF as specified on AN37

Hi,

I want to get 3.3v and 5v directly from 230v with less number of components and minimum size.

I have attached image files for the same. can you please share me your feedback on it , any improvements , reduction/removal of part, addition/change in part etc ?? Also I want to make PCB with less height and less spaced parts , but as you can see in image L1, L2 and C25, C26 are through hole parts and with almost 13mm height. Is there any replacement for this?? Also one issue is that as inductor are through hole and have small lead length so i cant bend them so any replacement for them also beneficial to me. Till now circuit works ok but now the space and height are major concerns so please help me out.

thanks

Hi Irfan,

I think this is the same question I replied to below. Thank you.

https://ac-dc.power.com/forum/low-power-design/2017/knowledge-and-support-required/