5V, 0.225mA design for LNK306PN not working
AC- Universal input
DC- 5V, 0.225mA
Designed the circuit using LNK306PN as per design guide for LinkSwitch-TN Family, but output is 1.3 V @ 230 VAC input...
Inductor-- 680uH, o/p capacitor-- 100 uF, i/p capacitor-- 2 x 6.8 uf/400 V, Rb= 2K, Rfb= 3.9K, Freewheel diode- MUR460. Rpl= 1.8K, Cbp= 100 nF.
What can be the reason?????
Comments
Please find the attached schematic... I changed the output inductor value as per PIXI designer spreadsheet but still output constantly fluctuates. For no load & light loads we are using resistor type inductor. Is it because feedback current is fluctuating above & below 49uA????
Please, help...
| Attachment | Size |
|---|---|
| LNK 306PN (81 KB) | 81 KB |
Please find the schematic
| Attachment | Size |
|---|---|
| LNK 306PN (81 KB) | 81 KB |
Hi,
After reviewing the schematic, we suppose there should be no problem at all operating LNK306. However in your schematic you are using LNK304 instead. Could you please verify if it is LNK306 or LNK304? The 49uA on the FB pin corrresponds to the ON/OFF control of the IC. It is synonimous to variable duty or frequency but instead the scheme is ON/OFF control which allows regulation of the main output voltage. Based on the issue, the output fluctuates. You may be experiencing auto restart. Could you please verify if the auto restart blanking time is 800ms? If it is then you entered a situation where there is no feedback for 50ms. If there is a captured waveform then it will be more useful/helpful. In addition you may want to check the reference design report in the link below which is close to your design. Thank you very much.
https://ac-dc.power.com/sites/default/files/PDFFiles/der231.pdf
In the schematic uploaded, i have used LNK306P not LNK304P. Now the problem I am facing is that the pre-load resistor or or bleeder resistor R4 of 1.8K heats up heavily. I am using variac to control the AC input voltage . As I am increasing the AC input the output rises upto 40V so that I have to limit my AC input. And the pre-load resistor heats up badly...
What can be the reason??
Hi Abhishek,
Normally the pre-load resistor heats up when the current flowing through it is too high. Since your output is 12V then at 1.8k pre load resistor you should only have a current flowing of around 6mA. This is pretty small to heat up your pre load resistor. By the way what is the wattage rating of your pre load resistor? Now you've also mentioned that the output rises to 40V when you are inputting AC. This means that you do have some possible problem with closing the loop. Kindly check the FB pin if you are measuring around 1.65V. Hope this helps.
Hi,
THank you very much for using Power Integrations product. Do you have a schematic file or capture of your circuit? We would like to verify and check it. Thank you very much.