no startup

Please re-attach the files as I don't see them on your post. I can only guess at this point on why it might happen. If you based the design on RD-290, then please verify that the OVP circuit is designed properly. If not, it may cause the unit to latch. You may try to remove the OVP circuit and check if the unit can now startup normally.

At No Load, it is not unusual for the output voltage to shoot up since LNK-PH is not a CV controller. The OVP circuit is implemented to protect the driver from No Load condition.

Dear PI Crumb

 thanks for your valuable replay, here i attached my schematic, transformer, and pi expert sheet

regards 

amit patel

Please correct Q2 orientation.

Dear PI

   Thanks for replay, After correction(remove ovp circuit) I got 54V at no load and 38V at load but current is 1mA more over I observe voltage is not appear(0V) and current is 26microA  on FB pin. other parameters of all pins of IC is remains as datasheet, Now should i do for above problem. I am useing 27Kohms instade of 24.9Kohms resistor(for nondimmable) at R pin. 

regards,  

amit patel

Please re-connect the OVP circuit but you need to correct Q2 connection (the collector and emitter connection needs to be swapped, check RD290 for correct orientation).

What is your concern about No Load? Is it about the unit not latching? Please clarify what your problem is.

Dear PI

    Thanks for your replay,

     I reconnect ovp circuit and debug it as swapping Q2 now it is work, and gives output voltage 45V , and 0.79A, at this perameter Ifb is 195 microamp, now i want to increase o/p current up to 1.1A what should I do to increase o/p current?

thanks & regards

amit patel

Hi Amit,

I think the problem in your design could be

R5 + R6 = 3.909M

Rv2 = 1.402M (missing)

C5   = No use

R9 = must to be delete

Collector Emitter of Q2 interchanges

Please recheck with PI Engineer 

Ravik

Keep C5 (to set full mode operation) and R9 (it's the pre-load for the bias supply and it helps reset the device faster during short-circuit condition). Setting R5 and R6 = 3.909M and using RV2 = 1.402M usually result is better line regulation but I don't think it's what causing the output current to be different from the spreadsheet. You may try to implement this though to see any improvement. Q2 connection needs to be corrected as previously mentioned. Please measure the actual IFB by measuring the actual bias voltage. [IFB = (Vbias-2.3V)/Rfb]. Adjust the feedback resistor accordingly. You may also use PIXLS spreadsheet to fine tune your design.

Dear Sir,

The start pin number of primary winding is ok?

I think it must be pin 3 please correct me if I am wrong.

Ravik

In the schematic, the primary winding orientation is indeed wrong. However, the transformer specification has the correct winding orientation that's why I did not point out the error in the schematic.

Dear sir,

Thanks for your valuable guidiance,

As your guidance I rectify all wrong connections (transformer as well as Q2, Rv2) and make it ok but problem is still there, mroe over I talk to our local PI adviser the LNK409EG/LNK419EG  will not gives sufficient output power as my requirement whichi is 52W ( 48V and 1.1A)  I have to go for higher capacity of device is LNK420EG but this device is not available at indian destributor, or if I operate device at it's maximum capacity (ifb=210microamp) can it make problem? 

here I attach rectified schematic

thanks & regards 

amit patel

IFB=210uA is too close to IFB skip cycle threshold. Try to maintain it below 200uA. However, please re-check your design against the spreadsheet. You should be able to get 1.1A with IFB <200 uA. 

Try to increase bias capacitor to 22uF for lower ripple going to FB pin.

What is the actual bias voltage? 

In the latest schematic you sent, R5 + R6 should be 3.909M since you put RV2 = 1.4Meg.