Hi,

LNK-PH has input undervoltage protection and it was modified and improved in LYTSwitch-4 family.  The minimum pop-on angle of a rated dimmer (120Vac) like Lutron is able to operate at this level.  Try replacing the device using LYTSwitch4314 and verify in dimming if the performance is improved.  You can reduce also the size of the TRF because it is operating at 132kHz.   Temporary use your existing TRF for the testing.

By the way,in my test Lutron(600-PH-WH) will not turn on even using a 75W bulb load at minimum angle. It will not even emmit a light at 115Vac at minimum angle.  Please make sure that the TRIAC can trun-on at a minimum angle before troubleshooting the unit.  Make sure also that the TRIAC is operated at right line frequency (60Hz).  The internal timing of the TRIAC will be affected if it used in wrong line frequency.

Like the bulb, as you decrease the input voltage the light diminissed.  The LNKPH and LYTSwith-4 will have the same characteristic.

If you want a close loop that is proportional to the dimming angle and non-isolated then the right solution is the LNK-PL.  This device is adapative to line frequency and conduction angle of the triac threfore the output current is well controlled.

We highly appreciate your feedback and we are now deeply looking for the simple solution to address your concern.

Dear Jono,

                 Thanks for a detailed reply. We have taken UL approval for our 3 dimmable models with Link switch PH devices. So we cannot switch to LYT switches easily. Can you suggest a solution for Link Switch PH?

We tried changing RV resistor 4Mohms to 3Mohms and the dimmer is working fine upto 113V(we need the dimmer should work atleast 100v minimum). But output current reduced to 600mA from 700mA. Is it the right way to solve the issue by changing the RV resistor? How can we catch the lowered current?

Please note the  input is  90 - 132V .

Hi,

If you lower down the resistor for RV then you need to compensate it by decreasing the resistance for RFB.  The limit in decreasing the RFB is dictated by IFB auto-restart.

Looks like you can address it also by supplying the V pin during dimming.  Please refer to the attached doc for your reference; highlighted in red. 

Regards,

PI-Jono

Hi Jono,

             Thanks for your guidance. By decreasing the RFB, IFB limit is crossing(210uA). Can I go to LNK409 instead of 407 so that we will get a IFB of 175uA? Also can you explain the second method using attachment in your reply?

Hi Stalin,

The suggested circuit  will blank the undervoltage detection of the LNK-PH.  During dimming and at minimum input voltage the threshold for undervoltage is triggered (this threshold is not in LYTSwitch). This method will provide the minimum current of 30uA approximate that will blank the undervolage (page 14 of LNK-PH datasheet).

Please try the circuit, it will require one additional diode only.

You have a good idea, I never thought that.  Yes you can use LNK409, it will give you a better efficiency, just check the possible saturation during start-up.  You might need to readjust your transformer to avoid this scenario.

Regards,

PI-Jono

Hi Jono,             we tried the  circuit  to blank the UV detection in LNK-PH device.But there is no improvement in restarting at dimmer minimum. So I arranged LYT 4313 and we replaced the IC. Also  changed the Bypass pin capacitor to 100uF. Circuit is working fine with our existing RM10 Transformer. Now driver restarts at 105v at dimmer minimum with Skylark dimmer. But the transformer design sheet shows CMA value 3797. What will happen if CMA is more than 600?

Hi,

Nice, you have a significant improvement.  It is improactical to have a CMA above 600  because the copper size is too big(cost) for the application.  But in some cases it is okay to have greater than 600 in order to have lesser copper lossses and in order to have a better EMI performance.

You can try a layer of 1 in the primary winding in order to cost reduce your transofrmer design.

Regards....