RDR 290 75W design issue

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i have used your PI RDR 290 75W design and i am getting some of the issues
that is


1. No Output Votage Even when IC LNK420 BP pin is getting 5.98V & across the cathode pin of D7

2. Drawing more current and also low cureent at the output.

3. how to reduce the THDl ess than 10% in this design ( I have used  a capacitor of 10nF/1Kv in
    series two resistor of 1.5ME/1W(1% Tolerance) in between R5 and VR1  and
    is connected to FB pin of IC LNK420 



1. What is the LED voltage you are loading right now? Please make sure that you are operating within the operating LED load voltage of the design.  Else it will hit overvoltage protection.

2. Make sure that the unit is functioning before you add an RC feed to FB pin.

3. You can give a try on adding RC feed (Anode of D1 to FB pin) on the FB pin to improve THD. Make sure the rework is far from noisy path.

Can you send us a drain voltage waveform when the unit is not turning on.   10ms/div and  100us/div time scale. Vin? LED type and connection.





               1. I am using the output 29V,2.1A  LED Load.

               2. LED Type -- Philips LumiLeds Rebel which is Vf=3v, Curent of each led is Drawing 700mA

               3. I do not have facility of checking the waveform


 And another issue i have faced is that the unit is turning on at 75VAC and it is turning off at 100VAC where i have checked the BP pin Voltage it is 5.98V when it is triggered on and in off condition it is giving 2V and also V Pin is getting voltage 


The load is not clamping at a desired output voltage.  An actual LED load will have a rising voltage as the LED dirve current is increased.

At 70Vac, the output curent is not at full drive that is why you have the output.  Try to reduce the number of LED at higher input voltage and observe.

By the way, I guess your unit is hitting OVP.  If you are curious for the actual volage of your load, you can disable the protection by removing D7.  Just be careful becuase if there is a problem in your load it might explode your unit. 

Or you can check the load by directly appying a DC supply, just limit the current to avoid breaking the LED load.

Please be specific on the part number of LED.  You need to make sure that the LED is rated above 3A to avoid breaking the die of your load.







                1.LXML-PWC2-TWOR this is the part no the philips led what i am using.

                2.i am getting o/p voltage 28.80v & o/p cureent 2.1A.

                3. i am using 1N5408 Diode(D3) instead UF5408 Diode thus it causes any issue to the unit.

                4.after 24hrs burn in test the unit is getting failed & if i change the D3 diode 1N5408 to Uf5408 it is working                              what may be the issue.

                5. what may be the issue for the auto shutdown mode in the unit.

                6. what is the exact OVP voltage of the design as i am getting cotoff at 285VAC and it is turning on at 250VAC                          but in  the spreadsheet it is given 325VAC Cutoff of he OVP. 

                7. and one the issue i faced is that after 250VAC the unit is turning off and it is switching on again what may be                       the issue.   


The Trr of 1N5408 is larger than UF5408 that cause the device to overheat.  As the diode temperature goes up, the trr also increases that cause U1 to hit thermal protection.

Please make sure also that you are using the recommended D9 and D10 becuase slow diode will cause high leading edge spike in the primary switch.

By the way, make sure you have a heatsink in U1. For this power level you need a heatsink.

The design was verified in a regualted AC source oup to 300Vac without any problem.  If you are using a variac directly connected to the noisy outlet, then there is a tendency to hit primary OVP.  It will be good if you can send us the AC input characteristic. Another cuase might be is if you are using a different D9 and D10.  Make sure you are not stressing a subtitute part.

By the way, measure the voltage across C3.  It should be related to the peak input voltage (Vac) you are applying.  This is to make sure the input line is not too noisy.





                         As i am getting output votage 28.80V and Output current 2.1A 



im getting out put voltage 30-45v but poor out put current plz help me


Hi Kishorekumar,

What do you mean poor output current?  Out of regulation or line regulaiton issue or line regulation issue?

Anyway if the output is too high or too low you can adjust R11.

If you want tighter regulation use LYTSwitch-4. https://led-driver.power.com/products/lytswitch-family/lytswitch-4/

Please read this document:https://led-driver.power.com/design-support/product-documents/application-notes/an-59-lytswitch-4-design-guide/




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