# LNK420EG RDR290

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I designed led driver with rdr290. When it connected connected with 36v 90w led it gives 37v 2.17A ,ie nearly 80W.
1.Is it work in cc mode with 24v 75w, 36v 75w, 48v 75w led lights???? If no, is there any method to implement it???
2.When i connected with 54v 25w led i got 52v .5A .is it work in cc mode???

Hi,
RDR-290 is designed as CC-mode. A properly designed LNK-PH solution can work from 24V to 48V. These are the tricks to do it
Design the Vout at 36V such as the (Current from the bias winding)IFB = 150uA; This will give you some room for load regulation such that at 48V IFB =200uA and at 24V IFB= 100uA. Note that Load regulation is controlled in the bias voltage. Please make sure that good magnetic coupling between bias and output winding.

Please make sure that the duty cycle is not limited to deliver the minimum and maximum Vout. Refer to the datasheet for the limits.

Regards,
PI-Jono

Hi Jono ,
Thanks for your reply. The device now works without R20.With R20 it just blinks and off.Why it not work with R20?

Is there any method to control the output power,such as by using pot ?
With Regards
Raneesh E

Hi Raneesh,
Congratulations, your board is working! R20 is link to OVP circuit. It only means your peak output voltage is hitting the reflected peak voltage in the bias winding. You need to optimize the turns ratio of the bias to avoid OVP.

Since your application is non-dimming, you can set the Vbias at 12V at Vout minimum. Then set your OVP at Vout max X 1.1.

Please note that R6 and R7 are for line compensation. VR3 and R20 is for OVP. R11 is for Iout.

The basic concept is as the Vout is increased, current through R11 is also increased proportionally (Vbias is reflected voltage of Vout). Thereby, it will increase its power and maintaining the output current.

I hope you can optimize it and meet your spec. You are almost there....

Regards,
PI-Jono

In board if I emove R20 it works with 40v and 2.1 A but after placing the R20 the current is zero and goes upto 15v and then decreasing.Then VR3 is removed same condition is observed no current and voltage is 15V but when I remove the Q2 It gives 42V and 2.1A currrent and at VR3 negative end 29.3V is there and other end 6.3V is there what I can do in this ckt to run at 32V and 2.1A.

hi,

If you already remove VR3 and the unit still does not operate normally, then you have an issue with Q1 or Q2 turning ON due to leakage current. You can try adding a pull-down resistor across C12 or increase R13 and R14 to reduce the base current. Basically, you don't want the leakage current to falsely turn-on Q1 or Q2.

Thank you

PI-Crumb, My design is working ok 2.1A current is achieved with 36V Led Load. Can this RDR-290 work upto 24-48V Led Load with 2.1A  CC  regulation?

hi. The IFB is the key here which has a usable range between 85uA to 210uA. Theoretically, your design can work from 24V-48V.

My suggestion is for you to design at 48V, 2.1A and set IFB to around 200 uA. You might need to increase the value of the upper Vpin resistor RV in order to deliver the power. Honestly, your power requirement is beyond the recommended power rating of the device. Heavy heatsink is necessary.

The bias voltage must be designed such that it is still above 12V at 24V output. I say target Vbias at least 36V at 48V output.

I got to warn you though that the CC regulation must be verified. You may need to relax the IOUT tolerance to be able to meet the 24V to 48V spec.

Hii.. I want to design reference for 1A CC design with 40 to 50 V DC output with LNK419.

https://piexpertonline.power.com/site/index

I have replaced Lnk by Lyt with ETD29 design 1.7A current 24-48V. It works properly with open enclosure. and After placing in close enclosure after 15minutes it shutdown. the current and voltage are in the range. 1.65A current adn Voltage 40.9V.  Please provide feedback for this problem.

In above said prototype, after 15 to 20 minutes circuit shutdown , remains 15 to 20 seconds off then again it starts and again it shutdown for 15 to 20 seconds what will be the issue??

Please provide feedback for this problem. Which protection fires can not undertand ?

Temp. of LYT4228 IC is 57 C .

I am using 42V Led Load.

Please provide the solution. I have developed PCBs and also purchased the BOM and LYT4 also in bulk.

The drop from 1.7A to 1.65A is about 3% and can be attributed to system temperature coefficient (TC). The LED voltage also drops with temperature.

For the shutdown problem, the IC never had 20s auto-restart timing. Can you attach your schematic?

The only thing that I can think of right now is whether the line OV is somehow getting triggered or the Over temperature protection kicks in although it's unlikely if the device temp is only 57C.

Disable the OVP circuit too just to isolate where it is coming from.

Thank You for Replay

Here I am attaching schematic , I have tried for line OV protection by attaching 5.6V zener between V pin and S pin. but same result is observed.

By removing R20 I will try to disable the OVP, but before that what steps to be taken care for any failority of components.

By opening R20 and VR3 OV protection is bypassed but same Issue is repeated.

Fine Tunning of V pin and FB pin is done. But still same problem is observed.

I request you to please give feedback for the solution . Schematic is attached in above comment.

Can you try replacing D4 with an ultra-fast diode? I noticed you are using a GP diode.

Also, the device temp of 57C seems very low for the power that you are operating at. I remember getting wrong measurement using a thermal camera if I measure at the heatsink because the reflection causes the infrared to measure incorrectly.

It is possible that the device is indeed going into OTP and requires a larger heatsink. But first, change D4 to ultra-fast.

Hi guys, I did a development with PIExpert 8 for an LED driver of 78V 800mA. I selected LNK420E and transformer with EER28. I made the printed circuit according to my needs and I carefully respected all the indications. In fact the prototype works very well except for two things:

A) Operation is DM instead of CC.

B) The snubber net heats too much.Specifically R5

The first one I suppose is corrected increasing the inductance but the second one requires more work.

Please see in attached schematic and oscilloscope images.

The yellow color corresponds to Vcc (rectified voltage input, transformer pin 1) and green to the Drain of the LNK420. With great courage removed R6, that is to say that I completely eliminated the mesh. I know, a very dangerous game. Incredibly everything works well and the transient opening, although reaches almost 800V. Congratulations to PI !.I can kill that transient easily with 1nF and I have enough time to download it with 200Kohm in parallel. They agree?

Then I do not understand why they keep circulating almost 10mA per R5 throughout the toff. That energy is lost uselessly and D1 makes it look directly as current over the LEDs.

Another question: what is the mathematical expression that links the voltage in pin V, the current in FB with the current or circuit activity cycle ?.

The last one: is it absolutely necessaryD3?

Thank you very much.

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Oscilogram 188.32 KB
Oscilogram 289.92 KB
Schematic180.88 KB

Hi guys, I did a development with PIExpert 8 for an LED driver of 78V 800mA. I selected LNK420E and transformer with EER28. I made the printed circuit according to my needs and I carefully respected all the indications. In fact the prototype works very well except for two things:

A) Operation is DM instead of CC.

B) The snubber net heats too much.Specifically R5

The first one I suppose is corrected increasing the inductance but the second one requires more work.

Please see in attached schematic and oscilloscope images.

The yellow color corresponds to Vcc (rectified voltage input, transformer pin 1) and green to the Drain of the LNK420. With great courage removed R6, that is to say that I completely eliminated the mesh. I know, a very dangerous game. Incredibly everything works well and the transient opening, although reaches almost 800V. Congratulations to PI !.I can kill that transient easily with 1nF and I have enough time to download it with 200Kohm in parallel. They agree?

Then I do not understand why they keep circulating almost 10mA per R5 throughout the toff. That energy is lost uselessly and D1 makes it look directly as current over the LEDs.

Another question: what is the mathematical expression that links the voltage in pin V, the current in FB with the current or circuit activity cycle ?.

The last one: is it absolutely necessaryD3?

Thank you very much.

TitleSize
Oscilogram 188.32 KB
Oscilogram 289.92 KB
Schematic180.88 KB

HI sir,

Iam using LNK420EG as per the Design follow the RDR290 application , Iam using same RDR290 gerber file getting good results in PF 0.976 and THD 12% .Iam facing the problem with changing the layout design ,In my smps getting power factor 0.86 and THD is 50% .

How to reduce the THD less then 10% and increse the power factor 0.99. Pl. help me.

Please check the switching waveform to make sure there is no transformer saturation. Please double check your components as well before concluding that it is due to the layout.