over voltage output no load regulation

There is no DER136 in our reference design.

What is the correct DER number you are working with?

dear PI-Skywalker,

I am sorry for giving wrong der no actually it is DI-136 in LED-general category using TOP250YN all parts no as fig 2. In paper is mention as DER-136. p.l. find it as DI-136.

thanks & regards

amit patel

There is no DI-136 in the current reference designs.

It is recommended to use LinkSwitch-PH for the high power LED driver application.

Dear PI-Skywalker
I am attach documents of DI-136, and DER-136
I design for 24Volt 2Amp out put but output is goes
40volt at no load as we increase load up to 100mA outpu volts drop down at 12Volt, R14(470 ohms) too hot and become
black(not blown).this problem is occur with and without constant current
control loop. p.l. help me for this
thanks & regards

amit patel

Amit -


I figured out the confusion from earlier. DER-136 is in our archived reference design area.


Did you copy DER-136 exactly or have you made changes specific to your application?


On another note, while our TopSwitch products can be configured for CC operation for use with LEDs, the feedback circuitry can be somewhat complicated and the two feedback circuits (the CV section and CC section) can be tricky to configure so that they transition between the two regions correctly.


If your application is specifically for an LED driver, have you considered using our LinkSwitch-PH products? I've attached a very quick initial PI Expert design for a 24V 2A LED driver in the hopes that it proves helpful.

-The Traveler

thanks dear PI,
I exactly copy the der-136 with parts value as same in the refrence design,
thanks & regards

amit patel

amit -


Did you still need assistance with DER-136 or do you think you'll move on to our LED products (LinkSwitch-PH)?


If you can, I'd really recommend using LinkSwitch-PH for your LED power supply design. It's definitely possible to get TopSwitch to work as described in DER-136. However, at your power level, power factor starts becoming a problem (hence the negligible bulk cap in DER-136). When you throw in the complicated dual feedback loops...well...that was why we released LinkSwitch-PH!

-The Traveler

Dear PI
Thanks for recommend for link switch I am not able to open your attached file for 24 V 2A p.l. send me it in .PDF version I am using 32 bit PI software ver 8.5, In it LINK SWITCH PH is not available which software will support to it.
more over for our knowledge which factors are responsible for over voltage and poor load regulation in DER-136?

thanks & regards

amit patel

amit -


The zip file contains a file called "LinkPH LED Driver 24V 2A.pixls". This can be opened with PI XLS Designer which is part of our PI Expert Design software.


LinkSwitch-PH isn't currently supported in the graphical version of our design software but is supported in the spreadsheet design software I mentioned above. We're working on adding LinkSwitch-PH to the graphical version but it hasn't been released yet.


Regarding the copy of DER-136 you built, can you send me a PDF of your schematic, PCB layout and transformer diagram? I know that information is already present on our website but I'd like to compare them against each other. If you have any other design information (PI Expert files, etc) that you can post it would be helpful.


Also, if you have any other information, waveform images, etc, please let me know. I don't really have enough information from your original post to tell what the problem is.

-The Traveler

Dear PI

as describe above my circuit output is excess at no load 40 Volts instead of 24V at small load 100Ma is goes down to 28Volts, measuring parameters are as bellow

current at control pin is 7Ma at no load with load 6.89Ma, voltage across R16(200E) at no load is 13v with load is 0.9V voltage at bias winding after rectifying is 7.2V and it remains constant at any condition. I attach required PDF files I am not able to get wave forms in pdf format

thanks & regards

amit patel

Dear PI
I am designed a LED supply using DI-136 for 28V 1A, the out put voltage is goes high up to 40V as I increase load current 100mA voltage drop down to 25V. if i place a capacitor 3.3nF 1Kv across D7(FR305)I got 28V and good load regulation but top250 become hot.can I go for this practice? is it due to transformer primary leakage inductance? How can I measure leakage inductance? which factors are affected for leakage inductance? what functions of core cancellation winding and shielded winding in transformer? which performances effect without it? I attach schematic.

thanks & regards

Amit patel

amit Patel -


The added capacitance across D7 makes the FR305 (a fast recovery diode tr < 250 ns) and slows it down to make it function more like a standard recovery diode. This added capacitance appears in parallel with the primary interwinding capacitance and most likely increased the peak primary current spike during MOSFET turn-on (hard to check without waveforms though).


Clamp circuitry design and transformer design can require some trial and error. Sometimes the use of fast recovery diodes can cause high-frequency ringing in the clamp circuitry. If this ringing is coupling to other noise sensitive parts of the design, it might explain why the added capacitance is improving your regulation.


My recommendations:
- I'll stress again that moving to one of our LED specific products would be the best solution.
- If you insist on using DER-236, I would experiment with adding some snubbers on your main output and bias winding output diodes. To do this most accurately, you'll need a plot of your secondary and bias winding leakage inductance vs. frequency. You should be able to get this kind of plot on an impedance analyzer.
- Once you know your secondary and bias leakage inductance, you can measure the ringing frequency that you see across D10/D11 and D9. Use this frequency to backtrack to the leakage inductance at that frequency. Choose a series resister for your RC snubber that is approximately equal to the impedance |Z| of the leakage inductance impedance at the ringing frequency you see. Use a capacitor in your RC snubber that is 2-3 times the diode junction capacitance.


If you need additional help with how to do this, please let me know.

-The Traveler

dear pi,

             thanks for your best cooperation i done design for 45V1A led. driver on the bases of der136 and success with your guidelines, a little problem raise with the making a new p.c.b. design is o/p voltage at no load is 49V and 46.5V at full load.when put probe of dvm to ground for measure voltage tho o/p volts drop up to 1 to 1.5V.

in original p.c.b. o/p voltage is 47.2V and 46.8V at full load. more over  i inter cahnge transformers and  TOP250YN IC but problem is continue in new one and original is works proper with any componants. p.l. guide me for it  

amit patel

Amit - 

The problems you're experiencing is one of the main reasons this Design Idea is in the Archived Designs area of our website.  This was one of our early attempts at putting together an LED driver using a power supply controller that was intended for CV operation, not CC.  

Yes it can be done, however the design and troubleshooting process can (and as you're experiencing) requires a lot of work.  Without the proper tools to measure things like transformer leakage inductance, control loop gain/phase, etc this project will be incredibly difficult.

In situations like this, our LinkSwitch-PH products should be your primary choice.  They have power factor correction built-in, the feedback circuitry is already optimized for CC mode control and you're going to get much better output current regulation with these parts than with DI-236.

-The Traveler

dear pi,

           thanks for replay, my transforme inductance is 800Microhanery and leakage inductane is 6.8micro hanery , confusion is that how can i measure or set control loop gain/phase what is the require perameter for that?

with this problem my driver PF=0.97  and THD<15%

thanks & regards 

amit patel

To analyze your power supply's control loop you need a gain/phase analyzer.  

I've attached a good article from Ridley Engineering on control loop measurement techniques that are specific to Power Integration ICs that use a current signal instead of a voltage signal for the feedback loop.

-The Traveler

Dear pi,

           Once again Thanks for your best cooperation, this time I have some basic Questions. Like how can we define band width for top switch?  which factor are affacts for it?  how can we set it which bend width perform best? second is ringing frequency which factors responsible to generate ringing frequency? how can we control it?. and last in P.C.B. if we place TOP SWITCH away from transformer( gorund, and vcc tracks becomes sloghtly long) will effect in performance of system?

thanks & regards 

amit patel

With TopSwitch devices, you want to target approxiamtely 1kHz for your control loop bandwidth.  Without an frequency response analyzer, gain/phase analyzer or other appropriate equipment, tuning your control loop is going to be nearly impossible.  If you don't have access to this equipment, put together your design using PI Expert and have it generate the control loop component values for you.  This should get you pretty close.  I stress again however, that you *NEED* to get a gain/phase analyzer and measure your control loop.  This needs to be done at different combinations of input voltage, load conditions as well as temperature.

If you're having trouble with ringing, it tells me that you might have problems with your output rectifier snubber, clamp circuitry or some other parasitics.  I would need to see your PCB layout to be of further assistance with this.

Regarding IC placement.  Keep the TopSwitch IC CLOSE to the transformer.  You want to minimize your drain trace inductance and loop area.  Placing it far away will cause a lot of problems.

-The Traveler

Dear PI

            Thanks,   I am attach P.C.B. layout   *.pdf file, if we make Drain trace fill with solder ( make Drain trace thick) can it help to improve performance?  

amit patel

Whatever you can do to minimize trace inductance will be helpful.  Ultimately, you're constrained by the dimensions of the PCB.  So, you'll have to make the best out of the layout area you have available.

-The Traveler

Dear PI

             Is my PCB layout correct?, how can I measure trace inductance?

thanks & regards 

amit patel

Your PCB layout is somewhat difficult to read due to how dense the layout is.

I do see some issues with your layout though....You have several traces routed across the safety barrier which is generally a big no-no.  This will probably make you fail safety certification.

A good reference design that we have to look at would be: http://www.powerint.com/sites/default/files/PDFFiles/der256.pdf

It has a similar PCB layout as the design you're working on.  I would suggest using this as a good starting point.

You can measure trace inductance with an LCR meter.

I know you are fairly committed to using DER-136 as the basis of your design but I would still *STRONGLY* urge you to switch to one of our products targeted specifically at LED lighting.  A couple of reference designs that you could easily leverage would be: http://www.powerint.com/sites/default/files/PDFFiles/rdr290.pdf and http://www.powerint.com/sites/default/files/PDFFiles/der286.pdf

-The Traveler

Dear pi

as your recomandation i design led driver using lnk409 with der286 but i face a problem driver starts for 2second and after it turn off more over in load it gives 60V and drop down graguelly, Current at Fb pin is 112 micro amp. here iattach schematic & pi spread sheet.

thabks & regards 

amit patel

Amit - 

It sounds like something with the the feedback circuitry isn't setup correctly.  To be of better (and faster) assistance though, please repost this forum question in the LED forum.  This will get you in direct contact with engineers that work specifically with our LED products.

Regards,

The Traveler