Design of a PS for a train display supply, 5V, 80W with the following voltage range input: nominal inpu130V DC +-30% = 77-143VDC

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I have created a PS design in PI expert online using the Flyback CV/CC LED Driver IC with Integrated High-Voltage Switch and FluxLink Feedback, IC type number LYT6070C, see the attached file.

Input voltage is 130V DC nominal with a tolerance of +-30% which results in a range of 77 - 143V DC

Output voltage is 5V DC with a tolerance of 3%, power is 80W equals 16A

In the PI expert online simulation I cannot increase the output current more than 12A = 60W. I would need 16A to reach the maximum of 80W

The SW is asking for bigger output capacitor C11. I have change from 3 pieces 680µF to 6 pieces 820µF but it was only possible to increase the current from 10A to 12A not higher.

Is this not possible because I have reached the power limits for this input voltage, of the IC LYT6070C or are there other possibilities to increase the power?

Best Regards

Peter Michel

PIReport.pdf577.95 KB

I have managed to increase the current to 13A, but if I select 14A the following error message pops up, see attachment

20200512_061618106_iOS.jpg6.79 MB

Dear Peter.

Thank you for reaching out to us.
Your desing input and out spec are rather challenging given the relavely low input voltage and rather high output current required. This combination may lead the power supply to operate in deep CCM (Continues current mode operation) and in case if the Device Current limit is not enough, KP may drop below 0.1, hence the error message you are experiencing.
Just as a clarification, PI Expert only allows you to specify a maximum output current of 15A for LY6 product family.

I noticed in your report that you are using LT6079 which is not the hihgest current limit device.
Try swithing to LTY6070 with Increased current limit. if you are still getting the error message, increase your VOR to around 120V. you should then be able to input 15A output current. Once you have entered the new output current, double chck your device size as in some instances PI Expert reselects the device based on the total output power.
At this point, now that you were able to enter the high current output spec, I would strongly racomend to optimize your desing by means of the inbuild optimization.
You can optimize your desing by clicking either on the target icon (also called Optimize button) or on the icon which resembles a magic wand (also called Auto design button). The difference between the two buttons is that the first one optimizes your desing while retaining the frozen parameters and components, the latter discards the user selections and optimizes the desing with no restrictions.

if you click on Auto desing PI Expert will be reselcting the output capacitors and device size. In order to avoid that you could follow these steps.
1) if you have frozen either FS or VOR go to Key Parameters functional dialog, on the left side of the screen, and unfreeze them. Most likely the desing will worries though.
2) Now Click on the Optimize button (the target icon). PI Expert will optimize your desing keeping the selected Device. LTY6070 and the selected output cap Configuration

I have created a simial desing to your spec for you to have a look. here is the share link.

Hope this helps.
Best regards
PI-Star Lord

Dear PI-Star Lord,

There are still two open issues from our side for the design with this concept.

Is it possible that the power supply works with the input voltage of 77V DC?

Is the output current limited to 15A at 5V in the simulation SW only or is that also valid for the actual circuit? We need 16A at 5V. Will the real circuit be limited at 15A?

Mit freundlichen Grüßen / Best Regards

Peter Michel

Dear Peter.

Answering your first question, If PIExpert or PIXLS do not flag any warnings or errors using 77V as DC input voltage, then, there should not be problems for your power supply to work correctly. Of course, since PI Expert is a math based design tool, you can expect your bench data to differ slightly from what the tool displays. For this reason, it is always strongly recommended to validate the correct operation of the power supply on the bench.

Now, coming to your second question, the controller won/t limit the output current at 15A. Like every software, PI Expert has operational boundaries; these boundaries are based upon the vast majority of real applications. Of course, it goes without saying that if your desing is based on a 15A output current specification and your application draws 16A you can expect the power supply not to work as expected. This brings me to the next point.

If you want to design your 16A output current application, you can use PIXLS rather than PIExpert. PIXLS is less sophisticated in terms of user interface, does not provide loss calculation and does not automatically optimize your design. On the other end though, it does not impose any limits to the designer in terms of output voltage and current.
You can select PIXLS designer on the product portfolio page. When you select LYT Switch6 – DCDC Flyback, click on the button PI XLs rather than PI Expert on the right side of the window.

Please, do not hesitate to contact us if you needed to.
Best regards
PI-Star Lord