UCC28950-Q1: Power-up test of high voltage converters

Hello,

Your inquiry is under review and I will get back to you shortly.

Regards,

Hello,

It sound like this is your first high voltage power supply you have worked on.

Is this a new design?

One thing that you need to be causes of is that power supply testing is dangerous and should only be handle by qualified and trained personal.  Lacking the proper skills when designing and testing a power supply can be hazards to your health.  If you have never designed a power supply you might consider working with a consultant on this design.

If regards to not blowing up a power supply it needs to be designed correctly.  Before even applying power I would double check your design to make sure it was done correctly and all the components are sized correctly.  The following link will bring you to an application note that goes through the step by step design process of phase shifted full bridge (PSFB) using the UCC28950.  Within this application note is a link to an excel design tool goes along with it.  It calculates the maximum peak current, rms currents and maximum voltage ratings of all the components used in the PSFB design.  I would recommend sizing these electrical components for 125 to 150% of the maximum rating the design will be exposed to during normal operation.  

https://www.ti.com/lit/pdf/slua560

Before evaluating a new design it may be in your best interest to evaluate a design that you know is working.  The following link bring you to an a users guide for a 600 W phase shifted full bridge converter evaluation module (EVM).  You might want to order one of these and evaluate it before testing your new design.

https://www.ti.com/tool/UCC27714EVM-551

A word of caution, when evaluating a power supply make sure all safety precautions are taken.  You need to receive this training by qualified personal and is too vast to list in this e2e post.

The power supply being evaluated needs to be isolated from Earth Ground and should never be probed actively when the power is on.

Some companies recommend testing the design an a insulated box from safety to protect engineers from harm.

I generally start by:

1. Double check the design components and layout.

2. Power the PWM controller and evaluate it with no input voltage and output voltage.  Just to make sure the control loop is function and the gate drivers are doing what I expect them too.

3. Find a reliable DC supply where you can limit the current.  Start by limiting to 15% of the specified output.  Load the output with a 10% resistive load rated for the correct power level.

4:  With the limited power supply, you could bring the input voltage to 50 V first just to check to make sure everything works as you expect.

5.  Once you believe everything is O.K. at the lower voltages you could bring it up to the minimum input voltage the converter was designed for.  In most cases this is less than 5 to 1 on the input.

6. Please do not probe live circuits.  Connect the probes with no input power and capacitors discharged.  You should monitor high voltage capacitors with a volt meter to make sure they are discharged before handling any circuitry.

7. Start by evaluating critical test points such as CS, error amplifier output, SS, voltages across the transformer, switch nodes etc...

8. Once you have debugged the design and convince it works at 10% load you can gradually increase the output load and evaluate the critical designs critical nodes; as well as, the devices thermal characteristics.  I would go in 5% load steps just ensure everything is O.K.

        > Please note before doing this test you should increase the DC input supplies current limit to handle the appropriate power.

9.  Once you are convinced the design is functioning correctly, you will want to check the design for robustness.  That would be such things as startup and load transient testing.  Still why doing this you need to evaluate the design to make sure none of the absolute maximum ratings are exceeded.

10.  Once your a satisfied with your design it is recommended that you test it for reliability and production.

11.  Please note that these are just general recommendations and do not replace safety training by a professional.

I found this application not that will give you guidance on how to debug a power supply that you may find useful.

https://www.ti.com/lit/an/slyt638/slyt638.pdf

Regards,