PMP11612: No Output from isolation transformer

Anuraag Rajasekhar

Part Number: PMP11612

I prototyped the PMp11612 on a PCB, but the Isolation transformer (POL-05020) is not producing any output. The Schematic is attached below. Pins 1 and 2 of the transformer are getting around 170V, Pin3 has 0V and Pin4 is PGND. The output on Pin9 of the transformer is 0V when it should be 5V. Any idea what's going wrong?

Transformer Datasheet: http://www.premiermag.com/pdf/pol-05020.pdf

over 6 years ago

0 JohnFullilove over 6 years ago

TI__Expert 5120 points

Anuraag, thank you for your interest in Texas Instruments TI Designs. Your query has been received and has been forwarded to the design owners from our Power Design Services team. You should be receiving a response from the team there in a few business days. Again, thank you for your interest in Texas Instruments.

Best Regards
J. Fullilove
Manager, TI Designs

0 Yingyang Ou over 6 years ago

TI__Prodigy 605 points

Hi

Please check the value of R37. We cannot see the value clear in the schematic. But is should be not the value of 68k used in PMP11612. This pin is used to sample the input and output voltage. It is a critical branch for the whole system. The current value of R37 should be very small, it cannot scale the bias winding voltage effectively and the actual voltage applied to VS pin may be out of its spec when the input is applied at the first time. So, please also check whether the controller is failed after the R37 is corrected. If possible, please replace the controller with a new one. thanks!

0 Anuraag Rajasekhar over 6 years ago in reply to Yingyang Ou

Prodigy 80 points

So the resistor value should be 68k right? The resistor in current design is 68 which is my mistake.

0 Yingyang Ou over 6 years ago in reply to Anuraag Rajasekhar

TI__Prodigy 605 points

Yes, please use 68k res for R37. Please also replace a new controller. With 68Ohm, the VS may be broken.

0 Anuraag Rajasekhar over 6 years ago in reply to Yingyang Ou

Prodigy 80 points

Thanks a lot for your input! This was very helpful

0 Anuraag Rajasekhar over 6 years ago in reply to Yingyang Ou

Prodigy 80 points

I replaced the resistor with a 68k Ohm resistor and also replaced the Chip, but I'm getting the same results. I think it might be because of the MOSFET. I couldn't source the one used in the reference design, so I'm using https://www.mouser.com/new/stmicroelectronics/stmMDmeshII/. Would this be causing any problems? Also what should be the voltage readings at Pins 1.2 and 3 of the transformer?

0 Yingyang Ou over 6 years ago in reply to Anuraag Rajasekhar

TI__Prodigy 605 points

Hi,Anuraag,

Your FET should be OK. Before power up, please check the R30 (43K) and R3? (620K) are both OK since the previous fault may also destroy these two resistors. After that, please monitor the VCC voltgae using voltgae probe, generally, it should ramp up to >21V once the input is applied. Meanwhile, please also use a voltage probe to see the Pin 2 of transformer. There should a voltage train at this pin. The high level should be higher than input voltage with a ringing at the rising edge. And the low voltage should be very close to zero. Pin 1 should be the stable input voltage. Pin 3 also has a voltage train which is reversely with Pin 2, as well as different voltgae level (depends on the turn ratio of Pri:Aux). Please monitor these pins and check whether the chip works.

0 Anuraag Rajasekhar over 6 years ago in reply to Yingyang Ou

Prodigy 80 points

I don't have access to an oscilloscope right now, but I will get back to you on that. I was also not able to source the inductor used in the design, but I used RCR875DNP-221K as a replacement. Would that be causing any problems?

https://www.mouser.com/Search/ProductDetail.aspx?R=RCR875DNP-221Kvirtualkey56750000virtualkey851-RCR875DNP-221K

0 Yingyang Ou over 6 years ago in reply to Anuraag Rajasekhar

TI__Prodigy 605 points

Hi Anuraag

Your inductor would not make the system failed. It will impact the EMI performance.

Please try to get a oscilloscope since it is essential for a power supply design. The fact is that there may be something error on your board. So, we need to locate the root cause.

You can also try to contact your local TI sales to see whether they can apply a PMP11612 board from TI. Thanks!

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PMP11612: No Output from isolation transformer