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UCC28633: My design for 13V 65W Power Supply using UCC28633 is not working

Part Number: UCC28633
Other Parts Discussed in Thread: UCC28600, PMP9208, PMP

Hello...

I have designed a power supply using UCC28633 and developed the board. My design was based on UCC28633 Excel Design Calculator and WEBENCH design tool. Unfortunately, when I assembled the board, the board behaves like dead. The DRV pulse comes at 1 Hz frequency. The transformer winding ratio Np:Naux:Ns is 47:6:6. The Core used here is ETD 19/16/10 with Al value of 122 nH/T2. Lpri is 270uH. The MOSFET we are using is STB13N60M2 which is similar to the MOSFET suggested in the application note. The Bias winding i.e. MAG gives me 1.8V. It seems we are missing something. Please look at the schematic attached herewith to help us solving the issue. The output voltage what we get is also like 1.8V. Everything here I have mentioned was in no load condition.

Regards,

Sambuddha13V 65W AUX.pdf

  • Hello,

    The 1 Hz switching frequency would indicate and over current, over voltage or input under voltage fault.  There is an application note that goes into detail on how to trouble shoot PSR flyback controllers that may help.  You can find it the following link. http://www.ti.com/lit/an/slua783/slua783.pdf

    The main issue that I have seen is that transformer aux winding ringing will trigger and OVP. The application note discusses how to resolve this with snubbers and recommends the transformer leakage inductance be set to less than 3% of the magnetizing inductance.

    There is an offline 85 to 265V ac to regulated 18V 65W evaluation module/reference design that would work for application.  It uses the UCC28600 quasi resonant controller with opto feedback that you could modify for your application.  You can find it the following link http://www.ti.com/lit/ug/sluu263c/sluu263c.pdf and you can order this from TI and modify it for your specific application.  You could probably get this to work just by adjusting R18 R17 resistor divider.

    Regards,

  • Hello Mike,

    Thanks for your reply. I have checked and confirmed that the Tx we developed meets all the design values including the leakage inductance within 3% of the magnetizing inductance. The entire circuit is exactly same as given in the application note of PMP9208. Even then, the IC does not start-up. There must be some FAULT that seems to be triggered every time I switch on. Therefore, I am thinking to start the IC UCC28633 seperately without the transformer and its winding.

    What I would like is to see is that the IC generating its DRV signals when it is powered externally and feedback given at its pins using external power supplies. The controller IC is pretty simple, have only 8 pins. Out of 8 pins, SD would be kept open and GND pin is connected to Ground. HV Pin will be connected to the AC side through the Diodes and 200k resistors. A 1uF 305V X-Cap will be connected across the AC supply. The Transformer and MOSFET will be taken out from the board. Planning to provide a DC voltage of 12 - 13 VDC Bias Winding terminal on my board. Therefore, VDD Pin gets that 13V bias voltage. Planning to provide another DC voltage of 200mV at the CS pin. VSENSE will receive the voltage as per the voltage divider network placed on the board. Would like to see if I can get the DRV signal. Is this possible, what do you think? If not, please tell me how to get this IC working separately without using the Transformer. If we are able to do this, the rest part would be easy.

    Regards,

    Sambuddha

  • Hello Sambuddha,

    I reviewed the PMP design and D6 C16 clamp/snubber does not look correct this might be what some of the problems you are having.  Increase C16 to 1 nF and put a 511 k ohm resistor in parallel with it.   Next add a resistor in series with the D6 to control the clamp voltage.  10 to 20 ohms should do it.

    The controller may be trying to startup.  I would suggest probing the CS, DRV, VDD and Aux winding and trigger on the DRV pin. 

    If the device is entering a fault it will give three gate drive pulses and UVLO cycle before starting up again.  With a long time base it will look like there is a saw tooth on the VDD pin.  You can then evaluate the aux winding and current sense signal to see what the fault is and correct it.

    The faults that can cause this are as follows.

    1. Input under voltage

    2. Output over voltage

    3. Over Current

    The number one reason for these style converters are noise on the aux winding triggering an OVP.  I did notice the PMP design you reference has a place holder for a snubber on the output rectifier.  If the modified clamp does not fix the issue and the converter is shutting down due to OVP  because of noise on the aux winding.  You can use this snubber to dampen the noise and hopefully resolve your issue.

    Regards,

  • Hello Mike,

    Thank you very much for your input. Sorry for my delayed response. The problem is sorted out as per your input. The controller was going in Over Current fault mode. The snubber and the value of Current Sense resistor had to be altered to achieve required O/P voltage and current. These are the following changes we made:

    1. The current sense value had to be adjusted to 140mOhm.

    2. As you suggested "Increase C16 to 1 nF and put a 511 k ohm resistor in parallel with it.   Next add a resistor in series with the D6 to control the clamp voltage.  10 to 20 ohms should do it." We have used 10nF @ C16 and a 511 k resistor in parallel to that. Furthermore, we have also added a 22Ohm, 5W ceramic resistor in series with the clamping diode.

    These changes solved the problem. We are able to achieve 13VDC at the O/P. We have checked the load regulation as well (within 5% of No Load O/P). The Output peak-peak ripple is also 23mV @ No Load. Thank you very much for your kind support.

    Regards,

    Sambuddha