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Original question:

PMP7760: Zener Calculation

Wide Input - Output Is not coming out

VIVEK NIRMAL
Prodigy 200 points

Part Number: PMP7760

Hi Ti team,

This is my second thread on this forum as the first one which I've posted for PMP7760 transformer design calculation verification.

Now here, I made the circuit as per the PMP7760 with the GCI G094215LF and powered up with 200VDC but output is not coming out. I guess transformer is not switching at all.

so, To rectify the problem I measured all the voltages with help of multimeter and following are the observation which I have come across under no load condition.

  • Vin= 14Volt
  • Vcc =  4.1 V
  • UVLO = 3 Volt
  • RT = 2.3Volt @ 220 kohm to GND
  • SS = 2.5Volt
  • Out = 1.9Volt
  • CS = 1.83 Volt
  • FB = 1.2 Volt
  • Comp = 3 Volt
  • In shemetics D2 diode cathod has 14volt and anod has 0 volt
  • At Q3 BC547 base has 3.6 Volt.

From that, few conclusion I can make

  • I have come to know that VCC should be more than 5 Volt.
  • CS pin should have low while device is not switching.
  • i also note that VIN and UVLO are in a proper range, so the RT, SS and COMP voltages are normal.
  • FB divider voltage is correct for VIN pin voltage of 14

I am attaching you our inhouse developed schematics , and transformer detail with gerber view for your reference.

please suggest me some solution regarding this as we are stuck at this stage.

Eagerly waiting to hear it from you.

GCI new updated R4 30W transformer G094215LF r 4.pdfLUBI-VFD-R1-0-DC-DC-PCB-TOP.pdfLUBI-VFD-R1-0-DC-DC-PCB-BOT.pdf

LUBI-VFD-DC-DC-R1-0.pdf

  • 0
    TI__Mastermind 46905 points

    Hi VIVEK

    The layout is not good. i'm not sure if the IC is damaged when power up the circuit.

    could you try to remove the R20 firstly before powering up the IC and check the Vcc voltage is normal. please use new IC.

    BTW, the experts of this device are out of office until first week of 2021. I will try to help with power electronic knowledge. but i don't much detail about this device and your design.

  • 0 in reply to Jasper Li
    Prodigy 200 points

    Thanks for the quick reply,

    As per your suggestion, I checked the voltage at VCC, CS pin, and Output Pin of LM5022, and these are as follows.

    • VDC Supply = 200
    • Vin= 14.12 V
    • VCC= 4.1Volt
    • Output pin = 1.8 V (Removed R20 )
    • CS pin = 1.8 V (Removed R12 then now there is no connection on CS pin still is showing 1.8 V 

    I've come to know that the CS filter should be as near as possible to pin.

  • 0 in reply to VIVEK NIRMAL
    TI__Mastermind 46905 points

    Hi,

    VDC is the VBUS+, correct? what is the voltage at device's pin1?

    the device VCC voltage is not correct. it should be typical 7V.

    no only the CS filter, the trace of power loop should be short and strong. otherwise, the parasitic inductor could damage the power FET. and the EMI is bad.

  • 0 in reply to Jasper Li
    Prodigy 200 points

    As I mentioned earlier,

    VDC=VBUS+ Voltage is 200volt. Also on Pin one has Vin= 14Volt and VCC is showing 4.1Volt while 1uF capacitor connected.

    just read the previous Answer you will get an insight.

  • 0 in reply to VIVEK NIRMAL
    TI__Mastermind 46905 points

    Hi VIVEK,

    did you swap the IC to a new one? i'm afraid the current IC is damaged as the Vcc voltage is only 4.1V. 

  • 0 in reply to Jasper Li
    Prodigy 200 points

    Yes, I swap the IC as well But I guess it dint worked. Please guide me into that I am stuck in between. if it is possible then have a look at the Gerber and Schematics and transformer datasheet. you can also check the Reference Design provided by TI PMP7760 as well.

    Waiting for the response from your side and TI teams.

     

  • 0 in reply to VIVEK NIRMAL
    TI__Guru* 78240 points

    Hello,

    Your transformer primary winding polarity appears to be wrongly used. Please cross check PMP7760 transformer connections.  Pin 1 should be connected to the MOSFET drain and Pin 3 to the input rail.  Could you exchange pin 1 and pin 3 connection on your circuit? 

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 200 points

    thanks, Youhao Xi

    I tried according to your suggestion but it dint work as expected as from the output side nothing is coming up.

    I applied VDC= 31Volt and the following are the measurement I have taken,

    • Vin = 14 V
    • UVLO=1.3 V
    • VCC=1 V
    • CS= 0.8 V

    Does Input VDC=31 V is enough to start up the board or should I increase the Input DC voltage?

    I couldn't understand why VCC is not building up to the voltage up to 7 Volt. I already attached every necessary document like schematics, Gerber and etc. Please go through it and share your valuable feedback.

    Waiting for the response.

  • 0 in reply to VIVEK NIRMAL
    TI__Guru* 78240 points

    It seems VIN pin does not receive adequate voltage.  Your Q2 may be in shutdown mode.  Please check D4 Cathode voltage. You seem using a TVS rather than a Zener diode there.  Please try to use the same Zener diode like the one used in the PMP7760.

    Thanks,

    Youhao