PMP41009: Which are the correct waveforms for the HV and VDD pins

Hi Shilin,

Could you share the schematic and the transformer spec with me? What's the input voltage, output voltage and current?

Best Regards

Linda

Sure,The schematic shows in backup_V1.0.pdf.

backup_V1.0.pdf

The spec of transformer  are as follows

IN figure 1 the input volt is 50V, In fiugre 2 the input volt is 350V. 

It's weird that I can't detect the output of the DRV pin。

In my opinion, as long as the VDD voltage reaches 21V, the DRV pin will have three pulses to detect UVLO, OCP, and OVP faults. If the faults exists, VDD will be pulled down to the shutdown threshold and recharged again. If the fault does not exist the circuit will operate normally.

Am I right?

Yes, please connect HV pin to HV_800 directly,  and change Rs1 to 135 kOhm, change Rs2 to 47 kOhm. Then try to power up the board with input 400V.

Sorry for the late reply. I used a new board and modified it as you said. The  waveform is shown in the figure where CH1 is the voltage of the HV, CH2 is the voltage of the VDD, and CH3 is the output of the DRV.

I added CH4 to measure the output voltage, the waveform is shown in the figure.The output is stopped when the output voltage reaches the calculated OVP voltage.

You can try to change C314 to be same with PMP41009.

Do you mean change C314 to 242nF? And  why is there a 750Ω resistor?

Keep the C314 as 470pF I tested the waveforms of DRV, FB, TP318 and TP320 as shown in CH1~4 in the figure, respectively.

When add R331 with 1kΩ，The waveforms become like this.

For this I have some questions

1. Is it because of an overvoltage fault that causes the chip to stop output? 

2. Which is the better waveform about FB?（Should I change the value of R331 or remove it?）

3. Is the voltage spike in FB too large(2V/div in figure)? I'm worried that it will damage UCC28740-Q1.

4. When the optocoupler secondary side is fully on, the voltage divider of the FB pin should be less than 3V, and why there is a voltage spikes up to a dozen volts.

5. How can I improve this circuit?

Thank you very much!!!!!!!!

You can try to change C314 to 220nF firsty.

In the morning, I changed RFB3 (R324) to 240k, and the circuit was working correctly. The waveform is shown in Figure 1.（The voltage spike of the FB is caused by the proximity of the probe to the transformer when measuring）

Now under this condition, I changed C314 to 220nF as you said, and the waveform is shown in Figure 2.

And I found that when I changed this capacitor value, the waveform of CS became better.

before：CH5

after:CH3

Can you tell me how this capacitor works?Thank you！

And what should the desired waveform from FB look like？

Ok，thank you.

G0t it，Thanks

The primary current is too large to damage the board. So how should I calculate the current on the primary side of the transformer for PMP41009, and how can I limit the amount of primary current? Thank you.

Both faults occurred on the CS resistor, and I think the primary current exceeded the capacity of the CS resistor. But I didn't connect the load when I powered on, only a 4.7k dummy load, why is there such a large current that makes the CS resistor explode.

Thank you

Pout =2*3=6W,Vout = 15V.Nps=8:1;

I want to know that how can i choose the IDS_MAX of MOSFET and the power of the Rcs？

Would you like  to tell me how to calculate it？

Thanks！

You can download the Power stage designer tool to calculate the primary RMS current, then you can calculate the Rcs power dissipated.

https://www.ti.com/tool/POWERSTAGE-DESIGNER?keyMatch=POWER%20STAGE%20DESIGNER

Calculate the primary peak current using the equation, you should ensure the transformer isn't saturation at this peak current.

Vcst(max) is 0.773V

Sorry I can't install apps on my work computer privately. So I probably won't be able to use the designer tools.

Is there a formula for calculating the primary current that tells me what its value is related to?

Thank you

And I still have an question that how UCC28740-Q1 determine the pulse width of the initial three pulses? If the RCS is shorted, will the first pulse width reach the maximum pulse width at startup?

You can find the starup operation at the datasheet 7.3.3, 'the first three switching-cycle current peaks are limited to IPP(min) to monitor for any initial input or output faults with limited power delivery '. 

First of all, thank you for your answer. And now I have another question that how can I determine the value of VVDDNL in Equation 32.

Is it the output voltage I expect？