Hi, Suk Chan Song,

Good day. The BPP must be observed to be around the specified BPP Shunt Voltage, which is around 5.36 V. We can start from this point by reconfiguring RBP, which is R3 in your schematic. For further review, we would like to ask for your transformer construction.

I look forward to your response.

Thank you for comment.

I attach the transformer construction.

We copy the PI expert online magnetics Designer.

Turn ratio is 21:5:2 (Prr:bias:sec)

and the Lm is 180uH Lk is 2.8u In 100khz

Also What is FWD pin?

This charge the BPS cap? 

And what is normal volagate of FWD pin and FB pin

Plus the INN3278C-H114 can CV mode?

We are  use E-load in CRmode that 1.25oHm and V limit is 5V I limit is 4A

Our goal is 20W (FULL LOAD 5V 4A)

                                 (50% LOAD 5V 2A)

thank you

Hi Suk Chan Song,

Thank you for your immediate response.

Upon further review of the schematic diagram provided, the following items were observed:

1. The secondary capacitor clamp, C7, is too high with a value of 150 mF; we suggest decreasing the value to 470 pF to 4.7 nF.
2. Feedback resistors R6 and R7 are too low and calculated to not obtain 1.265 V for the feedback pin. We suggest configuring the FB pin with the following values:
RFB_UPPER (R6) = 100 Kohm
RFB_LOWER (R7) = 34 Kohm

And for your questions, please refer to the following:

Also What is FWD pin? This charge the BPS cap? -
It takes switching information from the secondary rectifier to monitor cross-conduction, and yes, this charges the BPS when VOUT is below the threshold that is set by the FEEDBACK pin.

And what is the normal voltage of the FWD pin and FB pin?
The FWD pin normal voltage should be the calculated PIV of the secondary, and it is rated at a maximum of 150 V. And for the FB pin, the normal voltage as mentioned above should be 1.265 V. 

Plus the INN3278C-H114 can CV mode?
Yes, the InnoSwitch3-CP operates in CV mode.

I hope this works for you. Should you require further support and clarification, please let us know.

Thank you for comment

our construction is 800uF MLCC output cap

and BPS Cap is 1.5uF, BPP is 0.47uF and resistoris 2.2K

we fount that the primary swiching sequence is 25Khz but they auto-restart 1.8sec

I think this working is the feedback pin didn't sensing the voltage so secondary switching is not work

is it right?

Hi Suk Chan Song,

I appreciate the quick reply.

We recommend output capacitors be electrolytic, as this is suitable for high frequency switching power supplies.

And for the BPS cap, thank you for providing information on its current value of 1.5 uF. In comparison to the schematic diagram, your BPS is C6 and has a value of 220 uF. Both values were not suggested. We suggest using a 2.2 uF capacitor as the BPS cap, as recommended in the device design guide on page 16.

The 25 kHz observed is the softstart frequency of the device and is normal; since there is a fault sensed by the device, it will remain as is with every restart and won't increase until the fault is fixed.

Yes, you are right. If the FEEDBACK pin does not sense the right regulation on the output, the device fault protects the system by auto-restarting. 

I hope this resolves your inquiry.

Then how can i solve the 1.265Vdc in feedback pin?

This is relate with secondary bypass cap?

When the Under register is measured with an oscilloscope nothing show

How can i measure the 1.265 V in feedback pin

Hi, Suk Chan Song,

The fault sensed by the FEEDBACK pin is reconfiguring the feedback resistors, which in your case are R6 and R7. As mentioned above, you may change the values as follows:

RFB_UPPER (R6) = 100 Kohm
RFB_LOWER (R7) = 34 Kohm

The BPP cap is another issue that might also be affecting the signals measured by the secondary device. We still recommend using 2.2uF.

To measure the FEEDBACK pin, you place voltmeter across R7.

We don't have 100K and 34Kohm so 

we use 62K and 21K 

can you repeat me what this waveform mean?

The yellow is Vds

Purple is BPP cap voltage

Blue is bps voltage

Green is FWD resistor 47ohm voltage

Hi Suk Chan Song,

Could you confirm if my assumption is correct: 62 kohm is for R6 and 21 kohm for R7?

Regarding the waveforms, it appears there's auto-restarting and BPS discharges, which shouldn't be. Have we increased the BPS capacitor from 1.5 uF to 2.2 uF?

Yes 

R6 is 61K and R7is 21K

and BPS is 2.2uF

If could be transformer problem?

Have you seen a case like ours?

Hi Suk Chan Song,

Thank you for confirming.

Yes, we've seen cases like this, and it usually causes faults sensed from the secondary section. 

Possibly it can be caused by the transformer. Would it be okay if you could provide the PI Expert on which you've based your transformer?

We could also consider using an electrolytic capacitor on the output. 
 

Hi

Our problem is the tramsformer

We use 280uH (Lm) and it work

But the input voltage is 219.92V and current is 0.252mA

Out put is 5v and 4.99A

The input current is so high

How can i reduce the input current ?

This is a power supply with no PFC front end, so the power factor will likely be somewhere in the region of  0.6-0.7. This means that the apparent input current (and resulting input RMS current) will be high. There are solutions for this, but they will increase the parts count. 

This design example uses "valley fill" power factor correction, which can reduce the input current. Perhaps you can adapt the circuit with larger capacitor values for use with your design.

https://www.power.com/design-support/design-examples/der-423-12-w-power-factor-corrected-valley-fill-non-dimmable-isolated-led-driver