Solution Finder


Posted by: boopathim@embe… on Tue, 03/30/2021

Power supply working fine upto 120Vac input. If increase more than 120Vac, than output will drop to 1.25Vdc from 12V.

FYI, I'm using INN3676C-H602-TL IC, designed for 85-265VAC input and 12V/2.5A output.

What is the possibility of error in this case? Kindly suggest us, idea to rectify this issue.


Submitted by PI-Bolt on Fri, 04/09/2021


Let's try to narrow down what part of your design may be the reason for this issue.

1. What is the load current when this issue presents itself?
2. What is the BPP and BPS voltage when the output voltage is 1.25V?



Submitted by boopathim@embe… on Mon, 04/12/2021


Thanks for your reply.


1.i'm design system for 12/2.5A output. but load is only 2A.
While am i check there is no load in output. It's just open ended.

2. While output voltage drop, All the IC pin voltage are down to minimum level.
Upto 120Vac input, that IC pins voltages are maintain as per datasheet. working well.

Submitted by PI-Bolt on Wed, 04/14/2021


1. To clarify - this issue presents itself when the load current is 2A, correct?
2. To clarify - what do you mean by "minimum level"? Can you measure the BPP, BPS, uVCC voltage when the issue presents itself?
3. Is current sensing being used? If so, what is the value of the current sense resistor?
4. When this issue presents itself, is the converter in a steady state operation? Or does this happen during start-up?
4. Are you using a PI design as a reference? Or is this a completely custom design?

Submitted by boopathim@embe… on Fri, 04/16/2021

1. I'am not using any load in power supply output. Power supply output is open ended.
2.Minimum level- nearly equal to zero. BPS,BPP & all pin voltage also goes to zero when issue present.
3.I'm checked in both method. With current sensing and without current sensing method. With current sensing method, I'm using 10mE resistor.
4.from 80V to 120Vac input converter is working properly, then increase more than 120Vac converter is not working. All pins voltages goes to nearly zero. except V pin,because it's direct input pin. In V pin voltage measure nearly 160Vdc during output drop. FYI,Also if use BPP pin current enhanced mode(4.7uF), then working upto 130Vac.
5.Yes I'm using PI design as reference.

Submitted by PI-Bolt on Fri, 04/16/2021

If the BPP voltage drops to zero volts after increasing the input line voltage from 120VAC, then an overvoltage event is NOT being triggered. If the BPP capacitor is at 0V, then this means that no power is being provided to the INN3676C.

1. This can be confirmed by looking at the output voltage with an oscilloscope - is the part entering an auto-restart event? Or is the output voltage continuously at 0V?
2. May you share your schematic for review? Or can you provide the PI design used as a reference to get an idea about how your system looks?


Submitted by boopathim@embe… on Mon, 04/19/2021


Thanks for your reply.

1. It entering into auto-restart event.. If give more than 120Vac then output will slowly decreased to 1.25V from 12Vdc. Not decresed below 1.25V. Also FYI, If I return or reduce below the 120Vac input voltage, then system will auto-restart work in perfect.
2.PI reference design generated based on below criteria, Input 85-265V universal input, Transformer E25/13/7 core, output is 12V/2.5A,INN3676C choose, For bias and primary diode is UF4007. I think this information is enough for you.


In your earlier post, you mentioned that the BPP voltage goes to 0V.  However, in your latest post, you mention that the output voltage decreases to 1.25V.  If the BPP is 0V, this means that the controller is not being powered. So the 1.25V you measure at the output may be residual energy in the output capacitors, or there is something else in your system connected to the output.  Can you measure the BPP and BPS voltage when the output voltage is 1.25V and share an oscilloscope screenshot?




Submitted by boopathim@embe… on Tue, 06/29/2021


Sorry for late reply. Due to lockdown here, Not able to test. So, Not able to give you reply. 

Kindly find the attachment in reference PI design.

Now current problem explained in below,

1. Upto 110Vac input - Working stage with proper output -12.28Vdc - (while BPP voltage - 5.4V & BPS voltage -5.4V & FB -1.4V)

2. Above 115Vac input - Output voltage drop and oscillated in between 0- 1.25V (while BPP voltage - 5.4V & BPS voltage - 0 V & FB -0V) (All secondary voltage slowly discharge to zero)(Note- tested up-to 3-5 minutes)


Attachment Size
reference PI design 252.19 KB
Submitted by PI-Bolt on Tue, 07/06/2021



  1. For the output voltage oscillation - what is the off-time when the output voltage is 0V and on-time when the output voltage is 1.25V?
  2. What is the current conduced by R6 at 110VAC input?



Submitted by boopathim@embe… on Mon, 07/12/2021


we are using R6 value is 5.23kohm as per mentioned in reference schematics. Transformer primary bias voltage will be 13.5-14.3V, When input is 80-114Vac. Above 115V, bia voltage drop to 5-7V range. current conduced nearly equal to 2mA.

FYI, Transformer winding details, 1&3 wind -959uH, 4&5 wind -9.9uH, 6&7 wind - 7.4uH

SR MOSFET P/N: AON6262E instead of schematic P/N.

Kindly suggest us,details to rectify this issue.


Submitted by boopathim@embe… on Tue, 07/13/2021


Kindly find the attachment in Output capture waveform.

In waveform, Upto 114Vac input- Output will be stable. If increase voltage more than 115Vac input - Output will be suddenly decrease.


Attachment Size
Output voltage capture.jpg 3.75 MB



To clarify - when operating above 115VAC, what is the voltage across the R6 resistor?  We need to know the current at the time when the output voltage is not regulating to the nominal. 





Submitted by boopathim@embe… on Tue, 07/13/2021


FYI, When operating above 115Vac,  R6 resistor across 5.44V measured. 

While operating below 114Vac, R6 resistor across 14.3V measured.

FYR, kindly refer transformer specification datasheet in attachment.

Awaiting for your quick reply, Already long delayed in process.


Attachment Size
transformer datasheet_0.pdf 323.5 KB
Submitted by boopathim@embe… on Mon, 07/19/2021

Dear sir,

Kindly find the attachment in transformer waveform capture details.

Capture details mentioned in capture name. All way of possibilities checked, no improvement.

Is anything wrong in schematic or transformer design?

Otherwise locate problem happened area in schematics. We will check and improve that area.

Awaiting for your reply.

Attachment Size
All conditions capture signals -FYR 3.96 MB
Submitted by PI-Yoda on Wed, 07/21/2021


please load the unit with 50% load and repeat the test.


Submitted by PI-Wrench on Tue, 07/27/2021

In order to home in on the problem, I suggest using a current probe to look at the drain current at an input AC voltage just below where the supply shuts down. This will help to determine whether the supply is shutting down due to excessive drain current. 

In addition to that, I also suggest  monitoring the voltage at the drain of the synchronous rectifier (M1 on the supplied schematic). The sync fet drain voltage should be positive during the Innoswitch on-time.

It is also a good idea to check the waveform on the cathode of the primary bias rectifier (D6). This should also go positive when the primary switch is on. If the transformer is accidently mis-phased (either the secondary or the bias winding) it can cause problems similar to what you are experiencing.