Resistor Rfwd Failing

Hi Sreenivasan.M,

When the Rfwd resistor failed, does it damage also the IC? 

Can you provide us with the following during 180Vac:

1.  PIXls (spreadsheet and transformer construction) and layout.  
2. Capture waveform across the Vds of the Innoswitch and secondary FET (part number)

We would like to review your design on our end. 

Regards,
PI-Nanoe

Hi PI-Nanoe,

1. Yes IC is also failing
2. Find attach Files

3. FET part no FTB18N20, 200V,18A, 0.18E, D2PAK (TO-263)

   Observed SRFET Drain voltage is varying from 54V to 90V

    

   regards

   Sreenivasan M

Hi Sreenivasan.M,

Based on the waveform you provided; it seems that the switching is normal and way below the 150V of forward pin. 

Regarding the PIXls, I would not recommend using 100kHz as a switching frequency. You may encounter overload detection when you full load the power supply. Take note that the minimum overload detection of Innoswitch3-EP is around 102kHz and a jitter frequency of 1.7kHz. 

Can you provide us with the schematic and gerber files? I need to check further the traces and circuit implementation. 

Thank you.

Regards,
PI Nanoe

Hi Sreenivasan.M,

Based on the waveform you provided; it seems that the switching is normal and way below the 150V of forward pin. 

Regarding the PIXls, I would not recommend using 100kHz as a switching frequency. You may encounter overload detection when you full load the power supply. Take note that the minimum overload detection of Innoswitch3-EP is around 102kHz and a jitter frequency of 1.7kHz. 

Can you provide us with the schematic and gerber files? I need to check further the traces and circuit implementation. Your encountering seems not the typical behavior where the lower input Vac causing the damage. I assume there failing in the secondary why forward pin damages at this input voltage. 

Thank you.

Regards,
PI Nanoe

Hi PI-Nanoe,

Find attached files Gerber (KiCad 6.0), SCM & new PIXI sheet with switching frequency 68KHz.

Note: Output Over voltage protection circuit D9,D10 & R22 was not assembled in Proto PCB.

regards

Sreenivasan M

Hi Sreenivasan M,

Thank you for the additional details you provided.

Based on the schematic, it seems fine. Just a comment regarding the output capacitance, normally we use the standard 100-200uF/A for the value somewhat 2000uF is too big though still ok since it is working. 

For the layout, I have some comment, please see attached file. I would recommend optimizing first the layout.

On the other hand, can you please provide us with the following:
1. waveform across the Vds and Ids of the Innoswitch. We would like to confirm that it is not failing first. If you can provide waveform before it fails that would be great.
2. Datasheet of the core used. I would like to review the core characteristics. Based on the PIXls you provided, the nH/turns^2 should be around 7600. If too low, stress on the core may introduce unwanted behavior (thermal issue and saturation) that may fail in the primary side.

Thank you.

Regards,
PI Nanoe

Hi PI-Nanoe,

1. Waveform of Vds is captured, for Ids we don't have current probe
2. AL value of core is 518nH

3. Observation on layout, file is not sent

   we are closed from tomorrow  & will be back on Monday 4th Nov.

regards

Sreenivasan M

Hi Sreenivasan M.

With regard to your design, I strongly recommend to optimized first the layout in your design, please see attached file for the important items that need to address first in your design.