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Primary Bias Winding

Posted by: Harshit on Thu, 07/08/2021


I start to design on INN3672C. In my application, I need 11V, 700mA output (+/- 100mV ripple volt is ok)   and input volt will be 200V AC to 265VAC. There is no power constrain on mains input.  My question is

1. what is the role of the primary bias winding ? 

2. can I design without the SMPS without primary winding ? what things to be change in this case ? 

Please help me to move forward. 


Submitted by PI-Sky on Tue, 07/13/2021

Hi Harshit,

1. The role of the primary bias winding is supply the primary bias pin (BPP). Using a bias winding will lower the power consumption and the overall temperature of the IC since the BPP will get its supply from the internal regulator when there is no bias winding.

2. If what you mean is if you can design SMPS without a primary bias winding, then absolutely you can do it. You can just do it similar to this(figure 1). If you're using the PI XLS, you can just ignore the primary bias winding in the diagram (remove it from the transformer). 

Figure 1. Flyback w/o bias