Input start up voltage problem

Posted by: katte swaminath on 07/28/2014

Dear sir, I am designing 20-40Vac/20-60VDC SMPS using TNY280. I have attached design and observations file.I am facing problem at 20VDC input voltage, it starts at 20.6VDC instead of 18VDC. Please go through the design and observation file and suggest any modifications to overcome the problem. Thanking You, Regards, Swaminath katte

Files

Schematic_12.pdf (49.84 KB)

SMPS_design&_observation data.xls (15 KB)

Comments

You need to implement your circuit with the CC described in the below link http://www.powerint.com/node/234

Is it possible to solve this problem by using other core size?

When starting the power supply at 18 volts, you do not have enough current inside the chip to charge the BP pin capacitor. (Charge is coming from an internal CC source connected from DRAIN to BP pin). The internal CC does not work when VIN is too low. So you need externally charge the capacitor for your controller for it to run.

Thank you !