SMPS start-up problem
Posted by: ilkeraltay
on
Hi,I use your PIexpert program and design SMPS.I have a problem with startup.My load can be simulate like 50000uF capacitor and parallel 39R resistor.Initialy all capacitors is empty,so when the power supply is connected it pulses.Schematic and transformer specs are attached.
Regards.
Ilker ALTAY.
Comments
Thank you for reply.The supply works with resistive load.I tried with 100uF capacitor on the control pin.But problem continues.
Try putting a 100uF electrolytic capcitor across TL431 and perhaps increase 47uf capcitor on control pin to 100uF (or more). Your problem is related to the long start-up time before reaching regulation. These two changes allows the control pin to be biased before reaching regulation and avoid auto-restart hiccup.
I put 47uF electrolytic capacitor across TL431 and the problem was solved.Thank you.
I can think of 2 things that ay be happening
1) There is a problem with your feedback loop. It is probably open which is why you see the pulses (auto-restart)
2) Does the supply work with a resistaive load? If yes then there is no problem with the loop. The problem is that the loading is highly capcitive, which results is a large start-up time. With a 47 uF cap on the control pin the output should startup within (approx) 47 ms. Try using a 68 uF or 100uF capacitor on the control pin to see if this soves the issue.