Hi, I think at start up full load + output capacitor charge current reached top chip max current limit. Is it damaged or unlimited restart? Sadik,

There is no damage and it restart several times before I turn off the power. Thanks, Maxjason.

I take two output capacitors off, only one 1000uf 35V capacitor left, it can start at full load. thank you very much, but there is one more problem, the noise. the p-p voltage is 4V, my output voltage is only 27.6V, how to reduce the ripple and noise. and, how to connect the probes of scope to the output, does it need RC filter between probe and output?Thanks again, Maxjason.

Hi, You should use a LC filter.

Hi, Sadik, you mean the output inductor and capacitor? or I need add another LC filter? Thanks.

Hi,

In order to protect the components of the power supply during overload or short circuit at output, most of our parts feature "auto-restart". If the output fails to reach regulation typically within approximately 30 to 40 milliseconds(if a 47uF capacitor is used on the C-pin), the power supply will enter auto-restart. during Auto-restart the power supply will stop switching for approximately 2 seconds and then will start switching again. However if output fails to reach regulation in the stipulated time, auto-restart will be entered again.

In some power supplies this happens due to a large output capacitor which prolongs the time required to reach regulation.

In such cases use of a soft-finish circuit solves the problem.

Figure.42 on page 22 in the TOPSWitch-HX datasheet shows an example of a circuit with the soft finish characteristic made using D6, C19 and R23. At startup, as the output voltage starts rising, C19 charges through D6 and the optocoupler diode. This results in a current in the optocoupler transistor. With the feedback loop closed, the power supply does not enter auto-restart as long as there is current flow in the optocoupler. Once the output voltage reaches regulation limit, the current flows from the optocoupler to the TL431 and capacitor C19 charges to the output voltage through R23. This meahcnism ensures that even for relatively slow rising output voltages, there is enough current slowing in the optocoupler to prevent the circuit from entering auto-restart.

When the power supply is turned off, C19 discharges through R23.

Please see datasheet page no.8 and Figure.11 for reference.

I hope you find this feedback useful.

Regards

PI-Sarek

This feedback is very useful. thank you so much. but now I have another problem. my power supply has to output 5 times output current for 16ms during 500ms period or 10 times output current for 16ms during 1s, that means, it has to output 25A for 16ms during every 500ms or 50A for 16ms during every 1s, the voltage can drop to average value 16VDC. my power supply can not realize it. it always shut down when current is more than 10A. I have no idea how to realize it? Could you please give me some suggestion? for my power supply, input is 120VAC, output is 24V, 5A. Thanks, Regards, Maxjason