TOP266KG minimum input voltage

Posted by: aquerido on 05/15/2019

Good day to all
I have started working in a company that already had some designs made with the CI TOP266KG.
Recently, I have detected that in the power supplies designed with this IC, the minimum starting voltage is 21.5 V when the one previous version of the same design starts from 15V.
Comparing the new version with the previous version, I realized that the capacitor C254 of the attached schematic, in the previous version was an aluminium electrolytic, and in the new version it has been replaced by a ceramic one.
I have verified that if I weld an aluminum electrolytic capacitor in this position the problem is solved.
But, I would like to understand why does this happen.

I attached a screenshot of the oscilloscope at the time of start-up in capacitor C254.

Can someone help me with this topic?
Thank you

Files

TOP254.pdf (958.13 KB)

TEK0005.JPG (78.71 KB)

Comments

Hi aquerido,
I saw in your waveform that the ceramic capacitor caused a very high low frequency ripple voltage. Capacitance of Electrolytic capacitors are more stable than ceramic capacitors which makes it more stable in having clean voltage ripple. Since TOP C-pin requires a clean and stable voltage reference, it is best to used electrolytic capacitors.
Regards,
Jedidiah

Thanks for your answer, I will use electrolytic capacitors for this position from now on.

BR
Alvaro

We have recently modified the equipment that charges this source, increasing the current demand.

We have observed that the minimum work input voltage depends on the power demand.

According to our tests to be able to work at the minimum input voltage (18V in "DRAIN Supply Voltage" the maximum current at the output of 5V is 1.3A.

We would like to be able to increase the maximum output current to for the minimum input voltage (18V).

We believe that a solution would be to modify the turns ratio of the transformer. Now it is 44:19:8 (Primary:Auxiliary:Secondary)

I have tried to simulate the solution with the pi-expert WEB application but I cannot because it does not let me apply a voltage lower than 32V DC as an input parameter.

Could you help us to get to increase the maximum current?

Attached the latest version of the power supply schematic. "TOP266KG.png"

Best Regards

Alvaro

Attachment	Size
TOP266KG.png (134.95 KB)	134.95 KB
TOPSwitch-JX_possible 3.uds (310 KB)	310 KB
ESPECIFICACION TOPSwitch-JX Flyback (266KG)_12W.pixls (42.48 KB)	42.48 KB

Hi aquerido,

It will be challenging to design at 18V especially with higher power/current. We have soft start timer during start-up and If no external feedback/supply current is fed into the CONTROL pin by the end of the soft-start, the high-voltage current source is turned off and the CONTROL pin will start discharging in response to the supply current drawn by the control circuitry. You can try increasing VOR if it will help....

Regards,

Jedidiah.

Hi,

I am facing same issue with the TOP265 switch.

I have already design one smps Input 19.2 to 373 VDC Output 12V 3W.

Now I am trying to increase the power till 5W.It is working fine with higher voltage but not getting turned on at 19.2 and even if it turned on it will shutdown after some time.

Is it not possible to work with lower input ?

Is there any way to work this out with higher rating switch ?

This is a design that might work - see attached PDF file.

Don't let the 10000 uF cap scare you - that's just there as a trick to generate a stable DC supply using an AC input. If you are using a real DC source, you're likely to need a 100nF-1uF bypass cap close to the TOPSwitch.

Attachment	Size
TOPSwitch-JX TOP266_5W DC input_1.pdf (36.77 KB)	36.77 KB