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TOP266KG Quality issues?

Posted by: fulignani@alma… on Wed, 06/16/2021

Good Morning,

I'm facing with a problem on a Flyback power supply realized with a TOP266KG

It is in production by 2 years ( About 8000 Pcs ) without any problems, but right now we found 3 devices that are behaving in a weird way.

The PS it is a 10W 20-265 wide input range PSU. It is working as desired, all devices starts in a range 16Vdc 19Vdc and gives full power @20Vdc. (The data sheet declare that the IC start @18Vdc)

A couple of weeks ago we found an IC that was starting only @40Vdc or more....once it is started all of the waveforms and the characteristics were correct.

To verify that was not a PCB/component issue we just desoldered the IC and replaced with a new one. THE PSU then worked as specified.

The drain waveform below the 40Vdc was just the DC lines without any attempt to start the PWM modulation.


The second one today. This IC start randomly, and works for some seconds....then goes off, and there is no way to restart it. After a while, it repeat the process...some seconds of normal working, then it goes off. 

Once changed the PSU worked fine.


The third one was constantly repeating the bootstrap procedure. Short circuiting the resistor on the X pin with a tweezers force the IC to work fine for a couple of seconds.

Once changed the PSU worked fine.


Two ICs have the same top marking  TOP266KG  1721  6A535C and one TOP266KG 1721 6A468(B)? It seems a B.


We use to do a first test @16Vdc and a second @24Vdc ( We saw the problem at this stage). Then, if they work fine we start with a full spec. test.

This is to specify that these devices never saw more then 40Vdc.

I kept the 3 ICs in an anti-static box if you need them we can arrange a shipment.


Thank you,






Submitted by PI-Wrench on Mon, 06/21/2021

For reference, can you share your schematic? 

Submitted by fulignani@alma… on Mon, 06/28/2021

Yes, but only in privat mode, it is a company policy.

Let me know where to send it.

Thank you.

Submitted by fulignani@alma… on Mon, 06/28/2021

Meanwhile we found two other devices with the problem.

We did some further tests, and we found that these devices start at 26Vdc, but then if we lower the voltage till 13Vdc the device stay on and work correctly.

It seem an hysteresis problem. We did the test with a 4W load and without load, but the behave it is the same.

Anyway, i want to point out that before the device start, there is a flat DC voltage on the Drain, so the device it is not even attempting to start.

We did a further and interesting test:

We have removed from the pcb the transformer, and the optocoupler leaving the TOP266 alone.

This is the TOP266 config:


Pin 1(V) Connected to GND 

Pin 2(X) Connected trought a 12.4K Resistor to GND (Tested as 12.38K )

Pin 3-4 floating

Pin 6 18 Vdc

All others pins to GND

Then we put 3 TOP266 from a new reel and all of them started the modulation on the Drain.

Then we put the two non conformal devices on the same PCB, and none of them started the modulation till we raised the Drain voltage to 26Vdc.

This is a problem, because we have some markets where the customer use them at 24Vdc, that sometimes it is a 22 Vdc. 


Thank you. 


Submitted by PI-Wrench on Mon, 06/28/2021

At this point, it's probably best to send a message to rma_at_power_dot_com to start a review process, especially since you have additional failures.