input dc power rate of rise for LNK6777

Posted by: bougnoul on 05/19/2015

I think my msg got lost that I posted a moment ago. Here it is again.

A quick question: what is max rise time for the input DC source for proper functioning of the LNK6777 chip?

DC bench supply I have goes up to 250V in approx 250 ms
Is it not too slow?
Do you think the controller will shut down switching if it is so slow?

The input goes up is less than 2ms in applications where it will be used,

Appreciate a prompt finding of an answer for this question.
-robin'

Comments

Hello,

Slow increase of input is not a problem. The Line UV detection feature of the Link-HP will ensure that switching is enabled for sufficiently high input voltage so the power supply will maintain regulation only if the input voltage is adequately high.

Thanks and Regards,

PI-Sarek

Ok, that is good news.

I still blew up another controller. Typically, it just pops.

Yet, nothing was happening. The drain had 2 very short pulese...maybe less than 1usec many ms aprat. DC level was 100 v with 2 such pulses but of very high value...maybe above 600V. These so short pulses the clamp circuit would not clamp. I powered the dc source off & then on to see if the controller will start up. Nop. the chip popped right away. With so little energy in the pulses.

If the chip does not stay operating, one cannot trouble shoot. I know from external mosfet, external drive with the transformer I built , all my waveforms + divided down voltages look all ok. I am following PI_designer values.

So I have to give up trying & use some other chip.

I got no solution for 5 months for this small 12w flyback!

Hi,

Sorry to know about your difficulty is getting the circuit to start.

It is difficult to know only from the description about the exact source of the problem.

I will be gald to help if you can provide the schematic, layout and transformer design.

Best Regards,

PI-Sarek