UC1845A: Observed high frequency kind pulses in drain to source

Thanks for the response sir.

But I am facing this when i put 3A of load at 230VAC input so as per calculation for 190uH as per calculation for full load current of 7A i am getting primary inductance of 285uH. so the present inductance is less than the critical inductance. but dont know why its happening like this. And doesnt the three pulses seems like having higher frequency than the oscillator. and if its in border it should not effect the frequency right.?

thanks kindly help with this.

Hi Kindly Find the I doubted something in the RT CT so i observed that Something peculiar. If you observe the RT CT is not correct i am observing smalll ram. could you specify why might this happen. Find the waveform images wit the titles

 2845.Waveforms.zip

Kindly Find the Pdf where the input uv/ov protection and over temperature protection is disabled .

this is the circuit and the ic is UC1845AMDREP

And Lp is 160uH turns are Np 30 Ns 6 Na = 6

And SWITCHING Frequency is 57KHZ AND OSCILLATOR IS 113KHZ

Thanks

Blue is RT CT pin  of uc1845A. and yellow is VDS

To avoid this I have changed the IC to UC1843A(100% duty) to suppress this issue

Now this issue is solved I am getting new issue 

Above is Blue cs and yellow vds.

I am getting this spike in the on time. What might have caused this.

Is it noise will it be solved if I add some caps in vref or vdd

This is blue - gate of MOSFET yellow vds

Find these waveforms for your analysis. As for the schematic i already shared it in the previous replies. kindly look into it.

B

Blue is comp and yellow is vds

Here click on the 15V 7A 

1134.15V 7A.pdf

Hi Now I have changed the kelvin contact resistor at the gnd seperating power and signal from 0 to 30 ohms Now its working fine i am not facing this kind of pulses. but only at 90VAC input i am facing this issue.

why is that could you help me with it

I found one observation that when I increased the kelvin contact ground resistor. from 0e to 30E near the controller IC the is gone now working fine.

I want know how it effects the Converter.

find schematic

They are the values i updated of kelvin resistor used between primary power ground and signal ground 

e means ohms, just like 10R ,20R some time we use 10E,20E like that.

thanks but can you say how changing the kelvin contact resistor helps in the resolving of issue

This problem typically occurs due to the MOSFET exceeding its overcurrent limit. The Kelvin resistor helps increase the MOSFET’s slew rate and reduce the current during turn-on. The best solution is to increase the gate resistance.

thanks mr DSR how can i personally contact you. so you can guide me.

Contact me through this linked in

linkedin.com/.../devaraj-s-156a32117