Switching Frequency

Hi,

What is the test condition when you get 3kHz switching frequency? Would you please show me the waveforms?

Thanks 

Sorry sir I got the output. Switching frequency is coming fine but still there is ripple in output voltage.

I have attached two waveform Drain to source voltage and output voltage respectively.

What is the minimum voltage where the Switch will turn on?

Hi,

Some ripple voltage is expected to get in the output, if it inside of the spec, it is okay.  

If you design the power supply with under voltage funciton with the resistor on the V pin, then the voltage that enable the switching will depending on the resistor value that you selected. You can refer to the data sheet or application note for detail calculation.  

Hi,

thanx for ur reply.

The ripple voltage is not within the limit,but that is the secondary thing .

Main problem is that I can not go to the minimum voltage (that is 90 volt Ac) . I told you before that ,i am using Auto transformer for Ac supply, but when I reach upto 30 volt ,it is making a huge sound .

I guess that I am using only capacitor at the output of rectifier ,so may be due to current it is happening.

So to rectify it, I used inductor of 2 mH , but more spikes is coming across switch .

I have attached the switch voltage (Drain to source) waveform

Hi,

If I understand well, you notice the audible noise issue when the input voltage is 30Vac, is it correct?

If the design for the power supply is 90Vac minimum, would you please try with 90Vac input, what happen?  

 Now it is working fine,I applied upto 100 volt.The problem was due to Rectifier, so more current was flowing. That problem was solved.

But again that switching frequency problem came. Switching frequency is coming nearly 3Khz.

I can not understand ,why this type of problem is occuring.

Another thing the duty ratio is coming 70 % , and the desired output voltage is not coming.

 I have attached the waveform of voltage across switch.

The input voltge is 100 Vac and required output is 24 volt,but nearly 10 volt is coming.

Sorry , Duty cycle is not 70 % , it is 30%.

The output voltage is coming nearly half of thr required voltage.

Please give some suggestion .

Hi,

Thanks for the waveforms, I saw that you use the scope measurment function to check the switching frequency, which is not always correct as the dv/dt is very high.

Would you please expand the drain votlage waveforms, and use the curse to measure the exact switching frequency? I do not think the switching frequency is 3 kHz.  

No sir

The switching frequency is coming 3Khz.

I have attached the waveform.

Another thing sir, I didn't take the supply for Optocoupler from Bias winding, is there any problem?

I am getting half of the desired output voltage

Hi,

There is no possbility for the power supply works under 3 kHz switching frequency except under fault conditoin.

Back and force, I saw you said the switching frequency was fine, why it is not normal again, what is the change that you made? I saw the schematic, the bias winding is provided to supply the optocoupler, it is different that what you said here. Did you make any changes on the schematic too?

Another point is TOP 227 is an osbsolete part, do you have any plan to replace it with our Top Switch JX or HX? 

First thing I could not get any difference between Bias Winding and nirmal Secondary winding.I have tried with both , but there is no difference.

Another thing Switching frequency is not  3 Khz, It is flactuating. You are right that , Switching Frequency depends upon the oscilloscope setting. So no problem about that.

My problem was Output voltage, Now when I am increasing the Resistance R1 value (to decrease the current)  the output voltage is also increasing,but it's a problem to get perfect R1 value. Because If I am increasing the Input voltage ,the output voltage goes on increasing. So I need one perfect value of R1.

I don't know about Top Switch JX or HX, whether it is available here or not . 

If this is new design, I will recommend you to use the TOP-JX and HX.

You could put a resistor in parallel with the opto-coupler LED, if you can not find a good resistor value for R1.  

How much resistance should be used in parallel?

Thank you for your suggestion. I will try Top JX or HX.

But now I have to complete this with Top227.

Hi,

You could try a 1 kohm resistor.