Ringing in flyback PS.

Can you post a scope shot of the waveform showing this ringing? There is probably no need to damp this ringing. Careful use of shield windings in transformer as per PI Expert will prevent any EMI issues.

Also if you reduce the capacitor value by 100x and increase the R value by 100x, the dissipation will be 0.23W.

hai This is pavan i am also facing the same problem ringing drain to source pls tell me how to reduce this ringing issue.

Hi pavan.kumar,

Can you upload your schematic and Drain Voltage and Current Waveforms? Thanks!

Regards,
PI-Pike

Hi i have attached the wave form .i designed the 60v/3amps with the reference of P.I i got the stable output voltage . but i need cv/cc configuration .with the reference of der580 document I made the cc/cv circuit . my problem is i am not understanding the working of cv/cc circuit in der580 it is designed for 59/2amps, 66KHZ . i need to increase 2amps to 3amps. and 132khz plseas tell me what changes have to do . i choosed topswitch TOP261YN. for 3amsp all components i selected higher rating values .for 132khz is it to change transformer design/ to otherwise can i shot F pin to C pin . please help me

MyP.I schematic is 60v/3amps 132khz attached . with the reference der580 is 59v/2amps 66khz.I made the cv/cc circuit for my P.I schismatic is working but some doubts are there . how the cv/cc circuit works

Hi pavan.kumar,

Thanks for the schematic and waveforms!

I think this is a problem on the snubber or the layout of the snubber loop. To reduce the ringing you could adjust the frequency of your primary snubber or minimize the layout of your snubber loop.

If you want to have a 132kHz you should connect the F-pin to the S-pin also change the transformer design. You could also short the X-pin to S-pin to disable the current limit, it can go to 3A. Attached is a sample of PI-expert file (60V,3A).

Regards,
PI-Pike

Thanks for your replay . when i connect more than 1amps load output voltage going to drop 60v to 40v . pls tell me what is the problem.

The primary side inductance of your transformer is now too high for the extra load...

in the circuit clam resistor getting very hot when connected the load .tell me how to reduce.

R6 Resistor getting very hot . i changed r6 value to 100ohms but same issue . transformer leakage inductance is 10uh with all winding shot. primary inductance is 136uh as per the PI expert sotfware. and so much ringing in drain voltage . i connected 1.8amps load 60vdc. at 1.8 amps load pls find the drain to source waveform . pls tell me is that waveform is ok or not. ringing will affect the the circuit. pls its important for me

Hi pavan.kumar,

The waveform is correct because it is free-wheeling at that load.

To reduce the heat try increasing the value of snubber resistors or increase the wattage resistors.Reduce the value of the snubber capacitor to reduce the energy.

Regards,
PI-Pike

Thanks for your replay i tried to adjust the clamp resistor value if i increase the resistor value 47k more ringing on drain waveform .and peak voltage going high nearly 300v you can observe in waveform .pls tell me how to fix this issue .

i am trying der580 circuit in this when ac input voltage is 180v .output going to 140vdc. within 5sec mosfet burn .tell me how to reduce the output voltage to 60v . i attached the schematic pls find

pls tell me clamp circuit/ Snubber circuit design with example

Hi pavan.kumar,

Could you try increasing the R4 to around 200k (parallel 2 to 3 resistors with high wattage). 33k is too small, high energy will be stored on the transformer thus it will have an effect on the output regulation, you need a higher resistance to dissipate the energy on the transformer.

Could you also upload a picture of you power supply to see the layout? Thank you!

Regards,
PI-Pike

Hi with the reference of the der580 i made the circuit. I got the 5ov output. But when I connect the load 500mamps .output voltage is going to drop. 59v yo 30 v is droping .all resistor values are same as per the reference design der580. Pls tell me what may be the problem. Pls replay soon .

Sorry it is 59v

Hi pavan.kumar,

Can you please check the build of your transformer, see if it is correct? Pin assignments, polarity, inductance etc.

Check also the feedback part of your psu. C-pin connection.

Regards,
PI-Pike

Your transformer simply has too much leakage inductance, and your layout may be very open and not enough de-coupling on the HVDC...

Hai ,
i have attached the transformer specifications as per the PI .I got primary inductance is 122uh and leakage inductance is 2.4uh .designed transformer as per the specifications mentioned PI .when i connect the load output voltage goes to drop 59 to 30v . problem not solving .i have attached the pcb board and schematic and waveform pls tell me how to solve this problem. in the schematic output ground is not connected .i connected externally.

Hi pavan.kumar,

Thanks for the files! Can you please also upload a picture of your psu to see the layout?

I didn't see any problems on your uploaded Schematic and verified your transformer construction on PIXls.

Regards,
PI-Pike

I have attached the pcb layout (board). I changed R19 value 100k to 50k .after changing the R19value to 50k regulation problem is gone.pls tell me by changing this R19 value will effect the circuit. Thus lm358 circuit will work fine with out causing any problems while charging ?

I have attached the waveforms. Input voltage 150vac connected resistor load 33ohms output voltage 60vdc .I got drain to source waveform like this .is this waveforms ok ..snubber resistor R3 getting heat on load I connected 4 51kresistor in parallel plz help

VR2 = 160 volt - is this correct?

your o/p rectifier is a long way from the transformer - this adds to effective leakage...

this accounts for the excessive ringing at turn off of fet ... also lack of decoupling near the PI part...

After changing the R19 value to 30k output voltage is stable .no regulation fail.connected resistance load 2amps it is working good but when I connect 5 batteries in series to the output it is not working.again I connected resistance load it is working . Am not understanding the problem .Pls help me why it is happening like that

After changing the R19 value to 30k output voltage is stable .no regulation fail.connected resistance load 2amps it is working good but when I connect 5 batteries in series to the output it is not working.again I connected resistance load it is working . Am not understanding the problem .Pls help me why it is behaving

Too many batteries in series may be just above the volt setting on your circuit - hence the feedback loop will stop it...

Hi pavan.kumar,

What batteries did you used?

Regards,
PI-Pike

When I switch on the 150vac input supply directly without load drain peak to peak voltage going high 400vdc after 2 to 3 sec it is coming to normal position . But with load no problem . By using varaic input supply by increasing input supply slowly no problem with load. Pls tell me why it is behaving when I switch on input supply directly.

When you switch on suddenly the L in the variac rings with the input C of your circuit and the voltage resonates up to more than the peak input ( up to 2x is possible)

This is why some power supplies have an inrush resistor (ntc) or a relay and resistor...

1) Thanks for your replay . the above circuit i connected to the electronic load . electronic load voltage is 48vdc . current is drawing 2.5amps . output voltage is 55vdc. when i adjusted the electronic load voltage to 58vdc output current going to drop 0 amps suddenly . my question is that output current should be decrease slowly like step by step. like V-I characteristics but it is going to drop suddenly to 0 amps . for cc cv circuit i copied from der580 .

one more problem is when i switch on the ac power supply directly output going to 70vdc .but by using variac it is not going to 70vdc .it is maintain 60vdc why this problem happens.

pls tell me the how to slove above two problems .

with load it is not going to 70v dc .without load when i switch on the supply it is going to 70v

Hi pavan.kumar,

Check page 22 of this application note: https://ac-dc.power.com/sites/default/files/product-docs/an43.pdf

Add a diode-capacitor to form a soft finish network.

Regards,
PI-Pike

Hai thanks for replay .I need to connect cooling fan in the above circuit .I tried 12v o.12amps cooling fan .I connected to Q2 emitter terminal and also tried zener vr2 but regulation going to fail output voltage increasing .pls tell me from where should I take supply for cooling fan .and also I need to connect led indication like charger on and battery full indication pls suggest me how to do all this

Pls tell me from where should I take supply to connect cooling fan

Hi pavan.kumar,

You could use a comparator circuit, or zener diode for the LED indicator.

Regards,
PI-Pike

Hi, thanks for replay ,
The above circuit is working fine cv/cc configuration is also working good . but some problems are facing .
-> output voltage starts at 85vac without load. but, with load output voltage starts at 180vac. connected load is 2.5amps .but below 2amps output starts at 85vac.
->primary bias voltage after the diode rectifier without load am getting 20vdc.. with load bias voltage changes to 50vdc . input voltage is 230vac.
->without fan it is going to auto restart on 2.5 amps load. only 15-20 minutes output voltage is stable.but with fan it is running with out regulation fail continuously.

pls give some suggestions to solve this problems . its urgent for me reply me as soon as possible

Hi pavan.kumar,

These are my replies to each of your problems.

-> output voltage starts at 85vac without load. but, with load output voltage starts at 180vac. connected load is 2.5amps .but below 2amps output starts at 85vac.

-- At 85VAC try checking if the device is reaching power limit, check also the temperature of the IC. Try also increasing your input capacitance value.

->primary bias voltage after the diode rectifier without load am getting 20vdc.. with load bias voltage changes to 50vdc . input voltage is 230vac.

--I think this is not a problem operation-wise, but you should increase the voltage rating of your bias capacitor.

->without fan it is going to auto restart on 2.5 amps load. only 15-20 minutes output voltage is stable.but with fan it is running with out regulation fail continuously.

--What input VAC is this? It seems that you are reaching Over thermal protection. Might want to add more heatsinking on the IC.

Regards,
PI-Pike

Hai Thanks for your replay
i increased the input capacitor but no change same problem getting. and aslo i removed the X pin resistors R5,R6,R7. but no change . IC Temperature is normal .i connected the soft finishing circuit same problem repeating . below 2amps output voltage starts 85vac but above 2amps output voltage starts 180vac. pls give me any solution to reduce this problem . i want to take this in production .if it will complete successfully

->is there any calculation for soft finishing circuit ?
-> Tell me how to decrease/increase the optocoupler current .in the above circuit what resistor value have to tune .

Hi pavan.kumar,

To disable the X-pin (Current Limit), you should short it with the Source-pin.

Adjust R23/Rbias resistor to tune the optocoupler current.

Could you please also check the temperature of your secondary rectifier. Thanks!

Regards,
PI-Pike

X pin is shorted with source pin .it is Ok, but on 2.5 amps load topswitch temperature going above 100C going to and shutdown. Without fan .with fan topswitch temperature maintains 66C on 2.5amps load .I connected cooling fan externally from regulated power supply 12v .I want to take 12v supply from circuit. How can I generate 12v supply in circuit .pls give me any idea .I tried to take 12v supply from Q2 transistor output but output regulation going to fail.

Hi pavan.kumar,

Have you tried increasing the area of your Heatsink?

My suggestion if you want to use a fan is connect the circuit on the bias winding. But I think it will have an effect on no load condition.

Regards,
PI-Pike

Yes I increased the heatsink size .I take 12v supply from bias winding .it's working fine .1 more problem is when I switch on input 230v directly without variac mosfet blown. I think when I on 230v ac direct peak voltage going high. Pls tell me to Slove this issue .I tried soft finishing circuit but no change pls tell me exact soft finishing circuit values for the above circuit otherwise tell me the soft finishing circuit calculation

Hi pavan.kumar,

Please clarify, when using variac and set it to 230VAC it works fine, but when you connect it directly to 230VAC line without variac the mosfet blows up?

For the soft finishing circuit just use components within rated values.

Regards,
PI-Pike

Hai , i want to do output short circuit test with full load . can i short the output directly with out any protection. otherwise need to connection any protection ? if i short the output with full load does my circuit will effect? And also i want to do reverse polarity test . To do this tests what precautions have to take. pls suggest me

Thanks for your replays i increased the bias winding turns. i took supply from secondary bias output to connect fan now its working fine

Hai ,
i want to connect led indicator. like charger on and battery full indicator .can you pls tell me how to connect this indicator circuit.

Hi pavan.kumar,

Hai , i want to do output short circuit test with full load . can i short the output directly with out any protection. otherwise need to connection any protection ?

- TopSwitch has an output short circuit protection. So you can short it directly.

if i short the output with full load does my circuit will effect?

- It will auto-restart.

And also i want to do reverse polarity test . To do this tests what precautions have to take. pls suggest me

- can you please tell me how this test is done?

Hai ,
i want to connect led indicator. like charger on and battery full indicator .can you pls tell me how to connect this indicator circuit.

- Connect the circuit on the output side

Regards,
PI-Pike