SMPS using TOP244p
Hello, i am working on an SMPS ckt with multiple outputs 12V 15V and 24V. the total power is 19W and i m using top244p. 12V is fon Fan , 24V is for relay and 15V is for op-amp and mosfet drain which is then connected to pulse transformer to drive the main IGBT. i m using simple zenner diode feed back for 15V winding. The problem what i am facing is the power supply is not able to start. i went through the troubleshoot guide givrn in apllication note and checked all the points. There is no issue in layout or even in clamp zenner.
What could be possible reason for not starting the power supply.
I would deeply appretiate the help. Please find attached image of ckt diagram.
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Transformer was designed by me only, It was designed using PIXls Designer 8. i checkd it and it is functioning properly. The control pin is getting charged to 5.7V and its holding the charge for around 10ms and the discharging again to 4.7V since there is no current sensed by the control pin. what i am seeing at the drain or across the primary winding is the pulse of very short duration. what i think is the MOSFET inside topswitch is trying to turn on but its actually not turning on properly and this happens at around 80V-85V ac input and continues till 230V ac. I am attaching an o/p voltage as well as the transformer design document for the refrerence. The o/p voltage (15V) what you are seeing the peak pulse is repeated every after 1sec, meaning is the relay tries to start every after 1 sec. The avg. voltage it shows is 10V only. what i assume is since the o/p volltage is not going beyond 13V the zenner is not functioning and because of that the opto is not turning ON and hence there is no current transfer to bias winding. the bias winding is designed for 15V only. is there any thumb rule or design eqn. for bias voltage? because i did not find it (the formula or how to decide the bias voltage) on any of your design document.
We have not used the stacked windings for transformer. we have each winding seperate. the 12V winding do not share the common signal ground. it is isolated and used for fan application. This is basically an auxilarry supply unit for 200A welding machine. and hence the i/p capacitor is of high value (3* 680uf/450V_electrolytic). but the high value of iput capacitor should not affect the performance.
Is top244p good enough for this application as i told the maximum power rating of this APU is 19W.
the power supply is going in auto restart mode. Control pin capacitor charges and discharges continuously as well as the auto restart frequency is 1Hz as per the datasheet, but i am not able to understand why it is going into auto-restart mode. the o/p are not shorted, i have connected dummy load across each o/p capacitor.
if you see the image of the o/p voltage, there is a spike at the starting , that spike is supressed by 150 ohm resistor and hence i am getting avg. voltage as 10V. not enough to turn on zener and hence the min. Icd of 2mA can not be achieved and hence the TOP is in auto-restart mode. How to increase that current because if i reduce the value of resistor further , if the ckt gets functional it will inject more current in the control pin. PLZ suggest...
Looks like your feedback loop is somewhere broken. Check for continuity from +15V to 150 ohms resistor to opto diode to zener to GND
Connect a DC source (let say 12 volts) to the collector of the opto coupler. The connection should be through a diode (+12VDC to anode of a diode, Cathode to the collector, 12V_Return to primary retun) Turn on your +12 VDC, then power up the power supply and see if it goes into regulation.
For what you are describing, your feedback loop si open.
the o/p is not going into regulation even after connecting the 12V dc source to the anode of diode. it gives me the same type of voltage waveform at the o/p of 15V (image of which i had shared earlier)
Check the face of your transformer . Make sure each winding is in the correct phase as indicated in the schematic.
Check your feedback componets. Your feedback compenents may be different that in the schematic, so your controller may not getting feedback.
All components are same. According to design of transformer, the inductance of primary winding should be 895 uH, if i put a current probe in +Vdc and primary winding i have high switching current pulses at the time when the MOSFET tries to turn ON. the Peak current according to design should be 0.6A but that peak is going beyond 0.6A. i didnot assemble the transformer ,i just designed it, and was given to outside vender so is there any way this could trigger the TOPswitch in auto restart mode? if yes what can i do to prevent the same.?
Did you check the phase of your transformer as I asked you in the last reply?
Did you check the feedback brack to make sure it is closed?
Yes i checked that, the connections are correct and the feedback loop is not broken, however this low inductance of primary, can it cause the current spike which is triggering the top switch in auto restart mode, because this is one of the reason mentioned in your application note that high switching current may trigger the topswitch into auto restart mode. Do i have to increase the number of turns of primary and secondary accordingly by keeping the turns ratio constant.
The transformer design needs to be reviewed to see if it is capable to deliver full power.
We do not know if just increasing the number of turns will work because other things need to be consider.
I recommend you to download PI expert software from the below link. Then, enter your parameter into the PIXLS software.
Enter number of turns on each winding, Input voltage, efficiency (about 83 %) Adjust your total output power to match primary inductance.
Check for flux density to be not more than 3000 gauss. This analysis will tell us if your transformer is the cause of the problem
Let me know what are the result you are obtaining
Regards
http://www.powerint.com/en/design-support/pi-expert-design-software
Hi Abhishek,
You should better put a rethought on the transformer Bmax & Current Capacity.
May be a better Ferrite will help you.
I have some questions for you.
Who designed the transformer? Can you please post your transformer design document?
When you said the power supply does not start up, you mean you do not see any activity in the DRAIN node when you apply input voltage?
I think the circuit needs to be simplified to find the problem.
Connect the V pin of the controller to SOURCE pin (or primary return ). This will disable the input voltage sensing circuit. Remove the output load. Start your power supply from zero V and gradually increase VIN. You should be able to see the some activity at the DRAIN node and have output voltage. The output should be able to regulate at very low VIN. Check your voltage of the control pin. The internal current source should change the control pin capacitor to about 5.8V then then the controller should start running.