Uni SMPS 300W
- Thread starter Acca
- Start date
When voltage is low then duty cycle increases and then all so current increase , can you try up frequency ?
Same problems can be with core , because sometimes core on sample with 50 kHz can not give enough power , but if frequency go up to 75 kHz then work fine .
But like I m say my knowledge for smps is very low .
Same problems can be with core , because sometimes core on sample with 50 kHz can not give enough power , but if frequency go up to 75 kHz then work fine .
But like I m say my knowledge for smps is very low .
Hello people. I'm back.
I stopped worrying about the sound it makes when turning off.
So, there is only one last think that is bothering me.
Even using 8 (eight), YES, EIGHT diodes UF5408, that are for 3 amps each, on the output, they get really hot (can't put my finger for more than a second) with a load of 3 amps.
Nothing has burnt yet, but I'd like to know if someone has faced it.
Annnd, as I promised, the layout I made. There's an optional regulated 12+12 output.
I stopped worrying about the sound it makes when turning off.
So, there is only one last think that is bothering me.
Even using 8 (eight), YES, EIGHT diodes UF5408, that are for 3 amps each, on the output, they get really hot (can't put my finger for more than a second) with a load of 3 amps.
Nothing has burnt yet, but I'd like to know if someone has faced it.
Annnd, as I promised, the layout I made. There's an optional regulated 12+12 output.
sakisalfista
New member
Measure all diodes. If they are ok . But if I am not mistaken your secondary main caps are mounted with wrong polarity!
The diodes are ok, I assembled many already. It's something to do with the reverse voltage before the inductor.
The polarity of the capacitors are meant to be inverted, so it's easier to wound the inductor, enter on one side and gets out in the another, like an X.
sakisalfista
New member
Then just take the output just after the diodes and use a lamp as load and add one by one the other elements . Inductor capacitor resistors etc. in the air until you find the component that causes the overheating . The fact that you are not using a snubber circuit after the trafo output might explain an overvoltage spike from switching transistors but I don't think that it could heat the diodes that much if not at all.
Acca and all,
If I use double stack EI33 for the output traffo, is the no ot turns still the same per original schematic? (first post). I'm thinking of squeezing roughly 600w and by using TV Horizontal output transistor (TO-247).
Secondly, increasing the output voltage would mean disassembling the original core to add more turns to the secondary winding, am I correct?
Regards,
Albert
If I use double stack EI33 for the output traffo, is the no ot turns still the same per original schematic? (first post). I'm thinking of squeezing roughly 600w and by using TV Horizontal output transistor (TO-247).
Secondly, increasing the output voltage would mean disassembling the original core to add more turns to the secondary winding, am I correct?
Regards,
Albert
Silvio
Well-known member
If you stack a couple of cores then your trafo becomes bigger and need less number of turns for the primary (volts per turn will be larger) If for example you have one EI 33 core which have 50 turns for the primary then for a couple this number will reduce nearly by half. Do not just half the number as then you have to work out the Cross sectional area (csa) of both trafo stacked together and a new calculation has to be made according to the frequency of operation and the new csa of the trafo. The copper wire csa has to be suited to the new current handling in the primary and secondary current. The secondary turns will be calculated according to the new number of turns in the primary and taken proportionally according to the volts per turn.
For all this you have to disassemble both trafos make a new bobbin to suit the new size and yes you have to rewind it.
Regards Silvio
I am in the process of building Acca's fet version. Anyone out there can help with the details of the gate drive traffo.
I have read somewhere using EE16/19 winding for primary is 3x28 and for the sec 9t x2.
What does 3x28 means? is it winded 28t in 3 layer or is it 3 strands of wire winded in 28t ?
Also I tried using a torus (green color) winded 12t primary and 12t for the 2 secondaries (per schematic). It did not work, do I need to connect first the 3t feedback winding at power on test? I am using 100w bulb as load, nothing happened so far, main filter cap voltage is too low I am measuring about 100dcv.
Panos how did you managed to make it to work., I've seen your version, I need your help here.
Thank you!
Albert
I have read somewhere using EE16/19 winding for primary is 3x28 and for the sec 9t x2.
What does 3x28 means? is it winded 28t in 3 layer or is it 3 strands of wire winded in 28t ?
Also I tried using a torus (green color) winded 12t primary and 12t for the 2 secondaries (per schematic). It did not work, do I need to connect first the 3t feedback winding at power on test? I am using 100w bulb as load, nothing happened so far, main filter cap voltage is too low I am measuring about 100dcv.
Panos how did you managed to make it to work., I've seen your version, I need your help here.
Thank you!
Albert
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Silvio
Well-known member
Hello Albert, If I am not mistaken the gate drive trafo has not been touched and it is one pulled out of an ATX power supply. You only have to play with the feedback winding on the main trafo it could be 2 or 3 turns just check it out on the tread. Try to reverse the polarity from the feedback going to the gate drive. Recently someone was playing with the same circuit and found that R2 was getting hot. it could be that a lot of voltage drop is present on it but this value has to be found out by trial and error as gate transformers vary a little from one another. See that you have adequate voltage around 10v-15v supplying the gates during operation.
Good luck Silvio
Good luck Silvio
Silvio
While awaiting for a donor ATX so I can get an original EE19 core, I played with a 10mm mint green torus found on PC ******boards. Powering it up I got readings at the gates +/- 7 volts respectively it seemed to be too low to turn on the fets. I am using IRF730 for a test..3t of feedback winding in an ETD49 core. Any hint for possible adjustment to be made in order to get about 10-15v on the secondary of gdt? Still 12t all for primary and secondary bifillar winding, primary in between two secondaries.
Albert
Silvio
Well-known member
Hello Albert, An ETD 49 is rather a large transformer, and a lot of power can be absorbed from it. At 40Khz you can get 700-900 watts. I do not know if you know the number of turns you have in the primary of the etd49 or you just found it ready made.
I will make some assumptions for you but these may vary as I do not know yet the number of turns in the primary of the etd49
Let us assume you have 20 turns in the primary winding and the switching frequency is 45Khz. The topology used in the circuit is half bridge so half the mains voltage is arriving at the primary winding. The rectified and smoothed voltage is around 310vdc and we will have half of it so we have around 155v.
The turns per volt is 155v / 20 turns = 7.75v per turn. So every turn in the trafo is carrying 7.75v.
I am doing this to calculate the feedback winding voltage. So more or less you will be needing more or less 2 turns in the feedback to get 15.5v
Now we come back to the gate transformer. This is rather a small ferrite ring that you are using and somehow the turns ratio in the trafo will be more as this has a much smaller cross sectional area. However we can use a little less but we have to be careful as there will be a lot of current in it. This is why we use the resistor is series to limit the current.
I do not know what ring are you using but let us say you use 30 turns to carry this voltage. So your ring will have 3 wires in parallel twisted together first then you wind 30 turns with them on the ring. Use different colors for the wires so that you don't mix them up. You will take one wire for the primary. and the other 2 for the gates one for each fet.
Be careful as one of the secondaries must have a different phase according to the other secondary wire. Put a series resistor with the primary of the feedback winding to limit current going to the gate drive trafo as shown it the schematic. Start with a 100 ohm first and see what you get. You can gradually decrease until you have enough voltage at the gates with minimum current.
I hope you understood well. You can experiment with different number of turns in feedback winding say you can try 3 but this will add another 7v to your voltage and hence you will be needing a larger resistor. There is not much room to play with turns as the volt per turn is rather high on the main trafo.
You can also use enameled copper wire of say 0.2mm to wind your gate trafo but be careful as you have a high voltage difference between the high side fet and ground. if the windings tend to short with one another BOOM. See if you can find some kind of telephone wire which is thin and has insulation on it. If 30 turns do not fit in the ring that you have try with less turns. These are only assumptions and 30 turns may be too much.
Make some reserch about gating transformers maybe you can find information how to make them and what material (wire) is suited best for them.
Good Luck in your experiments and please be careful when playing with grid voltage.
Regards Silvio
I will make some assumptions for you but these may vary as I do not know yet the number of turns in the primary of the etd49
Let us assume you have 20 turns in the primary winding and the switching frequency is 45Khz. The topology used in the circuit is half bridge so half the mains voltage is arriving at the primary winding. The rectified and smoothed voltage is around 310vdc and we will have half of it so we have around 155v.
The turns per volt is 155v / 20 turns = 7.75v per turn. So every turn in the trafo is carrying 7.75v.
I am doing this to calculate the feedback winding voltage. So more or less you will be needing more or less 2 turns in the feedback to get 15.5v
Now we come back to the gate transformer. This is rather a small ferrite ring that you are using and somehow the turns ratio in the trafo will be more as this has a much smaller cross sectional area. However we can use a little less but we have to be careful as there will be a lot of current in it. This is why we use the resistor is series to limit the current.
I do not know what ring are you using but let us say you use 30 turns to carry this voltage. So your ring will have 3 wires in parallel twisted together first then you wind 30 turns with them on the ring. Use different colors for the wires so that you don't mix them up. You will take one wire for the primary. and the other 2 for the gates one for each fet.
Be careful as one of the secondaries must have a different phase according to the other secondary wire. Put a series resistor with the primary of the feedback winding to limit current going to the gate drive trafo as shown it the schematic. Start with a 100 ohm first and see what you get. You can gradually decrease until you have enough voltage at the gates with minimum current.
I hope you understood well. You can experiment with different number of turns in feedback winding say you can try 3 but this will add another 7v to your voltage and hence you will be needing a larger resistor. There is not much room to play with turns as the volt per turn is rather high on the main trafo.
You can also use enameled copper wire of say 0.2mm to wind your gate trafo but be careful as you have a high voltage difference between the high side fet and ground. if the windings tend to short with one another BOOM. See if you can find some kind of telephone wire which is thin and has insulation on it. If 30 turns do not fit in the ring that you have try with less turns. These are only assumptions and 30 turns may be too much.
Make some reserch about gating transformers maybe you can find information how to make them and what material (wire) is suited best for them.
Good Luck in your experiments and please be careful when playing with grid voltage.
Regards Silvio
Hi Silvio,
As always your input is substantial,
The pcb design I'm using is a similar topology with Acca's fet version, it was however designed to drive IRFP460. I do not have these fets yet (they come rare and expensive here in my place). I adapted/converted the design using Acca's so I can use any power fets I can find from discarded boards. ETD49 core I am using had 22t primary and 7tx2 centertap for the sec. self winded. I'd like to show some pics of my work but my internet access is too slow I get connection drops while attempting to upload images. By the way I am using AC mains bulb limiter as a safety precaution.
Regards,
Albert
Silvio
Well-known member
Hi Albert, What diameter is your gate drive torroid transformer? What number of turns are you using on it?
I will check on the net what AL value your torroid has and we can make up the number of turns needed for it. I am still at work but I will take a look tonight when I get home.
Ps Nice work you done with the PCB and placement of components. I cannot see the current limiting PTC thermistor in the input after the fuse. please try to find one and fit it in series with the supply rail. Without it the inrush current charging the primary bulk caps will blow your rectifier bridge at start up when you connect it directly to the mains.
Regards Silvio
I will check on the net what AL value your torroid has and we can make up the number of turns needed for it. I am still at work but I will take a look tonight when I get home.
Ps Nice work you done with the PCB and placement of components. I cannot see the current limiting PTC thermistor in the input after the fuse. please try to find one and fit it in series with the supply rail. Without it the inrush current charging the primary bulk caps will blow your rectifier bridge at start up when you connect it directly to the mains.
Regards Silvio
