I know, working with PICs for almost 20 years, but that does not matter …
What is important for me is at least in those power converter application, I will not allow that price difference of some components influence my design decisions because we operate with most critical part usually of more complex machines and do not want to think about safety because few $ and get in question someone's life …
I come from industry fields and know very well what safety means, that is not something to makes compromises! Safety is on first place!
When you get in situations like lose of neutral power wire/line and get destroyed almost all devices involved in automation of some machine (not designed/implemented by us) and only pice left over is our PLC which we put there, you will get the point why not to makes compromises
I always prefers quality and robustness over price. Who don't like my price, find someone else to do the job … and in many cases customers back to me after catastrophic events they experienced with some cheap implementation.
What is important for me is at least in those power converter application, I will not allow that price difference of some components influence my design decisions because we operate with most critical part usually of more complex machines and do not want to think about safety because few $ and get in question someone's life …
I come from industry fields and know very well what safety means, that is not something to makes compromises! Safety is on first place!
When you get in situations like lose of neutral power wire/line and get destroyed almost all devices involved in automation of some machine (not designed/implemented by us) and only pice left over is our PLC which we put there, you will get the point why not to makes compromises
I always prefers quality and robustness over price. Who don't like my price, find someone else to do the job … and in many cases customers back to me after catastrophic events they experienced with some cheap implementation.
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In any LLC converter, the most critical parameters are minimum and maximum working frequency (operating range) and to get that information we need to know Ls/Lm on particular inductor / transformer which we will use.
To do non destructive test of integrated on non integrated transformer in environment near real operating environment on productive board, it is useful to do tests with setup similar to one as shown in attached file.
You need to find maximum amplitude on resonant capacitor in case of short and open secondary windings, sweep frequency manually and readout frequency at maximum amplitude. Via Thomson's equation you can calculate quite accurately Lm and Ls.
Also you will know minimum operating frequency and for example it is safe to set final design to 10-15kHz above that minimum as a starting point.
Setup require two supplies, 10V must be 1A current limited.
Also you can test with equivalent Rac (put standard resistor) on secondary to get more details on transformer behaviors.
To do non destructive test of integrated on non integrated transformer in environment near real operating environment on productive board, it is useful to do tests with setup similar to one as shown in attached file.
You need to find maximum amplitude on resonant capacitor in case of short and open secondary windings, sweep frequency manually and readout frequency at maximum amplitude. Via Thomson's equation you can calculate quite accurately Lm and Ls.
Also you will know minimum operating frequency and for example it is safe to set final design to 10-15kHz above that minimum as a starting point.
Setup require two supplies, 10V must be 1A current limited.
Also you can test with equivalent Rac (put standard resistor) on secondary to get more details on transformer behaviors.
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Or something like this for some high voltage application (kind of combined serial/parallel resonant converter), transformer is in box filled with petroleum for high voltage isolation …
Last photo is resonant capacitor with current transformer, just to get a picture about power of this converter
This design/approach is already tested and work in some industrial application in very harsh environment without any problems for many years ...
Yu3ma, those u-core transformers are cool. But there is no closed magnetic loop, ie external u leg ?
I have some big a-s ferrite toroids , was thinking about trying to build a resonant converter feeding a teslacoil in honour of the great inventor, typically series-parallell topology but that is a different story.
Oh, about the winding. Using split bobbin means using litz due to proximity effect in multilayers.
Using concentric windings , interleaved , separated by a large radial spacer, ie extra turns of insulating tape brings down stray capacitiance and pulls up leakage quite a lot. Advantage is you can use ordinary magnetic wire. Penalty is worse thermal properities and you might end up with a larger core to fit your windings in available window, not so cost effective in production of course.
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Hi all,
I have modified the circuit to make it work.
The problem was that due to the huge capacitance at the output the PWM IC could not self supply from the transformer aux winding and thus it continuously
restarted until the output voltage was high enough.
I have added another winding on the resonant choke so that when the output voltage is low (capacitors discharged) there is practically all the PFC voltage across the resonant inductor, the added winding on Lr in used to supply the PWM IC during start up.
Now the start up is smooth but probably the soft start is a little bit too fast and
sometimes the PFC goes in current limitation due to excessive power demand from the LLC stage. To limit the damages in case of something goes wrong I have replaced my bulk cap with a 68uF/450V one instead of a 680uF... probably this has also something to do with the PFC current limitation during start-up. I would like to be more sure about my LLC operation before putting 680uF and see whats happens....
I have set the switching frequency at slightly above 100kHz and I reach 115Vdc at the output at no load (as I was expecting). The problem is that at no load or at very low load the primary FETs are completely in hard switching due to the lack of circulating current to discharge their Coss.
I think I need to gap my transformer to add some magnetizing current to be able to be in ZVS at no load and transform this stuff in a real LLC converter.
I have no heatsinks now on my FETs but I have pulled anyway around 500W for some seconds, current and voltage waveforms seems ok at high load and the PFC voltage stays correctly regulated at 390V.
The FETs seems to heat up more at no load rather than at 500W... probably due to ZVS loss
I have modified the circuit to make it work.
The problem was that due to the huge capacitance at the output the PWM IC could not self supply from the transformer aux winding and thus it continuously
restarted until the output voltage was high enough.
I have added another winding on the resonant choke so that when the output voltage is low (capacitors discharged) there is practically all the PFC voltage across the resonant inductor, the added winding on Lr in used to supply the PWM IC during start up.
Now the start up is smooth but probably the soft start is a little bit too fast and
sometimes the PFC goes in current limitation due to excessive power demand from the LLC stage. To limit the damages in case of something goes wrong I have replaced my bulk cap with a 68uF/450V one instead of a 680uF... probably this has also something to do with the PFC current limitation during start-up. I would like to be more sure about my LLC operation before putting 680uF and see whats happens....
I have set the switching frequency at slightly above 100kHz and I reach 115Vdc at the output at no load (as I was expecting). The problem is that at no load or at very low load the primary FETs are completely in hard switching due to the lack of circulating current to discharge their Coss.
I think I need to gap my transformer to add some magnetizing current to be able to be in ZVS at no load and transform this stuff in a real LLC converter.
I have no heatsinks now on my FETs but I have pulled anyway around 500W for some seconds, current and voltage waveforms seems ok at high load and the PFC voltage stays correctly regulated at 390V.
The FETs seems to heat up more at no load rather than at 500W... probably due to ZVS loss
Hi there
Has someone this model here for download? I am busy with a resonant for the hybrid amp/circlotron. 320 volts, 6.3 and 12.6 volts regulated and 2 x 120 volts,high voltages are mA for tube supply.
Thanks in advance
I found that using a sig gen in series with resistor and resonant tank I found the resonant frequency.
I then added a few percent to that frequency for power on frequency.
I added about 200% for none power on frequency.
I got a PIC micro to produce those frequencies depending on feedback signal.
Worked a treat.
You mean this kind of finding resonance?
this systems are quite complicated, but interesting. I did try with low load and high load and feedback, a Q of 0,3 and Lm 6 did work, calculated from a sheet, I can not post here to big.
I did read also about asymetric pwm resonant, these do even better with width load systems, like audio amps and tv.
regards
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