From my point of view many things are wrong. For example: pin 2 depends on pin1, but no info about pin1. Pin4 waveform timescale is set differently in a way neither the details nor the period can be seen. Knowing freq. would be quite helpful generally.
When you said the IC heated up I assumed you replaced it after... Yes, it could be damaged.
And I had many questions and advices unresponded.
When you said the IC heated up I assumed you replaced it after... Yes, it could be damaged.
And I had many questions and advices unresponded.
I apologize by my insistence, but most Motorola IC's are very problematic. This is a good example. Other is MC3x063, very faulty IC which in the best case stops working, but often becomes short circuited between input and output, an in a buck topology this may be catastrophic. Other example is MC384x, which they don't work at all, also being new. An extra word is for the 78S40. I saw various of them who catch fire in normal circumstances.
Once again, I suggest to change of PFC controller for one of the ST line, that are by far, best circuits.
I speak (Write) from repairing point of view, not from the designer one.
Osvaldo.
Once again, I suggest to change of PFC controller for one of the ST line, that are by far, best circuits.
I speak (Write) from repairing point of view, not from the designer one.
Osvaldo.
Pin 1 has about 1.85V on it that comes from the 300V output voltage. I will replace the IC and probe everything again with a better timescale, thanks 🙂
I didn't but I will now, my bad!!
I already orderer some L4981 just in case but they will take some time to get to my location so meanwhile I want to try to get this working 🙂
Ok, I soldered a new IC. When I plugged in everything the fuse and MOSFET blown up. So I replaced the fuse, MOSFET and put back the 1mH inductor instead of the 250uH I had, I put a 75K load and connected the PFC through an incandescent lamp to the line to protect it from short-circuits/large currents.
Now, the IC seems to switch some pulses every once some seconds, like a switching burst every 10 seconds and sometimes even more. Every time it switches there is a large input current which shouldn't be normal as the load is only 75K but the output voltage does go to 400V.
The problem I see now is this:
This is the ouput from the AC rectifier, it has a DC offset! I don't even know how this is possible. This is the line input as expected:
I even desoldered the bridge rectifier and just measured directly with the scope and still can see the DC offset!
I'm not taking something in account, I'm sure I am but I just don't know what! I changed the rectifier just in case and it's the same. I don't think the scope is the problem.
Right know I will have to slow down the development of this due to my work but will keep trying to make it work, just in case I don't write everyday! Thank you all for your help!
Now, the IC seems to switch some pulses every once some seconds, like a switching burst every 10 seconds and sometimes even more. Every time it switches there is a large input current which shouldn't be normal as the load is only 75K but the output voltage does go to 400V.
The problem I see now is this:
This is the ouput from the AC rectifier, it has a DC offset! I don't even know how this is possible. This is the line input as expected:
I even desoldered the bridge rectifier and just measured directly with the scope and still can see the DC offset!
I'm not taking something in account, I'm sure I am but I just don't know what! I changed the rectifier just in case and it's the same. I don't think the scope is the problem.
Right know I will have to slow down the development of this due to my work but will keep trying to make it work, just in case I don't write everyday! Thank you all for your help!
The "offset" is normal. You charge a small capacitor, its charge doesnt go to 0 until the next zero crossing.
The small capacitor is the scope input capacitance? Because when I read this voltage in the IC pin 3 it also has this offset. It doesn't goes to 0 and it should AFAIK.
The small capacitor is the scope input capacitance?
No. There is a capacitor in your circuit. Look at the sch! But when only scope is attached, then you introduce hidden/parasitic capacitances.
It doesn't go to 0 because PFC doesn't work. As soon as PFC starts to work continuously (with load on output) the voltage after rectifier will follow absolute sine wave.
With only a scope probe on rectifier the capacitance is much lower, but also the load current is lower.
No. There is a capacitor in your circuit. Look at the sch! But when only scope is attached, then you introduce hidden/parasitic capacitances.
It doesn't go to 0 because PFC doesn't work. As soon as PFC starts to work continuously (with load on output) the voltage after rectifier will follow absolute sine wave.
With only a scope probe on rectifier the capacitance is much lower, but also the load current is lower.
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It seems to be switching now, I even get voltage on pin 2 which I wasn't having before. I do unwind some turns on the secondary side and I'm getting about 12V Vcc and I'm thinking that maybe it's firing the UVLO, I will try to power the IC from an external power supply to discard that.
I´m not an SMPS guy , so "I'm looking from outside" ... which sometimes is good because I *assume* nothing, just look at everything and try to analyze , so I have a few questions nobody asked (we are already on page *eight* , 72 posts with an unsolved problem) so please dissipate my doubts:
1) you are trying to get 400V dc ... what are you trying to power with that?
I have seen no statement or power or current.
2) do you know that as is that supply will KILL you?
There is no galvanic separation between mains and load, everything there is mains LIVE and DEADLY.
You are not using a switching transformer (which would have galvanically separated windings) but a simple step up inductor, with continuity between both halves of the circuit (original voltage and load).
3) *what* are you trying to convert into 400V DC?
You are stating with a horrible , full wave rectified AC waveform, obviously changing all he time at unfiltered 100Hz frequency .
You should start with raw but reasonable about 300V DC and only then do all the switching and conversion.
Where is the mains side reservoir capacitor?
I mean something around 100 or 200uF, absolutely minimum 47uF , always at least 350 or 400V DC.
You only have a ludicrous 100nF cap (Cin 1) which of course is useless for that.
Since you are starting with unfiltered mains rectified AC, you will have same waveform at the load side, and only then you charge a filter cap.
This circuits resembles more the crude converters used in CFL lamps or "12V electronic transformers" used to power 12V small quartz lamps han a proper DC supply.
Of course, in lamps horrible ripple does not matter, mains frequency was chosen high enough so our eyes can not detect flicker.
4) I do not know how is your Lab equipment connected and grounded, remember b-you are connected to a live circuit, you can either damage it or worse, be shockd/killed by touching a seemingly safe piece of equipment, far away from the "dangerous area" .
Ok, please answer these doubts posted above.
I´d love to hear my concerns are unjustified, that you are powering this from a floating secondary 220-220 isolation transformer which is the safe way to work with the primary side of SMPS (which in this case is ALL of the supply because of lack of internal isolation).
In fact, I think I should report this thread to DIYA Moderators, since it´s a discussion on improperly insulated and ungrounded LIVE VOLTAGE circuits.
1) you are trying to get 400V dc ... what are you trying to power with that?
I have seen no statement or power or current.
2) do you know that as is that supply will KILL you?
There is no galvanic separation between mains and load, everything there is mains LIVE and DEADLY.
You are not using a switching transformer (which would have galvanically separated windings) but a simple step up inductor, with continuity between both halves of the circuit (original voltage and load).
3) *what* are you trying to convert into 400V DC?
You are stating with a horrible , full wave rectified AC waveform, obviously changing all he time at unfiltered 100Hz frequency .
You should start with raw but reasonable about 300V DC and only then do all the switching and conversion.
Where is the mains side reservoir capacitor?
I mean something around 100 or 200uF, absolutely minimum 47uF , always at least 350 or 400V DC.
You only have a ludicrous 100nF cap (Cin 1) which of course is useless for that.
Since you are starting with unfiltered mains rectified AC, you will have same waveform at the load side, and only then you charge a filter cap.
This circuits resembles more the crude converters used in CFL lamps or "12V electronic transformers" used to power 12V small quartz lamps han a proper DC supply.
Of course, in lamps horrible ripple does not matter, mains frequency was chosen high enough so our eyes can not detect flicker.
4) I do not know how is your Lab equipment connected and grounded, remember b-you are connected to a live circuit, you can either damage it or worse, be shockd/killed by touching a seemingly safe piece of equipment, far away from the "dangerous area" .
Ok, please answer these doubts posted above.
I´d love to hear my concerns are unjustified, that you are powering this from a floating secondary 220-220 isolation transformer which is the safe way to work with the primary side of SMPS (which in this case is ALL of the supply because of lack of internal isolation).
In fact, I think I should report this thread to DIYA Moderators, since it´s a discussion on improperly insulated and ungrounded LIVE VOLTAGE circuits.
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