Thank you very much. This is the most clear explanation I have seen on this subject, especially the last parts about the voltage ratings of parts, and the capacitive coupling of EMI through an isolation transformer. I have often wondered why modern oscilloscopes are not designed for isolation in the first place. Oscilloscopes have been built without any exterior metal for well over a decade. It seems to me that the standard practice of an earth reference is just an attempt at selling me overpriced differential probes. Now I must go watch your latest upload on differential probes to further isolate my ignorance. Thanks for the upload. -Jake
Hi, firstly thank you very much for publishing these videos. I am enjoying them very much . You addressed the issue of floating the scope but not the practice of floating the DUT (the convertor being tested) in my experience this is the most common solution and I wondered what issues this could pose other than the isolation transformer must sometimes be very large and expensive?
Thanks for the nice video on Oscilloscope... If there is any practical related to above discussion like effect due to ground voltage/current, effect due to flux during high frequency. Can we create artificial EMI and see the effect through oscilloscope. Regards
Digital multi channel scopes can compare two signals, so channel 1 would be the gate and channel 2 the source (of the high side switch), and the ground clips are disconnected. The resolution and speed are poor, but at least you can do the measurement. I also thought about isolating the converter itself and not connecting the scope to the mains earth.
Hi sir, can you please address my queries 1.power ground and analog ground should be common or different. 2. In a 3 phase inverter fed motor drive when using more than 48 volt battery why it is required to use isolated gate driver. 3. I have seen spike in current wave form and the mosfet failed when i used to probe vgs and vds .i am using isolated scope yokogawa dl850ev.what may be the possible reason . Thanks in advanve
You show wrapping the ground wire around the probe which is not desirable since that makes an inductor! I was taught to just hold the wire against the probe. I wonder why there aren't more scopes that are double insulated and therefore do not need a ground. As well as battery operated scopes that are basically ideal for floating measurements, especially for signals too small for a differential probe to resolve.
Thanks for good comments. Wrapping a bare wire on metal does not make a coil if tied. Differential probed are not that expensive anymore (save the high end) and they provide a very good solution for power electronics. For very low signal, true differential scope are around (e.g. Picoscope 4000 , if I remember right the number. I do own one).
Just realized that when referring to wrapping you meant the first mode I showed in video, wrapping of the isolated ground wire. You are right, but holding the wire against he probe is rather cumbersome. Thanks again for comment.
Since you broight up the common mode problem, I have a question related to it. Isolated converters have a Y cap across the transformer to mittigate common mode problems. However, I could not found any relevant documentation on the subject on how to select such cap. It seems to me that it is trial and error ? Could you give your view on this ? Thanks.
Probably this has been solved by now, it's a question I was trying to answer myself recently. My thoughts is that you'd want to use the largest Y cap value possible (less impedance for CM noise to filter better), while adhering to leakage current regulations. Let me know if there's some more thorough guidance I can check for this.
Sam, I sincerely hope you never stop this power electronics series. Best of luck and thank you.
😊👍
Thank you very much. This is the most clear explanation I have seen on this subject, especially the last parts about the voltage ratings of parts, and the capacitive coupling of EMI through an isolation transformer.
I have often wondered why modern oscilloscopes are not designed for isolation in the first place. Oscilloscopes have been built without any exterior metal for well over a decade. It seems to me that the standard practice of an earth reference is just an attempt at selling me overpriced differential probes.
Now I must go watch your latest upload on differential probes to further isolate my ignorance.
Thanks for the upload.
-Jake
😊Thanks
Hi, firstly thank you very much for publishing these videos. I am enjoying them very much . You addressed the issue of floating the scope but not the practice of floating the DUT (the convertor being tested) in my experience this is the most common solution and I wondered what issues this could pose other than the isolation transformer must sometimes be very large and expensive?
Thank you very much for these videos!
Thanks for comment
Thanks for the nice video on Oscilloscope... If there is any practical related to above discussion like effect due to ground voltage/current, effect due to flux during high frequency. Can we create artificial EMI and see the effect through oscilloscope. Regards
In any PCB that includes both power and signals you can clearly see these effects.
thank you so much for these videos you are the best
👍😊
Please more basic courses in English. Great teaching thank you sir!
Thanks. Doing both.
Digital multi channel scopes can compare two signals, so channel 1 would be the gate and channel 2 the source (of the high side switch), and the ground clips are disconnected. The resolution and speed are poor, but at least you can do the measurement. I also thought about isolating the converter itself and not connecting the scope to the mains earth.
Ground clips need to be connected.
Hi sir, can you please address my queries
1.power ground and analog ground should be common or different.
2. In a 3 phase inverter fed motor drive when using more than 48 volt battery why it is required to use isolated gate driver.
3. I have seen spike in current wave form and the mosfet failed when i used to probe vgs and vds .i am using isolated scope yokogawa dl850ev.what may be the possible reason .
Thanks in advanve
1. Separated but them connected in one point.
2. The reason is high power
3. There are capacitive paths that can still nject noise.
You show wrapping the ground wire around the probe which is not desirable since that makes an inductor! I was taught to just hold the wire against the probe.
I wonder why there aren't more scopes that are double insulated and therefore do not need a ground. As well as battery operated scopes that are basically ideal for floating measurements, especially for signals too small for a differential probe to resolve.
Thanks for good comments. Wrapping a bare wire on metal does not make a coil if tied. Differential probed are not that expensive anymore (save the high end) and they provide a very good solution for power electronics. For very low signal, true differential scope are around (e.g. Picoscope 4000 , if I remember right the number. I do own one).
Just realized that when referring to wrapping you meant the first mode I showed in video, wrapping of the isolated ground wire. You are right, but holding the wire against he probe is rather cumbersome. Thanks again for comment.
Since you broight up the common mode problem, I have a question related to it. Isolated converters have a Y cap across the transformer to mittigate common mode problems. However, I could not found any relevant documentation on the subject on how to select such cap. It seems to me that it is trial and error ? Could you give your view on this ? Thanks.
Have a look at czcams.com/video/5NRiLOvmXdA/video.html it includes some relevant information. I do not recall any specific documentation on subject.
@@sambenyaakov thank you. Good information.
Probably this has been solved by now, it's a question I was trying to answer myself recently. My thoughts is that you'd want to use the largest Y cap value possible (less impedance for CM noise to filter better), while adhering to leakage current regulations. Let me know if there's some more thorough guidance I can check for this.
Does isolated channels oscillos (like FLUKE-190-104) do the trick with floating measurements?
Yes indeed. But notice they do not provide CMRR data.