bad premonitions

[Riss]

I soldered and experimented with this simple circuit ( VMOS , diode, capacitor, coil )- in typical PI mode - 150 microsec. pumping current into the coil , shutdown the VMOS , the capacitor reverses the current and after the energy in the coil is returned to the supply- then pause for ,, listening " about 1.2 milliseconds long . https://www.geotech1.com/forums/atta...3&d=1274443630 -Thread: Let's made a PC-base metal detector with usb interface !!!

( The principle and scheme is the same , as in the thread ,, PI metal detector with energy recuperation " from deemon (06-04-2012 )- circuit_4.gif- https://www.geotech1.com/forums/atta...1&d=1338765051 -section A-B-C-D- oscillogram of the current through the coil . I had my suspicions and they were confirmed -immediately after the discharge of the coil in the power supply damping oscillations occur with the resonant frequency of the coil ( 1,5 milihenries ) and capacitor to reverse the current ( 33nF ). I tried 3 types VMOS , even the bipolar MJE13007, 10nF capacitor (a drowning man grasps at a straw ) - there is no salvation from the damned damping oscillations ! I dropped everything - I have things from which I will receive money ...

[dbanner]

Air coil or ferrite core?

[Riss]

Air coil , of course...- a simple DD search head . Аbout 4.5 ohms resistance at 1.5 millihenries TX coil . I also tried with the monocoil around 0.6 millihenry .Тhe current waveform is seen with a 0.1 ohm resistor to ground . Аctually i made a huge mistake with the thread title - it was supposed to be something like ,, Тhe metaverse of computer simulations and PI reality on the oscilloscope screen". Тhe choice is yours to trust the computer simulations. Мy choice is to trust only the screen of my good old ANALOG oscilloscope ( I also have a small digital single beam oscilloscope , but practice has shown that he too often suffers from obsessive hallucinations and shows things that are not on the screen of the two-channel analog oscilloscope )

. Аfter experimenting with at least three coils , and with experiments with diodes and transistors from at least three different manufacturers . PI circuits can make any simulation software and programmer look like a monkey

[Tinkerer]

Air coil , of course...- a simple DD search head . Аbout 4.5 ohms resistance at 1.5 millihenries TX coil . I also tried with the monocoil around 0.6 millihenry .Тhe current waveform is seen with a 0.1 ohm resistor to ground . Аctually i made a huge mistake with the thread title - it was supposed to be something like ,, Тhe metaverse of computer simulations and PI reality on the oscilloscope screen". Тhe choice is yours to trust the computer simulations. Мy choice is to trust only the screen of my good old ANALOG oscilloscope ( I also have a small digital single beam oscilloscope , but practice has shown that he too often suffers from obsessive hallucinations and shows things that are not on the screen of the two-channel analog oscilloscope )

. Аfter experimenting with at least three coils , and with experiments with diodes and transistors from at least three different manufacturers . PI circuits can make any simulation software and programmer look like a monkey

Your circuit does not work because the timing is wrong.

[Riss]

Thank you very much, but the scheme ( circuit ) is as follows :
timer NE555 , after him - HEF4017 , from pin3 4017 - to CD4049 ( buffer ) who drives IRF740 in the source of which there is 0.1 ohm ,to which we attach the probe of the oscilloscope. Diode is BYW76 . That is all . There is no timing . Damping oscillations occur after almost all of the energy stored in the coil is returned back to the supply (as I suspected ) For experiments I use only capacitors, which are marked as MKP . I have an L and C meter .SRF of the first coil used for the test is about 210 Khz . Of course the observed damping oscillations are with a frequency at which the coil and capacitor resonate -1,5 mH and 33 nF for example . Circuit is the same as comment #819 , 05-21-2010, 03:07 PM , Thread: Let's made a PC-base metal detector with usb interface !!! , guru - Aziz . If you repeat the circuit you will see for yourself ( contemplate ) . The fly is released from vistac2000 and starts buzzing in the head of ...- you will see for yourself - he has too , too much posts on this thread . I am very grateful to this fly .

[dbanner]

Have a look at phase 4 enhanced, the mosfet is again switched on towards the end of the coil discharge, to compensate for losses. But this gate pulse appears to be of much shorter duration than the drive pulse. So there appears to be a timing scheme involving the gate logic. Maybe at this point, the oscillations you describe are precluded because the residual energy in the coil cannot flow into the buffer capacitor. For this to be plausible, the coil voltage supply would have to be disconnected through this phase. ????

It seems to me that there must be a timing scheme involving the gate logic and the coil supply.

[dbanner]

Damping oscillations occur after almost all of the energy stored in the coil is returned back to the supply (as I suspected ).

This is when Phase 4 enhanced is supposed to kick in( another shorter pulse at mosfet gate ), precluding any possibility of oscillations, because the buffer capacitor cannot charge, because the coil supply is simultaneously disconnected. The remaining energy in the coil now must return to the electrolytic caps.

Of course, I could just be imagining things, just a fallacy.

"Phase 4 enhanced" reference to Aziz post #819

[Riss]

Thanks, but I had read and understood what you were referring to , even before I make the circuit and measure the oscillations in question .I tried this trick but it doesn't help.The computer simulation is about the operation of this circuit in continuous mode - without pauses , and in this mode everything is ok . The problem hits us in the head when there is a pause - a classic in PI.pauses are full of fading oscillations I came to the conclusion that whatever we do , it is not possible to avoid these damn damping oscillations . They drove me to utter despair.

[dbanner]

A good way to avoid despair is to buy minelab detector. On the other hand, the hole left in the pocket may require some pharmacy medication, or a weekend retreat to the funny farm

[Riss]

Let's put good humor aside and use theoretical analysis using the method of short time segments . It becomes most interesting with the energy in the coil in the two time slices -just before the current through the coil becomes zero , and in the next segment .

[Tinkerer]

Let's put good humor aside and use theoretical analysis using the method of short time segments . It becomes most interesting with the energy in the coil in the two time slices -just before the current through the coil becomes zero , and in the next segment .

If it is possible for you to post a picture of the current wave form and the voltage wave form, we could analyze it here. Oscilloscope or simulation. And your actual circuit.

[Riss]

That would be great - exactly the computer simulation i wanted to see . I repeat from my first post here is a link to the circuit - Thread: Let's made a PC-base metal detector with usb interface !!! , page 33 , Laptop IB-PI Transmit Coil DriverPhase1.gif (10.6 KB, 1711 views) - ( #819 ) . The pulses to the gate IRF740 are 150 microsec. long , pauses - 1350 microsec. ( 9 x 150 ) . The first capacitor , which I tried was 33 nF . coil - 1,5 mH / 4,5 ohm. Power supply - 9 volts . The shape of the current through the coil is as here- File Type: gif Laptop IB-PI Transmit Coil DriverSignals.gif (42.4 KB, 1157 views) - (#821 , page33 ). Only in my case during pause time damping oscillations are observed with an initial amplitude about 1/30 of the second peak current . They have a small but noticeable amplitude even after 1350 microsec. It is . Now the ball is in the court of computer simulations...

[Tinkerer]

That would be great - exactly the computer simulation i wanted to see . I repeat from my first post here is a link to the circuit - Thread: Let's made a PC-base metal detector with usb interface !!! , page 33 , Laptop IB-PI Transmit Coil DriverPhase1.gif (10.6 KB, 1711 views) - ( #819 ) . The pulses to the gate IRF740 are 150 microsec. long , pauses - 1350 microsec. ( 9 x 150 ) . The first capacitor , which I tried was 33 nF . coil - 1,5 mH / 4,5 ohm. Power supply - 9 volts . The shape of the current through the coil is as here- File Type: gif Laptop IB-PI Transmit Coil DriverSignals.gif (42.4 KB, 1157 views) - (#821 , page33 ). Only in my case during pause time damping oscillations are observed with an initial amplitude about 1/30 of the second peak current . They have a small but noticeable amplitude even after 1350 microsec. It is . Now the ball is in the court of computer simulations...

As Aziz thanked me for the circuit, I feel obliged to give you some further explanations on how it works.

[Tinkerer]

Triangular

Screenshot of the simulation. This is correct.

How does your waveform compare with that?

[Riss]

My oscillogram : the current through the coil increases linearly of zero value to a maximum positive value for 150 microseconds , quarter sine to zero , another quarter sine to a maximum negative value (the current is slightly less - active losses ) , linear current reduction to zero for about 120 microseconds . Thanks for the link .Hadn't read it. This circuit has exactly the same principle of action and is the same as ,, PI metal detector with energy recuperation " from deemon (06-04-2012 ) - circuit_4.gif- https://www.geotech1.com/forums/atta...1&d=1338765051 - years ago I became familiar with the thread of deemon. The principle is easy to understand . It would have been nice to see a computer simulation of how the circuit works in Discontinious Mode . Precisely the current oscillogram in the discontinuous mode carries information about physical processes occurring in the coil (with its own capacity and active resistance) and the capacitor at the moments of time just before the current through the coil becomes zero , when the current is zero and in the next time slice .