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Author Topic: Controller No5 With Protection - Looking for Explosions  (Read 105873 times)

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Thanks Grump, looking into it.

Itsu
   

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I removed the both Pic's and used my dual channel FG to feed white noise (5Vpp, 1.5V offset) to the both MOSFET driver inputs via a 50 Ohm series resistor.

There seem to be some (thermal?) runaway condition happening as (with no drain voltage on the MOSFETs), gradually the current into the PCB (driver only) increases untill its that hot i can smell it.

Same when also putting on the drain voltage on the MOSFETs, gradually the current through the MOSFETs increase untill i stop it.

I think the circuit is missing some kind of MOSFET driver output / MOSFET gate clamping (10K to ground and / or zeners).

I will add that tomorrow to see if it stabilize it.

Itsu

I added a 1K resistor across gate/source of each MOSFET, but with direct white noise input into the both MOSFET driver inputs at a certain point i get again the runaway.

So i added again the high pass filters between the FG and the MOSFET driver inputs.

Now it seems to be stable, as we have violet noise on each gate and some serious noise on one of the MOSFETs drain, see screenshot.

But this does not generate any crackling noises anymore in the coils., even when running on 41V on the drains and with or without the 2 stackted neo's attached to the coils.

Yellow is gate 1 signal, blue is gate 2 signal and purple is MOSFET 2 drain signal.


So i think that the crackling only occurres when using this specific white noise (FM like) generated  by the Pic's.


Itsu





   

Group: Professor
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So i added again the high pass filters between the FG and the MOSFET driver inputs.
So now you re brave enough to connect your FG to this circuit ?
...or are you going to order these digital isolators from Silicon Labs or finish the EL2009 buffers ?

Now it seems to be stable, as we have violet noise on each gate and some serious noise on one of the MOSFETs drain, see screenshot.
Both drains?

But this does not generate any crackling noises anymore in the coils., even when running on 41V on the drains and with or without the 2 stackted neo's attached to the coils.
Are the two noise channels from your FG phase-synchronized ?  I know it is weird to talk about phase synch between two noise signals ...but it is possible in a digital FG.

So i think that the crackling only occurres when using this specific white noise (FM like) generated  by the Pic's.
Maybe and if so that would be highly unusual.
Let's investigate the phase of the two noise signals appearing at the two outputs of your FG, first.
   

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tExB=qr
Peter demonstrated repeatable crackling with a delay of around 220ns between his two signals.

To do anything with whatever is happening, you need predictable repeatability.
   

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Well, Itsu has a 2-ch Function Generator that can output any phase offset of any two signals down to nanoseconds with a turn of a dial.
I just do not know if he is brave enough to use it without galvanic isolators (...such as the ones from SiliconLabs).
   

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So now you re brave enough to connect your FG to this circuit ?
...or are you going to order these digital isolators from Silicon Labs or finish the EL2009 buffers ?

I made sure first without any drain voltage on the MOSFETs that there were no abnormall signals on the gates like there are when using the Pics.
But you are right, that is certainly not full proof, so i will first hook up those EL2009's before doing any further tests.
Concerning those digital isolators from Silicon Labs, do you recommend 2 single or 1 dual-channel unidirectional one(s)?

Quote
Both drains?

yes, both drains.

Quote
Are the two noise channels from your FG phase-synchronized ?  I know it is weird to talk about phase synch between two noise signals ...but it is possible in a digital FG.

Hmmm, don't think so as there seems to be no phase sync setting on the FG screen when on noise, just amplitude and offset, but i will take another look, perhaps the CH1=CH2 button?



Itsu


   

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Dear All.

Off topic, I know but...

Does anyone remember the website that sold all those " Exotic " wires ? UK based?

Kind regards, Graham.


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Nanny state ? Left at the gate !! :)
   

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Dont connect your FG, it's not worth it, i will as soon as i get a chance send you my uproc signal gen i built especially for this, you will need to add fet stages to it but i cannot see why the pcb fet drivers could not be hooked up to it.
Problem i have is that i only see day light at the weekend, but not this weekend as i am working, so i guess i can only send the weekend after this coming one  O0
Grum wires.co.uk sell all sorts of wires, not sure what you mean by exotic.?
   

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Hi Peterae.

Many thanks. That's the one.  O0

Anything other than Iron was classed as exotic in my workshop!! Old  " in house " joke !!

Cheers Graham.


---------------------------
Nanny state ? Left at the gate !! :)
   

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Thanks Peter,

with the EL2009CT buffer/amplifiers in place the FG will be protected enough.
I just need to make a neat RF tight enclosure (or 2) which will be the main problem together with a clean + and - 16V power supply.

Itsu 
   

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Concerning those digital isolators from Silicon Labs, do you recommend 2 single or 1 dual-channel unidirectional one(s)?
2 single because they offer less crosstalk and more versatile isolation. 
Just pick the fast ones. S.L. has some slow ones, too.

I just need to make a neat RF tight enclosure (or 2) which will be the main problem together with a clean + and - 16V power supply.
Just put some heavy chokes in series with the power supply lines.
The good old solderable feedthrough capacitors are a good way to get the power lines into metal enclosures ...with RF bypassing!

« Last Edit: 2016-12-08, 21:47:06 by verpies »
   

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Quote
2 single because they offer less crosstalk and more versatile isolation. 

Right, sounds logical.


Quote
Just put some heavy chokes in series with the power supply lines.

with heavy you mean mH's?


Would a simple circuit like the one below (with the heavy chokes and feedthrough capacitors added) be enough?


Thanks,   itsu
   

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with heavy you mean mH's?
Whatever you can fit in the enclosure....and beads, beads, beads on the power lines inside the enclosure BEFORE the bypass cap.

Would a simple circuit like the one below (with the heavy chokes and feedthrough capacitors added) be enough?
Yes, but the output should not have that 50Ω resistor in series (just a 0Ω direct connection) because the output impedance of this amplifier is around 1Ω and you want that because such low impedance will be very useful for driving high current loads (coils etc...) in the future.
Also, the 50Ω input resistor might be wrong because this amplifier and enclosure already have some intrinsic input impedances and that parallel input resistor should be selected to make up a total 50Ω impedance in combination with them, in order to match it to the output impedance of your FG and any coax cable. 

The way to select this input resistor it is to put a T-splitter at the FG's output and scope short-pulse reflections there, while adjusting this input resistor until these reflections are minimal ...or use a VSWR meter with a CW sine signal.


P.S.
To minimize distortions, the EL2009 might need a resistor to ground on the output pin in order to force it to always source some small idle current.  I think that is mentioned in the datasheet
   

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Thanks verpies,

i read about an optional R2 in the datasheet, which seems connected to the minus rail, but only needed when driving multiple outputs.


Itsu 
   

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The EL2008 datasheet, which is also applicable to the EL2009, states:

Quote
DRIVING "INDUCTIVE LOADS":
To prevent damage to the EL2008 when the output kicks beyond the supplies it is recommended that catch diodes be placed from each supply to the output.
So a pair of fast Schottky diodes from the output to the supply rails is a good idea, too.  Reverse-biased, of course, and rated over 2A. (40V is enough).

It is worth to keep in mind the warnings described in the "CAPACITIVE LOADS" section of this datasheet, when driving purely capacitive loads (such as driving piezos or MOSFET gates directly without a gate driver chip).
The solution to this is simple: a single resistor or an RC snubber, but you have to remember about adding them externally when driving such peculiar loads.

The "OP AMP BOOSTER" section is not applicable to your simple FG buffer, because you do not have any op-amps in it.
The only advantage of adding an op-amp to the EL2009 is that you can get more output voltage than your FG can output.

Watch this video if you ever want to play with op-amps.

« Last Edit: 2016-12-09, 16:46:09 by verpies »
   

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Hi Itsu
I forgot i had a half working day to day so managed to box up and ship the controller.

The circuit is here
http://www.overunityresearch.com/index.php?topic=31.0

and even a video on it's capabilities and how to use it
http://www.youtube.com/watch?v=tSQFbPGvcgE
   

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verpies,

I did notice the "pair of fast Schottky diodes from the output to the supply rails" when looking into the data sheets of the ELxxxx series yesterday.
I will add them to the circuit.

Thanks for the video on the op amps, it is pleasantly simple explained.


Peter,

thanks for that, it seems a very nice piece of equipment.
I will take a further look into that thread as it seems to have some additional info.

Itsu
   

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Updated EL2009  FG output protection circuit:


Itsu
   

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Looks well but I'd add 10μF SMD tantalum caps in parallel with C1 and C2.  You can get away without them if the power supply wires are very short and thick. Tight dead-bug construction is preferable for RF.
I wonder how much R1 will turn out to be.

P.S.
The ± power supply for that thing is much larger than the entire device, isn't it? ;)
I am assuming you made a dedicated ±16V linear power supply for it.
« Last Edit: 2016-12-10, 19:49:48 by verpies »
   

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Yes, these tantalum caps (no SMD) where also planned to be installed if needed.

The ± PS is indeed much larger, its a 8A ± 24V circuit board with a bulky toroid transformer.
Not sure yet if i will dedicate it to the EL2009's (adjusted to ± 16V) or that i use the ± 24V to feed into 2 separate LM337/LM317 regulators adjusted to ± 16V.
Presently that ± PS is feeding a whole range of fixed + and - regulators so i have a lot of fixed + and - voltages available for quick test purposes. 

I should have (but you never know around X-mass) all the parts the coming week.

Itsu
   

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Hi Itsu
I forgot i had a half working day to day so managed to box up and ship the controller.

The circuit is here
http://www.overunityresearch.com/index.php?topic=31.0

and even a video on it's capabilities and how to use it
http://www.youtube.com/watch?v=tSQFbPGvcgE

Peter,

i received your digital controller box yesterday, thanks.

Its a very nice piece of electronics / programming.

I put it on 24V and i understand the lower SMA center pins carry the pulse, while their upper counterpart SMA center pins carry the return signal,  right?

I increased the frequency to see more then 1 pulse on the scope and display the both signals, see screenshot.
But as the phase setting on the box was still at 0.00nS (see picture) i would expect to see the both signals in phase, but they are not.

It that to be expected or do i need to sync those signals somehow.

Itsu
   

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Hi Itsu

Thanks & glad it arrived OK.

That is right, 1 sma is gnd and the other is the signal, just my way of isolating the pulse from the case ground, i did have fet modules that screwed onto those sma's.

You are indeed correct about an offset delay, i'm trying to remember the full story but it's basically inbuilt into the delay chips, i was going to alter the software in an update to negate this but never got to v1.1  O0

OOPS i forgot to say i have the knob and back in a box in my loft but because i had very little time to wrap and send it, it went without them, but should not really be a problem.
   

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Peter,

thanks for the info, the blue signal is leading the yellow by 11nS, so i will call the blue (right hand side of the box) the primary.

No problem with the knob and back, i will use a piece of double sided PCB to close it up and a knob will be available somewhere here.


I was puzzled by the "storing" line on the display, i know it means "to store" in English, but in plain Dutch (my primary language) it means "failure".
Toke me some time to make the switch  :o


Itsu
   

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Quote
i know it means "to store" in English, but in plain Dutch (my primary language) it means "failure".
LOL

it would work fine without the bottom on as the electronics is enclosed and facing the top of the case by using a double sided pcb.
   

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You are indeed correct about an offset delay, i'm trying to remember the full story but it's basically inbuilt into the delay chips, i was going to alter the software in an update to negate this but never got to v1.1  O0
That's right.  These delay chips require a calibration to be done in software.
If you have the sources and a matching compiler, you can just hardcode the equalizing delay by adding a small integer in the IO routine.  This way you will create a firmware that will be suited only to your box with minimal effort.
   
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