Exciting a resonant tank with pulsed DC - help

[madddann]

Hi Gyula, thanks for the suggestions, will try that today or tomorrow and report back.

Hi Forest, my circuit is just the arduino on a protoboard with the opto (both powered from 4x1.5V + small dc-dc converter to get 5V). The trasistor is also on the protoboard. The tank circuit, the current sensing resistor (0.1ohm) and the 4.7 ohm resistor are connected with clipleads to the starter battery and transistor.
this is all experimental setup right now, just to see how things behave.

Maybe you got confused by the Figuera schematics in my gallery - those were old experiments from the Figuera thread that didn't show much results, but I still learned some things from them.
I removed those pics now, so no more confusion.

Thx for your interest.

Dann

[madddann]

Hi Gyula and everyone else.

Sorry for the very long delay, but life just happens the way it does.

I tested the suggested circuit, but was unable to make the transistor to switch solidly, at best it was switching just faintly when tested with an automotive 10w bulb (the bulb had an lazy effect to turn on and off). Switching  the tank circuit did not yeld any results at all.

The waveform on transistor base-emitter was a square wave, but the ON state was just about 30mV difference from the OFF state. I tried some resistors from 1.8k to 470 Ohm, I did not try a lower value because I think the opto can't handle the current.
Another resistor on the base-emitter did not help at all.
This transistor that I'm using (E13007-2) needs from 0.4A to 2A base current (from PDF), I think the opto is unable to drive it directly.

I also did a simple reverse polarity (reverse current) test on the transistor's collector-emitter with a 12v battery and 10w automotive bulb.
I connected + to emitter and - through the bulb to the collector, and guess what, the bulb lit almost fully up (the base was not connected to anything).
I think that this is exactly what happens here in this scopeshot - where the oscillating wave is cut off: https://postimg.cc/image/gmexmps2t/

Now I have the following question - what kind of semiconductor component would be able to do the switching in this circuit without cutting off the oscillation (when current reverses)?
Do IGBTs without a body diode exsist?

Anyone with an idea or possible solution is welcome to post it here.
Now I have some time (till Sunday) to test things out with what I have at hand.

Thanks Gyula and all!


Dann

[gyulasun]

Hi Dann,

The transistor is very likely defective, it should not conduct in the reverse voltage test. Also, the 30mV difference between the on and off states indicates that.
The reason I suggested to connect the opto output across the base and emitter was that in that case the base current would come directly via the the 1 kOhm resistor from the +12V rail and not through the opto with its 50 mA max output current. The opto would shunt the 0.7-0.8 V forward voltage of the base-emitter to as low as 0.1-0.2 V or so (to its own saturation voltage) and yes, less than 470 Ohm should not be used without abusing the opto, in this respect the opto is a limiting factor if a good power transistor you use for switching needs a minimum of some hundred mA base current.

Yes, there are IGBT types without the body diode, here is one of the manufacturers types from random search:
https://tinyurl.com/yd9uj85f
(notice switching speed data for them)

and see and check digikey for instance

https://tinyurl.com/y7a5roga   (notice I did not check here all whether they have body diode or not)   

for instance Microsemi's APT25GR120:
https://tinyurl.com/y9grabqw

To drive an IGBT, you could follow the same latest opto circuit you used, where its output is connected across the gate-emitter of the IDBT and the gate would get the +12V from the 12V rail via also a few kOhm resistor.

Or you may wish to use a dedicated MOSFET gate driver to drive the IGBT, it may not be an overkill for your relatively low frequency tests.


Gyula

[madddann]

Hi Gyula!

Well, I just tested 7 transistors in the reverse voltage test: 2X E13007-2, 3X E13007-1 and 2X D13009
They all behave the same - the bulb lights up at about half brightness (in my previous post I wrongly stated that the bulb lit up at almost full brightness - it was at about half brightness).
I very much doubt that all of the transistors are defective, what I think is that they work in the negative resistance region as explained in this video: https://www.youtube.com/watch?v=rpGOKGrcpAk

Thank you for all the links and suggestions, I think I'll order two or four IGBTs and see how that goes.
So that leaves me with nothing to experiment with this circuit for this weekend, well, I'll have fun with some other things to test then.

Others are still welcome to post any thoughts and Ideas.

THX!

Dann

[forest]

You must know that circuit in simulation is not the same as circuit on workbench. I learned that hard way when I was unable to switch off my circuit without receiving a bolt of electrostatic discharge.
Circuits are not isolated in space and sometimes you find the strange factors which enable external energy filling space around ;-) You posted no picture of your circuit , that's fine. Now your turn to find the anomaly