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ScotchTapeLord

Fri Oct 01 2010, 03:38PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

Artikbot wrote ...

@ScotchTapeLord: Just like happens with P-channel MOSFET? So essentially the stupid Yenka is exaggerating with the current flow. And this time I got it, I need to use an N-channel because electrons transfer energy WAY faster than holes :)

What I just said had nothing to do with the makeup of the transistor. The speed of a P channel MOSFET is plenty fast enough to work in a circuit like this, but your circuit is configured for an N channel device.

The gate of a MOSFET is a capacitor. To turn it on, you must charge it. In an N channel MOSFET, the gate must be charged with respect to the source... The current can be traced right out of the 555 (pulled HI) timer to the ground. In a P channel MOSFET, the gate must be grounded with respect to the drain, in which case the current is traced from V+ to the 555 (pulled LO)... but wait, there's an inductor in the way! The inductor, with its reactive impedance, resists the current flow and your switch doesn't turn on or off as quickly as you want! Ohnoes... so switch back to N channel.

That is why you can't use a P channel FET with this particular configuration.

When you apply a sharp rise in voltage across an inductor, it acts as an open circuit at first! No current! It requires time to build up. You will understand this when you're done reading up on reactance.

Artikbot

Fri Oct 01 2010, 06:04PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

@GhostNull

I wasn't being sarcastic! I'm really enjoying all this work, trust me :)

Impedance, that makes me think about loudspeakers :P Okay I promise to read all that documents. Got plenty of time this weekend :)
Thanks for the effort of searching all that information for me, I really appreciate it :D

About the components, after some time pressing my local retailer seller, she found out an old, very old (or at least it's VERY dusty) catalog with all part nÂºs she can order, and voilÃ ! She can supply me the MOSFET, the SCR, the NE555 timer, the op-amp, the resistors, the pots, the capacitors, the diodes, the drilled board... essentially everything but the inductor which I'm gonna get from CoilCraft Scotland. 12â‚¬ for everything but the inductor, seems a good deal to me (I got two NE555 just in case I burn out one... can happen :P).
Everything is arriving on wednesday! Hopefully Coilcraft's inductor will be here by friday, so I can start to build the whole thing by saturday's morning.

Thanks for the divider link! Really useful, gonna try and see what happens.

@ScotchTapeLord: Oh. Once again I misunderstood what I red. So, P channel was so slow on my circuit essentially because the impedance of the inductor was limiting its current flow, therefore slowing it down? Seems I got it this time :P Thanks!

Gonna read what GhostNull posted and see if I get that concept of current having to build up :)

Thanks to both of you once more!

Edit: Something is not working properly. Since I plugged in the comparator, my current doesn't stop from making current going as if it was AC instead of DC, going back to the inductor despite the diode is there.

A pic to illustrate. Check the current directions... Totally inverted. I'm a bit shocked, gotta admit it. Resistor values for comparator are now the adequate ones for 3V input from both fully charged cap bank and from 9V supply.

The comparator is a 741, seemingly it works flawlessly for this purpose, and it's what my local retailer can offer to me. I based on this schems:

but with inverted input/output. Seemingly it should be inverted for the purpose I'm serving. Tried the other way around and BAM half circuit blows up, and 740V flow thru the 555. So I guess it goes in the way i've put it :P

ScotchTapeLord

Fri Oct 01 2010, 06:44PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

Artikbot wrote ...

@ScotchTapeLord: Oh. Once again I misunderstood what I red. So, P channel was so slow on my circuit essentially because the impedance of the inductor was limiting its current flow, therefore slowing it down? Seems I got it this time :P Thanks!

It was limiting current flow from DRAIN to GATE, which is required to turn a P FET on, whereas N FETs are turned on by charging the gate with current from GATE to SOURCE.

Oh, and the impedance of a loudspeaker is no different electrically from the impedance of an inductor. One's just louder. Yes, you will hear your inductor.

Artikbot

Fri Oct 01 2010, 07:08PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

Aaaaah there it is the real difference!!

Darn Wikipedia, I wasn't able to understand what was written here. So essentially what changes is the way current flows from gate to the other terminal, right? And in this case, I was in the need of the N channel because it had no restrictions while feeding it, in opposition to the restriction in flow that impedance put on the P-channel.

Woah. This is deeper than I thought! :P

PS: I updated my post with a new problem.. Could you mind reading it? Thankies!

ScotchTapeLord

Fri Oct 01 2010, 08:26PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

Solution:

Artikbot

Fri Oct 01 2010, 09:03PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

ROFL. I got it downloaded :P

So, you suggest firing Yenka to avoid more problems, right?

That's what I'll do, thanks!

Will upload the file as soon as possible :)

GhostNull

Sat Oct 02 2010, 07:39AM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

LT spice is another one:

Artikbot

Sat Oct 02 2010, 11:35AM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

Omg, I found LTSpice way easier to use than PSpice, so here it goes my new schem. I've simulated it (don't know really well how does it work tho)

So far, MOSFET values won't kill it, Cap reaches 126V in no time, and says nothing about the OpAmp.

I guess when the parts arrive I'll start to experiment with them... I got two OpAmps in case I blow one, hopefully nothing will blow up.

Artikbot

Sat Oct 02 2010, 04:49PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

HOLY TRUMPETS SOUNDING ON THIS GLORY DAY

I made the circuit work 100% under Yenka!!!!

HAAAAAAALLELLUJAH, HAAAAAAAAAALLELLUJAH, HALLELUJAH, (...)

My mistakes: I didn't feed the opamp properly (LOL) and the reference voltage was being gathered from the oscillating output (LOL again). I decided not to mess up with resistors, and fed the reference right out of the box with the 7.4V my battery is capable delivering, and applied a divider to the inverting input to leave the voltage with the caps at ~325V at 7.4V. AND IT WORKS!

Okay, no more delays, here it goes the final working schem :)

Oh, and btw, the voltage inversion issue has been solved too ^^

Forget about the resistor before the inductor, the REAL coilcraft inductor has got a series resistance of 0.47Ohm. Just like the one I used on my simulations :)

I'm uploading a video to YouTube to show it working, just in case something goes bonkers and I don't realise.

And once again, VERY VERY VERY VERY thank you to everyone who helped me to develop this nerve-destroying and bite-nailing machine

We can officially rename this thread to a "how to wire all that stuff on a proto" heheheh

Edit: Here's the video link:

Adam Munich

Sat Oct 02 2010, 05:12PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Awesome. I may actually build that when I have some cash to blow. I expect this thread to be continued with you're building of the circuit IRL too.

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