Testing the TK Tar Baby

[TinselKoala]

I mean.... if you asked Ainslie to explain in simple words the differences between these two scope shots... what would she say? Of course she would never deign to "teach" us by explaining these shots... But it is curious that the positive gate signal in one shot results in a lot of current in the CVR.... and the positive gate signal of the same magnitude or perhaps even a bit more,  in the other shot... does not.

[TinselKoala]

TK,

That is what I meant when I said I did not believe she understood an FG is bipolar and that she was speaking in terms of absolute and not relative voltage.  She apparently believes that somehow the FG is applying a positive voltage directly to the gate of Q2 causing it to turn on.

All the discussions regarding current flow thru the FG were for nought as the concept of the Q2 source needing to be less negative than batt- was not even understood.  Good luck making the circuit oscillate without pulling Q2's source negative wrt the batt-.

Why on earth did you go to all that trouble to bulid the inverting charge pump? 

PW

The inverter was so that the oscillations could be produced without using any external bias supply. Using the inverter powered by the lowest battery in the stack, I get that -12 volts wrt the main battery "zero" that is needed for the oscillations. The basic circuit I built can't really supply the current needed to get to 200 mA without heating up the 555 to instability, as you "hinted" some time ago, of course, but it works as a proof of concept, makes the oscillations without a separate supply of any kind, and can even be used to power the "upside down" 555 timer to make pulsating negative bias drive with oscillations. None of the methods I've used so far can make the bipolar pulse needed to produce the oscs on the "off" part and the high current on the "on" part as shown in Fig5 though... that will need a better charge pump and an op-amp offset stage, I think. There is no difficulty whatsoever if a floating external bias supply can be used-- it's only when the bias must be run off the main battery that the issue of "more negative than the negative rail" becomes a difficulty.

[picowatt]

TK,

I have enjoyed the technical discussions on this thread with you, MH, .99, GL, Mags and all others who have some technical background or desire to learn.  The "circular arguments", not so much.

I have some client work to get busy with for the next ten days or so.

I'll check in when time allows to see how it is all going.

PW

[picowatt]

The inverter was so that the oscillations could be produced without using any external bias supply. Using the inverter powered by the lowest battery in the stack, I get that -12 volts wrt the main battery "zero" that is needed for the oscillations. The basic circuit I built can't really supply the current needed to get to 200 mA without heating up the 555 to instability, as you "hinted" some time ago, of course, but it works as a proof of concept, makes the oscillations without a separate supply of any kind, and can even be used to power the "upside down" 555 timer to make pulsating negative bias drive with oscillations. None of the methods I've used so far can make the bipolar pulse needed to produce the oscs on the "off" part and the high current on the "on" part as shown in Fig5 though... that will need a better charge pump and an op-amp offset stage, I think. There is no difficulty whatsoever if a floating external bias supply can be used-- it's only when the bias must be run off the main battery that the issue of "more negative than the negative rail" comes up.

TK,

Surely you know I intended sarcasm with the "why did you build the inverting charge pump" remark.

Possibly you should just consider an additional battery in the battery string, using the additional battery as a negative voltage source.  You could tap the first battery above ground for +12 volts and you would then have plus and minus 12 volts to work with.  You could run a 555 off the ground and -12 supply and run the output to an NPN (or another MOSFET) with the emitter (or source) tied to -12volts.  A pullup resistor of 10K or so can be connected between the collector (drain) and the +12 volt supply tap.  Use either 50R from the collector (drain) to the Q2 source and Q1 gate.  You can vary the 50R for your Q2 bias point and Q1 will always be fully on.  All bias current will flow thru the NPN (or MOSFET) so heat will be less of an issue wrt the 555.  Turn on/off will be a it slow with the 10K or so pullup but at the long cycle times, probably not an issue.  A lower value pullup will speed things up but at the expense of increased quiescent current. 

You could use a similar supply scheme as above and make an astable out of an opamp.  Pick an opamp that can handle the plus/minus 12 volt supply (555 can't).  You can use low power duals or quads and use the last opamp stage with a NPN/PNP output buffer to handle the current and keep rise/fall times fast.   

You can do the same things with your inverting charge pump for the minus supply, and if your 555 circuit almost makes enough current, you can always parallel a pair.  I would stay with individual 555's as opposed to a 556 dual though as heat will be an issue.

Just a few thoughts,

PW

 

[Rosemary Ainslie]

All that 'spin'.  LOL.

I've just read through the last 10 posts or so in answer to my one.  It seems I must put out 10 times the effort - when - in FACT - I only need the occasional post.  Thank you God.

picowatt - Leon - FTC - ALL - you're wasting your time.  I'll disprove EVERYTHING that you claim is conclusive.  And - to boot - it's EASY to disprove.  That last video by TK's is a PRICELESS effort at misdirection.  He claims that there is a current flow from the function generator.  He therefore replaces the battery supply with a rechargeable CAPACITOR - and lo and behold.  The oscillations DIE.  And what does he claim?  That the the function generator IS supplying energy.  IF the function generator WAS supplying energy - then the CAP would NOT DISCHARGE.  Self-evidently.  It's all spin and heavy applications of too much tar.  And it relies on the utter stupidity of all the readers here. 

He's the only guy that I know who can claim a DISPROOF - through the circuitous route of demonstrating its PROOF.  And the joke is this.  They all aver that I've 'missed the point'.  Just watch the next 10 posts or thereby.  LOL.   Long may that last.  Fortunately our readers are NOT the idiots that they - that gang of vigilantes - hopes.


Rosie Pose.