very high and powerful voltazh voltage from a small voltage

[gyulasun]

Hi Mags,

To be more precise from my part, and to correct a bit my rusty memories, the coil's L inductance in directly series with the collector electrode which is basically 'responsible' for the frequency, together with its transformed L towards the base electrode where the R bias resistor is, they constitute the L/R time constant.   And the core saturating characteristics is also involved, please study this page http://www.tpub.com/neets/book9/36e.htm  at mainly the bottom part, though the one transistor oscillator circuit is not exactly the same like the one shown here,  still the operation must be very similar. And there you can read the last sentence: "From T1 to T2 (figure 3-34), transistor Q1 is held at cutoff by C1 discharging through R1 (figure 3-33). The transistor is now said to be "blocked." As C1 gradually loses its charge, the voltage on the base of Q1 returns to a forward-bias condition. At T2, the voltage on the base has become sufficiently positive to forward bias Q1, and the cycle is repeated."

So while the ON time of the oscillator mainly depends on L/R and the core, the OFF time is controlled by C1 which is not present in a component form in the present 'welding' oscillator circuit like in my link, however  this is where the base-emitter capacitance comes into the picture.  I recall when I tinkered with such blocking oscillators, I placed a 22pF capacitor in parallel with the base-emitter  and this changed the frequency from the 20-30kHz range down to the 10-20kHz range (a huge change in this low frequency oscillator circuits)  because I dramatically changed (increased) the few pF base-emitter capacitance. 

Now your questions may be answered,  the secondary coils do not normally change too much the frequency (unless the load forces the core into saturation, this would influence L/R, but then this is not a normal operation),  and when you were to control the base from an outside source, the circuit switching properties would be dictated mainly by the rise and fall times of the input pulse and its duty cycle.  Probably the latter choice sounds better bringing in more flexibility but this should be tested of course.

rgds, Gyula

[Jimboot]

Hi Jim, 

Very good and please try to estimate output-input power relation when you have some time.

Gyula

Will do some scope shots tonight and put an ampmeter on. The dmm was unable to measure output. Same issues as when on slayer exciters. High freq?

[d3x0r]

The oscillation happens because of the sensing coil to the base; the frequency is most dependant on number of windings form power to collector and power to base; a shorter wire to base gives shorter pulses, a shorter wire to collector gives faster pulses (when dealing with few windings).  the transistor will affect the switch time of the pulse; which determines how much of a spike you can generate to pick up on the pickup coils.  there's a thread 'joule thief 101' which does good covering this sort of circuit.  you can have just a few windings, the minimal windings is one through the toroid to the base and one through the toroid to the collector, this is also the highest frequency.  The size of resistor between the base and it's coil also determines the slope of the spike.  More than 0Ohm is good, the 101 thread says it should be 4.7K; I find with my smaller transistors that 50-100ohms works best, otherwise the slopes become more gradual and you can't get the same peek out... but I think for higher current transistors that probably a higher resistance will be better...


metglas site had some DC reactor ideas; their toroids, when, saturated start working like a diode, I think part of this is what happens in the joule thief idea; once the toroid saturates with a field, it stops conducting.  I dunno there's a different explaination in the first few messages of that joule thief 101 thread...

[gyulasun]

Will do some scope shots tonight and put an ampmeter on. The dmm was unable to measure output. Same issues as when on slayer exciters. High freq?

Well, it is not high frequency  but for a DMM designed and calibrated for 50/60 Hz AC it is high.  Woopy had 2.7kHz frequency and Sergdo had around 10kHz oscillator frequency.

[enron-r-crooks]

This circuit reminds me of
https://lh5.googleusercontent.com/-aPCjW6I-9-c/TnMk95PlPpI/AAAAAAAAAS8/F5_qKZpbYho/s720/000f2eqf.jpg
Barret - Tesla's nonlinear oscillator-shuttle circuit
http://www.scribd.com/doc/248237/Barret-Teslas-nonlinear-oscillatorshuttle-circuit-OSC-theory