Roff
Well-Known Member
Look at them carefully, and redraw one of them if you need to.wmmullaney said:OK, well mine seemes to operate on a differant principle.
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Look at them carefully, and redraw one of them if you need to.wmmullaney said:OK, well mine seemes to operate on a differant principle.
whiz115 said:it's the same wmmullaney...but unfortunately it doesn't work, you must
find transistor with the specific properties to make it work.
wmmullaney said:Did you use 12v? I kinda want to use 5.
Nigel Goodwin said:Google for "astable multivibrator" - two transistors, works off 5V, easy to do what you want.
fingaz said:It does work. Try using a 47khm: resistor, 100:mu: F capacitor and a BC547B with a RED led.
Torben said:[Edit: I don't know if this can be simmed in LTSpice. If so, I don't know how.]
whiz115 said:yes it does work with your 47K modification... and with 100K but only with
2n2222 in metal can! i also tryed 2n3904 and it didn't worked... it lights stable i haven't tryed bc547..
1k resistor fills the capacitor too fast? why the schematic says 1K???
i don't see how LTspice can simulate such thing... it's an undocumented function...
It has nothing to do with LTspice and everything to do with the transistor spice models. I have never seen a model that includes Vbe breakdown, much less the negative resistance of the Vceo breakdown.whiz115 said:yes it does work with your 47K modification... and with 100K but only with
2n2222 in metal can! i also tryed 2n3904 and it didn't worked... it lights stable i haven't tryed bc547..
1k resistor fills the capacitor too fast? why the schematic says 1K???
i don't see how LTspice can simulate such thing... it's an undocumented function...
Roff said:It has nothing to do with LTspice and everything to do with the transistor spice models. I have never seen a model that includes Vbe breakdown, much less the negative resistance of the Vceo breakdown.
It is a function of where the load line intersects the VI curve of the Vceo breakdown. The red line below is representative of the general shape of the Vceo breakdown VI curve. The blue lines are examples of load lines that will and will not oscillate. As you can see, in order for oscillation to occur, the load line has to intersect the breakdown curve in its negative resistance portion. The one that doesn't oscillate intersects the positive resistance portion of the curve, and is therefore a stable bias point.whiz115 said:Roff do you know why the design uses so much small resistor? 1K it was impossible to make it work but it worked fine with a 47K at 12V