i am new here but i really like this place. I am currently studying electrical engineering at the university so i am still learning. I have a problem figuring out a circuit and i wonder if anyone could help me. The circuit is this https://www.4qdtec.com/mvbz/smv1.gif and some info about it can be found here 4QD-TEC: Multivibrators and Relaxation Oscillator Circuits . It is a series multivibrator that produces sawtooth signals. However, i can't get it to work right. I connect a dc supply between the two horizontal lines on the top and bottom of the circuit (+ goes to the top line) as well as a ground to the bottom line. I take the output from the collector of the npn transistor (the upper one). Can you help me understand how this circuit works? Also, can you help me choose the transistors and diode to make it work? Thanks a lot guys
The best results were in 9.7V and 10.2V but again the peak-to-peak is very very low. The professor asked for 1V or more peak-to-peak. Any idea? I have attached the output for the two values + the circuit
It's working. That's how it works. What do you mean, "the peak-to-peak is very small."? Your waveform is over 4V p-p. If you want to see sawtooth waveforms, look at the bases of the transistors.
Really? I was expecting the sawtooth to be visible from the collector of either transistor because that's what was written on the web site
"A nice, well behaved oscillator circuit. The diode isn't really needed but it does improve the waveform available on the emitters so that a good sawtooth is available. The values shown give a pulse of about 30µSec every 37mSec. The pulse output may be taken from either collector."
So by saying the peak-to-peak was small i meant that the "ripple" of the output was very small - it was a few mV only. I expected the linear part to have bigger incline.
In the meantime i tried moving around the "probe" and i got the best result when measuring voltage between the collector of the npn and the base if the pnp. I have attached the graph. (that's pretty much what you said about the base)
Given that's how it works, can you explain to me the step-by-step procedure of how this circuit works?
It's working. That's how it works. What do you mean, "the peak-to-peak is very small."? Your waveform is over 4V p-p. If you want to see sawtooth waveforms, look at the bases of the transistors.
Now i see what you meant. I ignored the long vertical lines because i thought it was a LTSpice (and a PSpice as well) bug. But it turns out that it was the actual output. Only instead of the lowest and highest values be connected with a straight line, that line started from way high - almost as high as the highest value.
"A nice, well behaved oscillator circuit. The diode isn't really needed but it does improve the waveform available on the emitters so that a good sawtooth is available. The values shown give a pulse of about 30µSec every 37mSec. The pulse output may be taken from either collector."
Given that's how it works, can you explain to me the step-by-step procedure of how this circuit works?
To get sawtooths (sawteeth?) from the emitters, you need to add a resistor (10k works) from the emitter of Q1 to GND, and from the emitter of Q2 to +V.
To get sawtooths (sawteeth?) from the emitters, you need to add a resistor (10k works) from the emitter of Q1 to GND, and from the emitter of Q2 to +V.
Oh i see. Well do you think the output graphs are normal? The one from the emitter of the npn is not very linear (1st attached). Also, the one from the collector of the npn seems more like an horizontal line with instant drops than a square (shouldn't the high and low times be even?) (2nd attached). The most interesting though is NPN Collector minus PNP Base (differential voltage)(last one).
Oh i see. Well do you think the output graphs are normal? The one from the emitter of the npn is not very linear (1st attached). Also, the one from the collector of the npn seems more like an horizontal line with instant drops than a square (shouldn't the high and low times be even?) (2nd attached). The most interesting though is NPN Collector minus PNP Base (differential voltage)(last one).
I tried what Ron said (tampered the capacitors a bit to make the sawtooth last longer) and it works well. I might add it as an "Appendix". I have attached the output from the PNP emitter.
Could you explain to me how this circuit actually works? (capacitors charging, then transistor goes on, etc)? Thanks
Do you think i suggest taking the output between the NPN collector and the PNP base (it was the best graph) or would it be 'theoretically' wrong?