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Doubt about the Polish PI
Hello!
I worked with analog electronics for many years. Today I am retired and electronics is my hobby.
Recently I became interested in metal detectors.
I studied the following detectors: FB, IB, PI and pinpointer.
Among the PIs I came across the Polish PI and then my question started.
I downloaded numerous circuits from the Polish PI and in all of them I found the same stage formed by the T3 transistor.
This transistor should form a current source controlled by the output voltage of the LM741 (IC3).
This current source would modulate the frequency of the CI LM555 (IC6) configured as an astable oscillator.
The detail is that I analyzed the circuit formed by transistor T3, but I did not understand how that configuration can generate a current source.
The output voltage of the LM741 is entering through the transistor collector, which does not correspond to all three transistor operating configurations in the linear region.
There is no way for a signal to enter through the collector and exit through the emitter.
The base-collector junction is reversed-polarized, which is normal, but the base-emitter junction is also reversed-polarized, which is not normal.
I simulated the circuit in question. I used the Simetrix app.
I replaced the LM741 output with a square wave voltage source from -4V to + 4V at 100Hz, but I did not detect the load current for the LM555. So the output of the LM555 did not oscillate.
Then I changed the frequency to 1Hz and it didn't work either.
But the fact is that there are thousands of Polish IP circuits in operation around the world, so I would like someone to clarify this question for me.
Thank you!
I worked with analog electronics for many years. Today I am retired and electronics is my hobby.
Recently I became interested in metal detectors.
I studied the following detectors: FB, IB, PI and pinpointer.
Among the PIs I came across the Polish PI and then my question started.
I downloaded numerous circuits from the Polish PI and in all of them I found the same stage formed by the T3 transistor.
This transistor should form a current source controlled by the output voltage of the LM741 (IC3).
This current source would modulate the frequency of the CI LM555 (IC6) configured as an astable oscillator.
The detail is that I analyzed the circuit formed by transistor T3, but I did not understand how that configuration can generate a current source.
The output voltage of the LM741 is entering through the transistor collector, which does not correspond to all three transistor operating configurations in the linear region.
There is no way for a signal to enter through the collector and exit through the emitter.
The base-collector junction is reversed-polarized, which is normal, but the base-emitter junction is also reversed-polarized, which is not normal.
I simulated the circuit in question. I used the Simetrix app.
I replaced the LM741 output with a square wave voltage source from -4V to + 4V at 100Hz, but I did not detect the load current for the LM555. So the output of the LM555 did not oscillate.
Then I changed the frequency to 1Hz and it didn't work either.
But the fact is that there are thousands of Polish IP circuits in operation around the world, so I would like someone to clarify this question for me.
Thank you!
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