I'm facing something I cannot fully understand even though I tried for hours.
**broken link removed**
Under simulation (LTSpice and Orcad), it sometimes, under some circusntances, stops working (Q1/Q2 keep always ON, and so capacitor stops charging again, thus oscillation ends). I found it to be dependant on R1 value and Q1 hFE.
Here's an example (LTSpice).
Works - > 1.5kohm, Q1 BC847A
Does not - > 1.8kohm
**broken link removed**
**broken link removed**
If Q1's hFE is below 200 it works for some R1 values that don't work for higher Q1's hFE.
Orcad simulation has its own R1 valid range, and the output frequency differs from LTSpice's.
Q1 as BC547B leads to:
- LTSpice works for R1 as low as 800 ohm, but Orcad stops working around 1.1 kohm.
- LTSpice works for R1 as high as 1,3k ohm, but Orcad stops working around 1.9 kohm.
It seems that this kind of circuit is not very well suited for simulations. Maybe it is not a neat desing?
Thanks for any idea.
**broken link removed**
Under simulation (LTSpice and Orcad), it sometimes, under some circusntances, stops working (Q1/Q2 keep always ON, and so capacitor stops charging again, thus oscillation ends). I found it to be dependant on R1 value and Q1 hFE.
Here's an example (LTSpice).
Works - > 1.5kohm, Q1 BC847A
Does not - > 1.8kohm
**broken link removed**
**broken link removed**
If Q1's hFE is below 200 it works for some R1 values that don't work for higher Q1's hFE.
Orcad simulation has its own R1 valid range, and the output frequency differs from LTSpice's.
Q1 as BC547B leads to:
- LTSpice works for R1 as low as 800 ohm, but Orcad stops working around 1.1 kohm.
- LTSpice works for R1 as high as 1,3k ohm, but Orcad stops working around 1.9 kohm.
It seems that this kind of circuit is not very well suited for simulations. Maybe it is not a neat desing?
Thanks for any idea.