Mr RB
Well-Known Member
Here's the resistor divider thing I was talking about, assuming Vin is fairly constant this gives an extra voltage on Q2 base because of the R4:R3 voltage divider. Now R2 only needs to make about 0.15 to 0.2v for Q2 to turn on.
I changed the pos feedback R to a C, using two 330pF caps for simplicity, the cap values and ratio have not been tweaked but should oscillate well.
This is only 1 extra component compared to the previous circuit, but should give a lot less R2 energy loss.
It probably needs a resistor in series with Q2 base for best "RC delay" type action to slow down freq and increase efficiency, and a resistor in series with D2 zener will increase eff there too as prev discussed (to reduce current peak through zener+Q2 base clamping).
I changed the pos feedback R to a C, using two 330pF caps for simplicity, the cap values and ratio have not been tweaked but should oscillate well.
This is only 1 extra component compared to the previous circuit, but should give a lot less R2 energy loss.
It probably needs a resistor in series with Q2 base for best "RC delay" type action to slow down freq and increase efficiency, and a resistor in series with D2 zener will increase eff there too as prev discussed (to reduce current peak through zener+Q2 base clamping).