04-07-2020, 04:00 PM
All rectifiers / diode detectors have a DC circular path.
A peak detector:
input cap is charged by D1, then Input cap is discharged by D2 into load. Input cap has only AC, circular DC path is D1, D2, Load resistor, earth, D1 etc.
As shown it's working due to reverse DC leakage in the diode and -ve Space charge accumulating on the grid. As drawn, the grid capacitance would gradually charge to near HT via D1 if there was no negative space charge. That's why it either needs a transformer, an input resistor to 0V, or a 2nd diode at the input of the diode and a high value load resistor on the diode and 100pF cap, so maybe 1M or 2.2M and the cap could be 220pF or even 470pf to reduce RF on the output valve.
So it works due to parasitic capacitances and resistances and grid space charge. The bias and low pass RF filter time constant are not well defined. All diode detectors/rectifiers are either charge pumps (more than one diode) or else have a DC path on both sides, otherwise performance is undefined.
A peak detector:
input cap is charged by D1, then Input cap is discharged by D2 into load. Input cap has only AC, circular DC path is D1, D2, Load resistor, earth, D1 etc.
As shown it's working due to reverse DC leakage in the diode and -ve Space charge accumulating on the grid. As drawn, the grid capacitance would gradually charge to near HT via D1 if there was no negative space charge. That's why it either needs a transformer, an input resistor to 0V, or a 2nd diode at the input of the diode and a high value load resistor on the diode and 100pF cap, so maybe 1M or 2.2M and the cap could be 220pF or even 470pf to reduce RF on the output valve.
So it works due to parasitic capacitances and resistances and grid space charge. The bias and low pass RF filter time constant are not well defined. All diode detectors/rectifiers are either charge pumps (more than one diode) or else have a DC path on both sides, otherwise performance is undefined.
