[ §2 · calculators · feedback strength ]

SSTC feedback strength

No other calculator does this. It gives the primary current at which the feedback loop takes control away from the self-oscillator, which tells you whether the oscillator has long enough to drag the coil onto the upper pole.

CT ratio N:1burden, total · Ωlead inductor · µHfrequency · kHzclamp diode drop (0.7 silicon, 0.3 Schottky) · Vprimary current, peak · A

impedance |Z| 6.33 Ωfeedback strength 39.544 mV/A (0.0395 V/A)clamps open at ~17.7 A (11.1 % of peak) known window 20.000 to 35.700 mV/A low edge: davekni, simulation high edge: Rafft, working hardware ← weighs more Just above the window (×1.11 of Rafft).The oscillator has little head start.

formula

|Z| = √(R² + (2πfL)²)        strength = |Z| / N   [V per amp of primary]
clamps open at I = V_f · N / |Z|

limits

The metric is sound. |Z|/N, and comparing two builds by it, is plain arithmetic.

The absolute takeover current is less certain. The page computes when the clamps open, and that is not proven to be the moment feedback wins. Pinning that down needs the amplitude of the oscillator’s ramp at the comparator input, which has not been measured.

The reference window is wide. davekni’s simulation (zero bridge delay, almost no lead) gives 0.020 V/A; Rafft’s working hardware at 49° of lead gives 0.036. The factor of 1.8 between them is the real uncertainty. Rafft also runs a different comparator (MAX913) and R5 = 6 kΩ. Give Rafft more weight, since his figure comes from hardware.