We want to see how much inductance is
contributed from protection fuses. As we know inductance of all
electrical wires increases as frequency going up due to skin
effect. Since fuses are tiny wires compared to low gauge wiring
cable, will the inductance high enough to affect amplifier's
performance? The effect of fuse inductance is increased DC rail
ripple voltage. The DC supply effectively has higher output
impedance in high frequencies.
We measure impedance of fuses represented in
R+jX (resistance and reactance). If we see positive (negative)
X, it indicates inductive (capacitive) reactance.
Measurement results of a 15 A 25 mm fuse are
shown below. The resistance is a constant value, 0.017
Ω. X is positive for all
measured frequencies. The inductance can be obtained as
L = X/2
p f
From the
measured X's, L is about 14 nH. Compared to the
resistance, the reactance is indeed insignificant.
