
Electrical and electronic principles
22
Figure 1.29 Darlington pair
Denition
Reactance: The non-resistive
component of impedance in an
AC circuit, due to the effect of
inductance or capacitance or
both. It also causes the current
to be out of phase with the
voltage.
Key fact
The Darlington pair
conguration is used for many
switching applications.
The principle of the lter circuits is based on the reactance of the capacitors
changing with frequency. In fact, capacitive reactance, X
c
decreases with an
increase in frequency. The roll-off frequency of a lter can be calculated as
shown:
where: f = frequency at which the circuit response ...