
Trícks of the trade 301
NPN
Si
α—-9V
PNP
+9 V
Figure 11.22 Separation of DC and AC functioning is illustrated by this oscillating hfe tester.
not necessarily reduce the RFI, it will merely
change its frequency distribution; after all, the
energy associated with the switching transient has
to go somewhere. A resistor in series with the
capacitor can help enormously by damping the
energy and dissipating much of it as heat locally,
reducing both conducted and radiated emission. A
resistor of 30 to 50 ohms proves about optimum in
most cases.
A technique associated with extremums is the
separation of the AC and DC characteristics of a
circuit. The ...