User manual

Fig. 10: A ceramic capacitor (B_Kondensator.gif)

Electrolytic capacitors

You get large capacitances with electrolytic capacitors. The insulation consists of a very thin layer of aluminium oxide.

The electrolytic capacitor contains a liquid electrolyte and wrapped aluminium foil with a large surface. The voltage

may only be applied in one direction. A leakage current flows in the wrong direction and gradually degrades the

insulation layer, which leads to destruction of the component. The negative pole is designated by a white stripe and

has a shorter connection wire.

Fig. 11: An electrolytic capacitor (B_Elko.gif)

2. Step: Current gain

The circuit in Fig. 12 shows the basic functioning of the NPN transistor. There are two circuits. A small base current

flows in the control circuit; a larger collector current flows in the load circuit. Both currents together flow through the

emitter. Since the emitter is at the common reference point of the circuit, this circuit is also called the emitter circuit.

Once the base circuit is opened, no more load current flows. The base current is much smaller than the collector

current. The small base current is thus amplified to a larger collector current. The base resistor is 470 times larger

than the series resistor in the load circuit. The small base current can be identified by the low brightness of the green

LED. The transistor BC548B amplifies the base current about 300-fold so that the red LED is substantially brighter

than the green LED.

Fig. 12: An NPN transistor in the emitter circuit (Schaltung1.jpg)

Connect a second resistor of 470 k parallel to the existing base resistor. The base current thus increases, and the

collector current also becomes larger. The transistor is now fully interconnected, i.e., an even larger base current can

no longer increase the collector current. If you connect a 22 k resistor in parallel, the red LED does not become any

brighter. The transistor now works like a switch. Between collector and emitter there is only a very small voltage drop

of about 0.1 V. The collector current is already limited by the consumer and cannot increase anymore. Between base

and emitter there is a voltage of about 0.6 V which changes only slightly with a change in current.

green red