Radio and Electronics (DED Philippinen, 66 p.)
 9. ACTIVE COMPONENTS -1- DIODES
 9.2. THE PN-JUNCTION OR DIODE
 (introduction...) 9.2.1. PN-JUNCTION CONNECTED TO VOLTAGE 9.2.2. CHARACTERISTICS OF A PN-JUNCTION OR DIODE 9.2.3. ZENERDIODE

### 9.2.2. CHARACTERISTICS OF A PN-JUNCTION OR DIODE

The behaviour of such a junction as explained up to here would look like fig. 89 a. If we look at it from a general point of view we find on the left side (at reverse direction) no current at any voltage (infinite resistance) and on the right side (forward voltage) no voltage necessary for any current (no resistance).

fig. 89a

We see: this component behaves like a valve which lets flow current only in one direction. The symbol is shown in fig. 89b. It is called a DIODE and its terminals are called ANODE and CATHODE (these terminals are originated from the valve diode).

fig. 89b

But the characteristics shown in fig. 89a is only a theoretical one. We can use this imagination for simple considerations in circuits with diodes.

In reality the characteristics is shown in fig. 89. The difference is:

- in reverse direction exists a voltage-limit.

If we increase the reverse voltage above this limit there will flow suddenly a strong current which will destroy the diode at once. This limitting voltage is called BREAK THROUGH VOLTAGE.

- In Forward direction at first a voltage is needed to get any current flowing, this voltage was mentioned already above, and it is called the: THRESHOLD VOLTAGE.

- Additional the diode still needs some voltage to let flow some forward cur rent which means it has a certain resistance which is called INTERNAL RESISTANCE

fig. 89c