REAL DIODE

 

Schematic symbol

Diode will conduct current in the direction of the arrow of the triangle it acts like an open circuit to any attempt to establish current in the opposite direction.

The Anode terminal is in the tail of the arrow while the Cathode is in the head as indicated in the schematic symbol. I_D – is the current that flow across the diode and V_D - is the voltage drop across the diode.

 

 

 

VOLTAGE (V) – CURRENT (I) CHARACTERISTICS OF THE REAL DIODE

 

FORWARD BIAS CHARACTERISTIC

 

 

 The diode is forward bias when the current is flowing in the direction of the triangle. The diode is “ON” state thereby, the diode is conducting.

 

 

 

As shown in the graph, the maximum current will flow across the diode when the voltage in the anode reaches the threshold voltage.

The threshold voltage - is defined as the minimum voltage required before any appreciable current can flow through the diode.

Two types of diode :     a. Germanium Diode (Ge)

                                    b. Silicon Diode (Si)

 

Ge diode has a threshold voltage of 0.3V, and Si diode has a threshold voltage of 0.7V.

0.3V and 0.7V are used as a guide indicating that 0.3V or 0.7V must drop across the Ge or Si diode respectively before any significant current can flow through the diode.

 

 

REVERSE BIAS CHARACTERISTIC

 

the diode is reverse bias when the current is flowing in opposite direction of the triangle. In the reverse bias condition the diode is “OFF” state.

 

 

 

 

When the reverse bias voltage reaches to its maximum value, current will flow across the diode in the opposite direction of the triangle.

Break Down Voltage (Vb) – is defined as the approximate value of the reverse voltage before any appreciable current can flow through the diode.

 

 

 

 

 

COMPOSITE V-I CHARACTERISTICS

 

Real diode has a Threshold voltage (Vt) of 0.3V for Ge, and 0.7V for Si respectively. While the break down voltage will reach up to hundreds of volts depending on the manufacturer’s specification.