Darlington Transistor Symbol
A Darlington transistor symbol, also known as schematic symbol, usually shows two transistors inside a single encapsulation. It is possible to get these transistors in NPN and PNP versions and is made of the same type of transistors. Although the basic symbol is simple, many newer transistors show more components in the schematic symbol. For example, the TIP122 package has two resistors and a diode. It is also possible to get an array IC such as the ULN2003a, which contains seven NPN Darlington pairs in the package. However, its schematic symbol contains three resistors and three diodes for each equivalent circuit.
NPN Darlington Symbol
NPN Version
PNP Darlington Symbol
PNP Version
Darlington Packages
Darlington | Ic (A) | Type |
TIP122 | 5 | NPN Transistor |
BC517 | 1.2 | NPN Transistor |
BD679 | 4 | NPN Transistor |
BC618 | 1 | NPN Transistor |
ULN2803 | 0.5 | Array IC |
ULN2003A | 0.5 | Array IC |
For switching applications such as a relay driver, or motor driver, the NPN type is used. The majority of calculators for working out the values of the biasing resistors tend to be for the NPN type as well.
Applications
Darlington transistors have many applications. Here are examples of just some modern day applications.
- High power switching
- Power amplifier
- Power supply switching
- Relay driver
- LED driver
- Motor control
- H bridge circuits