It Is Used To.....
Ø ULN2803 is a High voltage, high current Transistor Array IC’s
Ø It is used especially with Microcontrollers where we need to drive high power loads.
Ø Thic IC consists of a eight NPN Darlington connected transistors with common Clamp diodes for switching the loads connected to the output.
Ø This IC is widely used to drive high loads such Lamps, relays, motors etc.
Ø It is usually rated at 50v/500mA.
PURPOSE OF ULN2803:
Ø Most of the Chips operates with low level signals such as TTL, CMOS, PMOS, NMOS which operates at the range of (0-5)v and are incapable to drive high power inductive loads.
Ø However this chip takes low level input signals (TTL) and use that to switch/turn off the higher voltage loads that is connected to the output side.
WORKING OF ULN2803:
Ø The ULN2803 IC consists of eight NPN Darlington pair which provides the proper current amplification required by the loads.
Ø We all know that the transistors are used to amplify the current but here Darlington transistor pairs are used inside the IC to make the required amplification.
Ø A Darlignton pair is two transistors that act as a single transistor providing high current gain.
Ø In this pair the current amplified by the first transistor is further amplified by the next transistor providing high current to the output terminal.
Ø A Darlignton pair is two transistors that act as a single transistor providing high current gain.
Ø In this pair the current amplified by the first transistor is further amplified by the next transistor providing high current to the output terminal.
Ø When no base voltage is applied that when is no signal is given to the input pins of the IC , there will be no base current and transistor remains in off state.
Ø When high logic is fed to the input both the transistors begin to conduct providing a path to ground for the external load that the output is connected.
Ø Thus when an input is applied corresponding output pin drops down to zero there by enabling the load connected to complete its path.
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