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ULN2003 Darlington pair IC – These Darlington arrays are furnished in 16-pin plastic 3 dual in-line packages (PDIP) (suffix “A”) and 16-lead surface-mountable Small Outline Integrated Circuit (SOICs) (suffix“L”).
The Series ULN2003A/L is high-voltage, high-current Darlington transistor pair arrays. IC comprises of the seven NPN Darlington pairs that feature high-current, high-voltage outputs with common-cathode clamp diodes for switching inductive loads.
The collector-current rating of a single Darlington pair is 500 mA for each of the seven drivers. The output of collector pins can be combined/paralleled for high current (in case of more than 500mA) load requirements. That’s why ULN20xxA/L IC’s are ideally suited for interfacing between low-level logic circuitry and multiple peripheral power loads.
ULN is actually comprises of transistors that’s why it has three pins base, emitter and collector. Enable (emitter) pin 8 is connected to ground for proper operation of IC (all units feature a common emitter), input are base pins from 1-7 and output are collector pins from 10-16 and pin 9 is Common cathode for freewheel diode. This free wheel diode protects from the back EMF because we know the diode does not work in the reversed direction.
ULN2003 PIN CONFIGURATION
|I – Channel 1 through 7 Darlington base INPUT
|Common emitter (enable) shared by all channels (typically tied to ground)
|Common cathode node for flyback diodes (required for inductive loads)
|O – Channel 1 through 7 Darlington collector OUTPUT
INTERNAL CIRCUITRY OF ULN2003 IC
The ULN20xxA/L have series base input resistors to each Darlington pair, allowing operation directly with 5 V TTL or CMOS.
The ULN2003A devices have a 2.7-kΩ series base resistor for each Darlington pair for operation directly with TTL or 5-V CMOS devices.
The ULx2004A devices have a 10.5-kΩ series base resistor to allow operation directly from CMOS devices that use a supply voltage of 6V to 15V.
ULN2003 IC WORKING
When we apply a positive signal to the input base of ULN2003 IC it will provide a negative output to the collector because of the inverter of the IC you can see it in the figure. A small current is able to provide signal to the ULN IC.
The purpose of the pin is to provide a flyback diode aka (also known as) catch diode aka (also known as) freewheeling diode on each output for the inductive load so that the inductive energy stored in the coil of the relay does not break down the output transistor of the ULN2003 and can possibly damage ULN IC transistors.
The common (not best) practice is to connect that pin (the internal diodes) to the relay supply voltage.
ABSOLUTE MAXIMUM RATINGS
Output Voltage, VCE
Output Voltage to (ULN200xA and ULN200xL) ……..50 V
Output Voltage to (U LN202xA and ULN202xL) ……..95 V
Max Input Voltage, VIN …………………………..30 V
Continuous Output Current
IC Collector Current (Single Output Current)…………………………………………. 500 mA (max)
ULN ICs can operate over a wide temperature range (–40°C to 105°C).