ULN2803 IC

Pandi December 16, 2014 2 min read

Bring in some muscle to your output pins with 8 mighty Darlington’s! This DIP chip contains 8 drivers that can sink 500mA from a 50V supply and has kickback diodes included inside for driving coils.

The ULN2803 is a high-voltage, high-current Darlington transistor array. The device consists of eight NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The collector-current rating of each Darlington pair is 500 mA. The Darlington pairs may be connected in parallel for higher current capability.

Applications include stepper motor, relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers, and logic buffers. The ULN2803 has a 2.7-k series base resistor for each Darlington pair for operation directly with TTL or 5-V CMOS devices.

Features:

Internally frequency compensated.
Large DC voltage gain: 100 dB.
Very low supply current per operator essentially independent of supply voltage.
Low input bias current: 20 nA (temperature compensated).
Low input offset voltage: 2 mV.
Differential input voltage range equal to the power supply voltage.
Large output voltage swing 0 V to (VCC – 1.5 V).

Application of ULN2803:

Now we see example where it is employed in practical application, suppose if you want to interface the stepper motor with the any of the Arduino boards what happens if you connect the stepper motor directly with the Arduino, Stepper and DC Motors can send spikes of current back to the controlling circuitry when switching from on to off due to inductance, as well as possibly drawing more current than your Arduino is designed to supply which will damage your board. In that case we need ULN2803 IC which works on the principle of TTL logic it has sort of 8 input with 8 outputs with 500mA thereby we drive our stepper motor efficiently without damaging our board.