ULN2803 and ULN2003 are Darlington array ICs used to interface Logic circuits, such as microcontroller circuits, to high power devices. During the early days of your electronics tour, you may not understand the difference between these two ICs. This blog is to give you an idea about the major difference between these two ICs.

ULN2003A
ULN2003 is a seven-channel Darlington array used to interface microcontrollers to high voltage, high current devices such as solenoids, lamps, relays, etc. It has the capacity to drive  500mA into a single channel, up to 250mA per channel if four of the seven channels are active and 125 mA per channel if all the seven channels are active. Its output has clamp diodes for transient suppression to protect the low-power microcontroller circuits.
The ULN2003 is the replacement for the ULN2803 when using the Prop-1 Trainer Board or when using P7 (Prop-1) or P15 (Prop-2 and Prop-SX) for serial communications with devices like the AP-8, DC-16, FC-4, and RC-4.

ULN2803 is an eight-channel Darlington array used to interface microcontrollers to high voltage, high current devices such as solenoids, lamps, relays, etc. It has the capacity to drive  500mA into a single channel, up to 250mA per channel if four of the eight channels are active and 125 mA per channel if all the eight channels are active. Its output has clamp diodes for transient suppression to protect the low-power microcontroller circuits. ULN2803 is commonly used for controlling large seven-segment displays.