Introduction to the ULN2003 IC

The ULN2003 is a monolithic high voltage and high current Darlington transistor array. It consists of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The collectors are connected to the common outputs, while the emitters are grounded. The integrated clamp diodes suppress switching transients from inductive loads.

Key Features of the ULN2003

• Contains seven NPN Darlington pairs with common emitters
• Output current rating of 500mA per channel
• Output voltage up to 50V
• Integrated suppression diodes for inductive load driving
• Inputs compatible with various types of logic
• Inputs pinned opposite outputs to simplify board layout
• Enable inputs provided to disable some or all channels
• Thermal shutdown protection
• Output clamp diodes included for transient suppression
• Outputs can be paralleled for higher current capability

ULN2003 Pinout and Pin Description

The ULN2003 IC is available in 16-pin PDIP, SOIC, and TSSOP packages. The pinout and pin descriptions are as follows:

Pin Number	Pin Name	Description
1	I1	Channel 1 input
2	I2	Channel 2 input
3	I3	Channel 3 input
4	I4	Channel 4 input
5	I5	Channel 5 input
6	I6	Channel 6 input
7	I7	Channel 7 input
8	GND	Ground
9	COM	Common emitter connection
10	O7	Channel 7 output
11	O6	Channel 6 output
12	O5	Channel 5 output
13	O4	Channel 4 output
14	O3	Channel 3 output
15	O2	Channel 2 output
16	O1	Channel 1 output

Input Pins (I1-I7)

The ULN2003 has seven input pins, I1 through I7, one for each of the seven Darlington pairs. These inputs are compatible with various types of logic, such as TTL and CMOS. When an input is high, the corresponding output is active (low). When an input is low, the corresponding output is inactive (high).

Output Pins (O1-O7)

The ULN2003 has seven output pins, O1 through O7, one for each of the seven Darlington pairs. Each output can sink up to 500mA of current. The outputs are open-collector, meaning they require an external pull-up resistor to function properly. When an output is active (low), it can sink current from the load connected to it. When an output is inactive (high), it is effectively disconnected from the load.

Common Emitter Pin (COM)

The common emitter pin, COM, is connected to the emitters of all seven Darlington pairs. This pin should be connected to ground for proper operation of the ULN2003.

Ground Pin (GND)

The ground pin, GND, is the common ground connection for the ULN2003. It should be connected to the system ground.

ULN2003 Internal Architecture

The ULN2003 consists of seven NPN Darlington pairs with common emitters and integrated flyback diodes. Each Darlington pair is composed of two bipolar junction transistors (BJTs) connected in a Darlington configuration, which provides high current gain and allows the IC to drive high current loads.

Darlington Pair

A Darlington pair consists of two BJTs connected in such a way that the current amplified by the first transistor is further amplified by the second transistor. This configuration provides a much higher current gain than a single transistor. In the ULN2003, each Darlington pair can sink up to 500mA of current.

Flyback Diodes

Each Darlington pair in the ULN2003 has an integrated flyback diode connected between the collector and emitter. These diodes are used to suppress voltage spikes caused by inductive loads when they are switched off. Without these diodes, the voltage spikes could potentially damage the IC or other components in the circuit.

ULN2003 Electrical Characteristics

The following table summarizes the key electrical characteristics of the ULN2003:

Parameter	Symbol	Min	Typ	Max	Unit
Collector-Emitter Voltage	VCE	–	–	50	V
Collector Current (per channel)	IC	–	–	500	mA
Input Voltage (low)	VIL	–	–	1.5	V
Input Voltage (high)	VIH	2.7	–	–	V
Input Current (per channel)	II	–	–	1.25	mA
Collector-Emitter Saturation Voltage	VCE(sat)	–	1.1	1.3	V
Turn-On Delay Time	tPLH	–	–	0.25	µs
Turn-Off Delay Time	tPHL	–	–	0.25	µs

Applications of the ULN2003

The ULN2003 is widely used in various applications that require driving high current loads. Some common applications include:

1. Relay Driving: The ULN2003 can drive relays directly, allowing microcontrollers or other logic circuits to control high current loads.

2. Stepper Motor Driving: The ULN2003 is often used in stepper motor driver circuits, where it can drive the motor windings directly.

3. LED Display Driving: The ULN2003 can be used to drive LED displays, such as seven-segment displays or dot-matrix displays.

4. Solenoid Driving: The ULN2003 is suitable for driving solenoids, such as those used in electronic locks or valve controls.

5. Automotive Applications: The ULN2003 can be used in automotive applications for controlling various loads, such as lamps, relays, and motors.

ULN2003 Circuit Design Considerations

When designing circuits using the ULN2003, there are several important considerations to keep in mind:

1. Input Logic Compatibility: Ensure that the input logic levels are compatible with the ULN2003. The IC is compatible with TTL and CMOS logic levels.

2. Output Current Limitations: Each output of the ULN2003 can sink up to 500mA of current. If higher currents are required, multiple outputs can be paralleled, or an external transistor can be used.

3. Flyback Diode Selection: Although the ULN2003 has integrated flyback diodes, in some cases, it may be necessary to use external flyback diodes with higher current ratings or faster switching speeds.

4. Heat Dissipation: When driving high current loads, the ULN2003 can generate significant heat. Proper heat dissipation techniques, such as using a heatsink or providing adequate ventilation, should be employed.

5. PCB Layout: To minimize the effects of EMI and noise, proper PCB layout techniques should be followed. This includes minimizing trace lengths, using ground planes, and properly decoupling power supplies.

ULN2003 vs Other Darlington Array ICs

There are several other Darlington array ICs available, such as the ULN2803 and the ULQ2003A. These ICs share many similarities with the ULN2003 but may have different features or specifications.

ULN2803 vs ULN2003

The ULN2803 is an 8-channel Darlington array IC, while the ULN2003 is a 7-channel IC. The ULN2803 has a slightly higher maximum collector current rating of 500mA per channel, compared to the ULN2003’s 500mA rating.

ULQ2003A vs ULN2003

The ULQ2003A is a pin-compatible alternative to the ULN2003 with improved performance. It features a higher maximum collector current rating of 600mA per channel and faster switching speeds.

FAQ

1. What is the maximum collector-emitter voltage of the ULN2003?

The maximum collector-emitter voltage of the ULN2003 is 50V.

2. How much current can each output of the ULN2003 sink?

Each output of the ULN2003 can sink up to 500mA of current.

3. Can the ULN2003 be used to drive a stepper motor directly?

Yes, the ULN2003 is commonly used in stepper motor driver circuits to drive the motor windings directly.

4. Are the inputs of the ULN2003 compatible with both TTL and CMOS logic levels?

Yes, the inputs of the ULN2003 are compatible with both TTL and CMOS logic levels.

5. What is the purpose of the integrated flyback diodes in the ULN2003?

The integrated flyback diodes in the ULN2003 are used to suppress voltage spikes caused by inductive loads when they are switched off, protecting the IC and other components from potential damage.

Conclusion

The ULN2003 is a versatile Darlington transistor array IC that is widely used for driving high current loads in various applications. Its key features, such as high current capability, integrated flyback diodes, and compatibility with various logic levels, make it a popular choice among circuit designers.

When using the ULN2003, it is essential to consider factors such as input logic compatibility, output current limitations, heat dissipation, and proper PCB layout. By understanding the ULN2003’s pinout, electrical characteristics, and application requirements, designers can effectively incorporate this IC into their projects.

As technology continues to advance, the ULN2003 remains a reliable and cost-effective solution for driving high current loads in a wide range of applications, from automotive systems to industrial control and consumer electronics.