ULN2803A Darlington Transistor Specifications, Characteristics, Working Principle and More
24 January 2024
Ⅲ. Characteristics of ULN2803A
Ⅳ. Schematic diagram of ULN2803A
Ⅶ. Application circuit of ULN2803A
Ⅷ. How to install ULN2803A through circuit board layout?
ULN2803A is a commonly used integrated circuit chip that is a high-current and high-voltage relay array driver. It is an 8-bit NPN integrated transistor array that can be used for high-current loads such as LED strips, displays, stepper motors, and drive relays. Below we will introduce the characteristics, specifications, working principle and application scenarios of ULN2803A in detail.
ULN2803A is a Darlington transistor matrix with NPN transistor polarity. The ULN2803A contains eight Darlington transistors with a common emitter and integrated suppression diodes for inductive loads. Each Darlington has a peak load current rating of 600 mA (500 mA continuous) and can withstand at least 50 volts in the off state. Outputs can be paralleled for higher current capabilities. The ULN2803A has 2.7 kilohm input resistors for 5V TTL and CMOS. The device is available as an 18-lead plastic DIP in the form of copper leads and has convenient input and reverse output pins to simplify board layout.
Alternatives and equivalents:
• ULN2802A
• ULQ2803A
• It has a power rating of 2.25 W.
• It dissipates 2250 mW of power.
• It adopts through-hole mounting method.
• Its continuous collector current is 500 mA.
• Its operating temperature is -20°C to 85°C.
• Its length is 23.24 mm, width is 7.1mm and height is 3.68mm.
• ULN2803A is manufactured by STMicroelectronics.
• ULN2803A belongs to the category of Darlington transistors.
• ULN2803A has 18 pins and is available in PDIP-18 package and tube packaging.
ULN2803A has the following features:
• High voltage output: The ULN2803A is capable of driving higher voltage loads, typically operating in the 5V to 50V range.
• Low power consumption: When the output is at a high level, the ULN2803A's static power consumption is relatively low, helping to reduce the energy consumption of the entire system.
• Internal cancellation resistor: The ULN2803A's output pins contain internal cancellation resistors to simplify circuit design for loads connected to the power supply.
• Compatible with TTL and CMOS logic levels: The input is compatible with TTL and CMOS logic levels, so it can be easily interfaced with microcontrollers or other logic devices in digital circuits.
• Built-in protection diode: ULN2803A has an internal protection diode to prevent the inductive load from generating reverse voltage when the power is cut off. This helps improve reliability and protect other components.
• High current output: It has eight open-drain output channels, each channel can provide a maximum current of 500mA. This makes it suitable for controlling a variety of electromagnetic loads such as solenoid valves, relays and stepper motors.
• Input and output isolation: The input and output of the ULN2803A are electrically isolated, which means that the input signal is isolated from the output load by a transistor, helping to prevent potential electrical interference.
ULN2803A is an integrated high voltage, high current Darlington driver. It consists of eight independent Darlington pairs, each capable of handling 500mA of current and 50V of voltage. The driver works by utilizing the Darlington pairs to amplify the input signal to control higher current and higher voltage loads. When an input signal is applied to the ULN2803A's input pins, the corresponding output pins provide sufficient current and voltage to drive various loads, such as relays, motors, light bulbs, etc. The ULN2803A's output pins are also capable of handling 500mA of current and 50V of voltage. In addition, the internal structure of the ULN2803A excels in protecting the isolation between the inputs and outputs, while also providing high current amplification and low saturation voltage drop, giving it excellent performance in controlling high current loads.
ULN2803A is commonly used in the following areas:
The first is programmable load sharing. When we have a high-power load and a low-power load, we can parallel multiple arrays together to drive a high-power load.
The second is where you need to use CONTROL UNIT's LOGIC to control inductive loads. In the ULN2803A, the Darlington array functions as a set of eight independent switches, capable of being triggered ON and OFF individually. Each of these switches can drive high-power loads and receive logic signals from the control unit.
Finally is where multiple loads are driven. The ULN2803A has the capability to concurrently operate eight loads. While achieving a similar outcome is possible with MOSFETs or transistors, incorporating multiple devices on the board may lead to complications. Therefore, by using ULN2803A, circuit design can be simplified and reliability improved.
The figure above shows the circuit connection diagram using 8-way Darlington inverting driver ULN2803A (IC1) to drive 8 export relays. The relay used is a 24V specification with larger contact power, and the corresponding control voltage is 0V or 5V. In order to achieve level conversion and eliminate interference caused by sensors and switching actions, we use two DIP packaged photoelectric couplers TLP521-4 (IC2, IC3) at the control port PCD-PC70 in the middle of the figure below.
As can be seen from the above figure, ICI has internally provided the collector of each Darlington transistor (i.e., the collector of the transistor on the right side in Figure 3). In the figure below, it is the output terminal 11 to 18 of each inverting driver. ) is equipped with a diode. Since the collector of the Darlington transistor is an open-circuit output, the current output of the Darlington transistor will have a path only when the load element relay coil is connected between the load power supply 24V and the collector. By connecting the ⑩ pin of the integrated circuit IC1 to the load power supply 24V, the internal freewheeling protection diode will automatically be connected in parallel with the relay coil, thereby achieving protection. Therefore, relay coils connected externally to the integrated circuit do not need to be reconnected with protective diodes.
First of all, in order to meet the requirements of the circuit design, we need to determine the mounting location of ULN2803A and reserve appropriate space for it. Since the ULN2803A features input-reverse output pins, we must pay special attention to the configuration of the pins during board layout. The input pins and output pins need to be positioned relative to each other on the board to facilitate connections to other circuit components.
During the layout process, we need to make sure that the spacing between the ULN2803A and other circuit components is moderate. This facilitates soldering as well as wiring. Simultaneously, in order to mitigate interference and minimize resistance, it is essential to ensure that the connection paths to other components are kept as brief as possible. To ensure the proper operation of the ULN2803A, we need to provide it with a stable power supply and reliable grounding. When laying out the ULN2803A, we need to give full consideration to the width and length of the power and ground wires to reduce resistance and prevent interference. Since ULN2803A will emit a certain amount of heat during operation, we need to design heat dissipation at its mounting location. We can enhance the heat dissipation effect by adding heat sinks or reserving space on the PCB for heat dissipation.
Frequently Asked Questions
1. What is the minimum voltage for ULN2803?
The minimum rating for the ULN2803A is based on the ESD diode integrated, and that would limit the minimum voltage to -0.3V.
2. What is the difference between ULN2803 and 2003?
ULN2803 - This is identical to the ULN2003, except that it has 18 pins and 8 channels, instead of 16 pins and 7 channels. UDN2981 - This is much like the ULN2803, however, it acts as a high side driver, pulling the outputs up to Vs, rather than down to ground.
3. Why we use ULN2803?
In summary, the ULN2803 is used in driving a relay primarily to increase the current limit in the relays. By providing high-current drive capability, it enables the relay to switch higher current loads without exceeding its maximum rated current.
4. What does ULN2803A do?
The ULN2803A 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.
5. What is the spec of ULN2803?
The ULN2803 is high-voltage high-current Darlington transistor arrays each containing eight open collector common emitter pairs. Each pair is rated at 500mA. Suppression diodes are included for inductive load driving, the inputs and outputs are pinned in opposition to simplify board layout.
