The **ULQ2001** and **ULQ2003** (often part of the ULQ200x series) are high-voltage, high-current **Darlington transistor arrays**. These components are designed to interface between low-level logic circuits (like microcontrollers) and high-power peripherals such as motors, solenoids, or lamps. --- ## 1. Technical Specifications Overview The series is built using NPN Darlington pairs, which allow for high current gain. Below are the typical characteristics for the ULQ2001/08 series: | Feature | Specification (Typical) | |:---|:---| | **Collector-Emitter Voltage** | Up to 50V | | **Output Current** | 500mA per channel (Continuous) | | **Channels** | 7 Darlington pairs | | **Input Logic Compatibility** | TTL, 5V CMOS (ULQ2003) | | **Clamp Diodes** | Integrated for Inductive Load transients | | **Package Types** | DIP-16, SO-16, TSSOP-16 | --- ## 2. Internal Architecture Each of the seven channels consists of a Darlington pair. A Darlington pair uses two transistors where the emitter of the first is connected to the base of the second, multiplying the overall current gain ($\beta$). ### Key Components per Channel: * **Input Resistor:** Limits the base current. * **Darlington Pair:** Provides the high-current switching capability. * **Suppression (Flyback) Diode:** Connected between the output and the COM pin to protect the transistors from voltage spikes when driving inductive loads (like relays). --- ## 3. Pin Configuration (16-Pin Layout) | Pin No. | Name | Description | |:---:|:---|:---| | 1 - 7 | **IN 1-7** | Input pins (connected to MCU/Logic) | | 8 | **GND** | Common Ground | | 9 | **COM** | Common Cathode (for flyback diodes) | | 10 - 16 | **OUT 7-1** | Collector outputs (inverted from inputs) | --- ## 4. Operational Principle The ULQ2001 series operates as a **Low-Side Switch**. 1. When a **HIGH** signal (e.g., 5V) is applied to an input pin, the corresponding Darlington pair saturates (turns ON). 2. The output pin is pulled to **Ground**, allowing current to flow from the power source through the load and into the IC. 3. When the input is **LOW**, the transistors turn OFF, and the load is disconnected from the ground. --- ## 5. Typical Applications * **Relay Drivers:** Activating mechanical relays from a microcontroller. * **Stepper Motor Control:** Driving the phases of a unipolar stepper motor. * **LED Displays:** Driving high-power LED segments or arrays. * **Solenoids:** Controlling industrial valves or actuators. --- ## 6. Comparison Table: ULQ2001 vs. ULQ2003 | Model | Input Characteristics | Best Use Case | |:---|:---|:---| | **ULQ2001** | General Purpose (No input resistor) | Custom bias requirements | | **ULQ2003** | 2.7kΩ series resistor | Direct interface with 5V TTL/CMOS | ---