ULN2004A

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ULN2004A Application Field and Working Principle

The ULN2004A is a monolithic high voltage and high current Darlington array. It is comprised of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. It is also known for its high-voltage and high-current transfer capacity, making it suitable for many applications.

The ULN2004A is most commonly used in signal relays, inductive loads, switching regulators, LED display devices, battery chargers, power supplies, and industrial control systems. It is also used as a buffer to drive multiple loads with a single driver. The ULN2004A provides a large amount of current up to 500mA per output with a supply voltage ranging from 5V to 45V.

Features

• High-voltage outputs with common-cathode clamp diodes for switching inductive loads
• High-current transfer capacity for multiple loads
• Output current up to 500mA
• Voltage supply range from 5V to 45V
• On-resistance of 0.2Ω

Working Principle

The ULN2004A is essentially a collection of seven Darlington array circuits, with each circuit consisting of one input and two outputs. Each circuit is made up of a pair of NPN transistors in a Darlington configuration, as well as a pair of clamp diodes to protect the transistors from over-voltage conditions.

When the input to a given circuit is driven high, current flows through the two transistors in the Darlington circuit and the output of the circuit switches on. This causes current to flow through the load, producing the desired effect. When the input is driven low, the circuit switches off and the current through the load is interrupted.

Pinouts

The ULN2004A has a total of 16 pins, including 8 inputs, 8 outputs, and 2 power pins. The following diagram shows the basic pinouts of the device.

Conclusion

In conclusion, the ULN2004A is a popular monolithic high voltage and high current Darlington array. It is widely used in signal relays, inductive loads, LED display devices, and other applications that require high voltage and current transfer. It is also an ideal buffer for driving multiple loads with a single driver. The ULN2004A comes with 8 inputs, 8 outputs, and 2 power pins.

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