74HC74 Dual D Flip-Flop: Datasheet, Pinout, and Circuit Diagram

In digital electronics, the 74HC74 dual D flip-flop is a vital foundational component, serving essential functions across a wide range of applications. The 74HC74 is a dual D-type flip-flop that operates on positive edge-triggered signals. It incorporates separate inputs for data (nD), clock (NCP), as well as set (nSD) and reset (nRD) functions, alongside complementary nQ and nQ outputs. This new technology article manual delves deeply into the 74HC74 dual D flip-flop, delivering valuable knowledge about its datasheet, pin configuration, and flip-flop diagram showcasing its operation.

What is 74HC74?

The 74HC74 is a dual positive edge-triggered D-type flip-flop. It features distinct inputs for data (nD), clock (nCP), set (nSD), and reset (nRD), along with complementary nQ and nQ outputs. These inputs are compatible with standard CMOS outputs and can be used with pullup resistors, making them compatible with LSTTL outputs. Notably, the 74HC74 shares the same pinout as the LS74. And we made a comparative analysis for 74ls vs. 74hc series ICs in our previous article.

This device comprises two D flip-flops with individual Set, Reset, and Clock inputs. Information at a D-input is transferred to the corresponding Q output during the next positive transition of the clock input. Both Q and Q outputs are accessible from each flip-flop, and it's important to note that the Set and Reset inputs operate asynchronously.

74HC74 Pinout

Pin configuration

Pin No.	Name	I/O	Description
1	1 CLR	Input	Channel 1, Clear Input, Active Low
2	1D	Input	Channel 1, Data Input
3	1CLK	Input	Channel 1, Positive edge triggered clock input
4	1 PRE	Input	Channel 1, Preset Input, Active Low
5	1Q	Output	Channel 1, Output
6	1 Q	Output	Channel 1, Inverted Output
7	GND	/	Ground
8	2 Q	Output	Channel 2, Inverted Output
9	2Q	Output	Channel 2, Output
10	2 PRE	Input	Channel 2, Preset Input, Active Low
11	2CLK	Input	Channel 2, Positive edge triggered clock input
12	2D	Input	Channel 2, Data Input
13	2 CLR	Input	Channel 2, Clear Input, Active Low
14	Vcc	/	Positive Supply

74HC74 Technical Specifications

Type	Parameter
Operating Temperature	-55°C~125°C TA
Series	74HC
Voltage - Supply	2V~6V
Number of Pins	14
Current - Output High, Low	5.2mA 5.2mA
Trigger Type	Positive Edge
Clock Edge Trigger Type	Positive Edge
Package / Case	14-SOIC (0.154, 3.90mm Width)
Packaging	Tape & Reel (TR)

74HC74 Features

• Output Drive Strength: Handles 10 LSTTL Loads

• Compatible with CMOS, NMOS, and TTL Interfaces

• Operating Voltage Range: 2.0 to 6.0 V

• Minimal Input Current: Just 1.0 A

• Exceptional Noise Immunity Typical of CMOS Technology

• Complies with JEDEC Standard No. 7A Specifications

• Impressive ESD Performance: HBM 2000 V; Machine Model 200 V

• Integrated Circuit Complexity: Equates to 128 FETs or 32 Equivalent Gates

• Pb−Free Packaging Options Available

• Dual Flip-Flops: The 74HC74 houses two autonomous flip-flops in a single package, granting substantial flexibility in circuit design.

• Positive-Edge Triggering: This IC responds to the rising edge of the clock signal, rendering it well-suited for synchronization and control tasks.

• CMOS Technology: Constructed employing complementary metal-oxide-semiconductor (CMOS) technology, the 74HC74 ensures minimal power consumption and compatibility with an extensive voltage range.

• Broad Operating Voltage Range: It exhibits functionality within a voltage spectrum ranging from 2V to 6V, accommodating diverse power supply configurations.

• High-Speed Operation: The 74HC74 can swiftly toggle states, making it an optimal choice for applications necessitating rapid switching.

74HC74 Circuit Diagram

The IC power source, VDD, spans from 0 to +7V, with detailed information in the datasheet, as depicted in the following snapshot. Additionally, we've incorporated an LED in the output, where the source is constrained to 5V for managing both the supply and DC output voltage. To achieve this, we've harnessed the LM7805 regulator to restrict the LED voltage.

Symbol	Parameter	Value	Unit
Vcc	DC Supply Voltage (Referenced to GND)	-0.5 to + 7.0	V
Vin	DC Input Voltage (Referenced to GND)	-1.5 to VCc* 1.5	V
Vout	DC Output Voltage (Referenced to GND)	- 0.5 to Vcc * 0.5	V
Ijn	DC Input Current, per Pin	±20	mA
lout	DC Output Current, per Pin	±25	mA
lcc	DC Supply Current, Vcc and GND Pins	±50	mA

How does 74HC74 work?

The 74HC74 operates based on the principle of transferring data from its D (Data) input to the corresponding Q (Output) upon the occurrence of a rising edge at the clock input. Let's delve into a detailed explanation of this process:

• Data Input (D): Within the 74HC74, you'll find a Data input labeled as "D." This is where you input the digital data you intend to transfer or store. The data can be a logic HIGH (often represented as '1') or a logic LOW (typically denoted as '0').

• Clock Input (CLK): The clock input, marked as "CLK," plays a pivotal role in the operation. It serves as a timing reference. Data is transferred from the D input to the Q output, specifically when the clock signal transitions from a logic LOW to a logic HIGH, known as the positive-going edge (rising edge).

• Output (Q): The 74HC74 incorporates multiple output pins designated as Q. Each Q output corresponds to a particular D input. For example, input data into D0 will be conveyed to Q0, and this pattern continues for other pairs of D and Q pins.

• Positive-Edge Triggering: The crux of the 74HC74's operation lies in its positive-edge triggering mechanism. When the clock signal transitions from LOW to HIGH (the rising edge), the data present at the D input precisely at that moment is shifted to the corresponding Q output. This transfer occurs nearly instantaneously, ensuring that the output mirrors the state of the D input as soon as the clock rises.

In summary, the 74HC74 functions as a digital flip-flop that executes data transfer from its D input to the corresponding Q output when it detects a rising edge at the clock input. This behavior is pivotal in various digital applications, encompassing tasks like data storage, synchronization, and sequential logic operations. Thanks to its reliability and precise timing, the 74HC74 is a valuable component within digital circuits and systems.

74HC74 Applications

The 74HC74 flip-flops are integral to digital electronic circuits, serving diverse and vital roles. Here, we delve into their applications in detail:

• Counters:

74HC74 flip-flops assume a central role in digital counters. Counters find widespread use in electronics for accurately tracking events, pulses, or data occurrences. Whether it involves counting motor revolutions or measuring signal frequencies, flip-flops within counters enable precise event tallying and monitoring.

• Frequency Dividers:

Frequency dividers hold significance in electronic systems, particularly in signal processing and communication. These dividers employ flip-flops to reduce signal frequencies. This function proves invaluable in applications like scaling clock signals and implementing frequency modulation.

• Shift Registers:

Shift registers serve as pivotal components in data storage and serial data transfer. They harness 74HC74 flip-flops to serially shift data bits, making them versatile for data input and output applications in microcontrollers, LED displays, and communication protocols like UART and SPI.

• Storage Registers:

Storage registers, also called latch registers, rely on flip-flops for temporary data storage. These registers are critical in microprocessor-based systems, where data retention is necessary for processing or transfer. Storage registers facilitate the flow and synchronization of data in intricate digital circuits.

• Signal Processing:

It is used in signal processing circuits to manipulate and control signals effectively.

• Control Systems:

It is vital in control systems where sequential logic and timing are critical.

• Clock Synchronization: 

Precise timing is crucial in digital systems, and the 74HC74's positive-edge triggering capability is perfect for clock synchronization.

74HC74 Equivalent

The 74HC74 flip-flop holds a prominent position in digital electronics, yet several equivalents and alternatives exist, each possessing unique features and specifications. It’s also identical in pinout to the LS74. Below, we delve into some noteworthy substitutes for the 74HC74:

• 74LS74

The 74LS74 emerges as a favored alternative to the 74HC74. It belongs to the Low-Power Schottky (LS) logic family and shares similar flip-flop functionality. However, it operates at distinct voltage levels and may exhibit variations in power consumption. Engineers often opt for the 74LS74 or the 74HC74 based on specific voltage and power prerequisites.

• CD74HC74

The CD74HC74 is another equivalent choice within the HC (High-Speed CMOS) logic family. Like the 74HC74, it delivers dependable flip-flop functionality with low power consumption and extends compatibility to a broad spectrum of digital applications. Designers may favor the CD74HC74 for its harmonious coexistence with other HC series components in their circuit designs.

• CD74HCT74

The CD74HCT74 represents an alternative within the HCT (High-Speed CMOS with TTL-Compatible Inputs) logic family. It encapsulates the advantages of CMOS technology while preserving compatibility with TTL (Transistor-Transistor Logic) inputs. This compatibility assumes paramount importance when interfacing with older TTL-based components or systems.

When navigating the selection among these equivalents and alternatives, engineers contemplate factors such as voltage compatibility, power consumption, and the precise demands of their digital circuits. The availability of multiple options confers flexibility in crafting electronic systems, all the while ensuring compatibility and functionality.

How to Use 74HC74

Incorporating the 74HC74 into your electronic endeavors is a straightforward process. Follow this step-by-step guide:

1. Power Supply Connection

   Ensure that the IC receives power within its specified voltage range, typically 2V to 6V.

2. Clock Signal

   Link the clock signal to the flip-flop's CLK (clock) input. The flip-flop responds to the positive edge of the clock signal.

3. Data Inputs

   Establish connections for your data inputs (D) according to your intended logic levels.

4. Output

   The state of the flip-flop is reflected in the Q outputs. Interconnect these outputs with other components as necessitated by your project.

5. Reset (Optional)

   Should the need arise, utilize the reset (R) input of the 74HC74 to clear the flip-flop.

74HC74 Datasheet

Download 74HC74 Datasheet PDF

Conclusion

Within the realm of electronics, the 74HC74 holds a position of trust and versatility as an integrated circuit. Its dual flip-flop configuration, positive-edge triggering capability, and adaptability to diverse voltage ranges serve as a fundamental component in digital circuitry. Whether you're a seasoned engineer or an electronics enthusiast, gaining insight into the 74HC74 can unlock opportunities for a broad spectrum of innovative projects and applications.

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