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74LS74 Dual D Flip-Flop

[Click the image to enlarge it]

74LS74A flip-flop IC utilizes the Schottky TTL circuitry to produce high-speed D-type flip-flops. Each flip-flop has individual clear and set inputs, and also complementary Q and Q`(bar) outputs.

 

74LS74 Pin Configuration:

Pin Number

Pin Symbol

Name

Description

5,9

1Q / 2Q

Output

Output Pin of the Flip Flop

6,8

1Q’(bar) / 2Q’(bar)

Complementary Output

Inverted output pin of Flip Flop

3, 11

1CLK / 2CLK

Clock Input Pin

These pins must be provided with clock pulse for the flip flop

1,13

1CLR (bar) / 2CLR (bar)

Clear Data

Resets the flip flop by clearing its memory

2,12

1D /2D

Data Input Pin

Input pin of the Flip Flop

4, 10

1PRE (bar) / 2PRE (bar)

PRE Input

Another Input pin for Flip Flop. Also referred to as a set pin

7

Vss

Ground

Connected to the ground of the system

14

Vdd/Vcc

Supply Voltage

Powers the IC typically with 5V

 

Features of 74LS74:

  • Dual D Flip Flop Package IC
  • Operating Voltage: 2V to 15V
  • Propagation Delay: 40nS
  • Minimum High-Level Input Voltage: 2 V
  • Maximum Low-Level Input Voltage: 0.8V
  • Operating Temperature: 0 to 70°C
  • High-Level Output Current: 8mA
  • Available in 14-pin SO-14, SOT42 packages

Note:  Complete Technical Details can be found at the 74LS74 datasheet given at the end of this page.

 

74LS74 Equivalents: 74LVC2G80, HEF40312B

 

How to use 74LS74:

Using a Flip-Flop is pretty straight forward. Simply power the IC using the Vcc and GND pin. As told early each flip-flop operates independently, just connect the input signals 2 and 3 for using the 1st flip-flop and you will get the output at pins 5 and 6. The pin 3 should be provided with a clock source normally a PWM signal from an MCU or 555 timers is used. The pin can be used to clear the data and reset the flip flop by making it high. The complete working of the Flip flop can be understood by taking at the function table below. The symbol “X” indicates don’t care and the up-arrow indicates the rising edge of the signal.

 

INPUTS

OUTPUTS

PRE (bar)

CLR (bar)

CLK

D

Q

Q (bar)

L

H

X

X

H

L

H

L

X

X

L

H

L

L

X

X

H

H

H

H

 

H

H

L

H

H

 

L

L

H

H

H

L

X

Q0

Q0 (bar)

 

You can also simulate the IC to check if it would work as desired. Here I have used logic state and logic bits to view if the IC functions as it is supposed to, but you can replace them with actual circuitry of your application to check if it would suit your need. The gif file shown below can be verified with the truth table above to make sure that the IC works as desired.

 

74LS74 Circuit Working

 

Applications of 74LS74

  • Used as Shift Registers
  • Memory/Control Registers
  • Buffer Circuits
  • Sampling Circuits
  • Latching devices

 

2D Model of 74LS74 (CDIP):

Dimensions for the 74LS74 IC is given below. These dimensions are for the CDIP package. If you are using different package IC please refer to the 74LS74 datasheet.

74LS74 Dimensions

Component Datasheet

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