74LS74 Dual D Flip-Flop

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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 NumberPin SymbolNameDescription
5,91Q / 2QOutputOutput Pin of the Flip Flop
6,81Q’(bar) / 2Q’(bar)Complementary OutputInverted output pin of Flip Flop
3, 111CLK / 2CLKClock Input PinThese pins must be provided with clock pulse for the flip flop
1,131CLR (bar) / 2CLR (bar)Clear DataResets the flip flop by clearing its memory
2,121D /2DData Input PinInput pin of the Flip Flop
4, 101PRE (bar) / 2PRE (bar)PRE InputAnother Input pin for Flip Flop. Also referred to as a set pin
7VssGroundConnected to the ground of the system
14Vdd/VccSupply VoltagePowers 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.

PRE (bar)CLR (bar)CLKDQQ (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

Farees Ahmed

The aim of this blog is to serve as a quick reference guide for the Curious. Appreciate your feedback and comments !