EELE 262 – Logic Circuits Lab
Lab #3 – DC Operating Conditions Under Different Load Types
Objective
The objective of this lab is to become familiar with the DC behavior of 74LS logic gates when driving different types
of loads.
Outcomes
After completing this lab you should be able to:
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Read and understand the DC specifications listed in a datasheet for a 74LS gate.
Measure the DC operating conditions of a 74LS gate.
Observe the impact of loading on the DC operating conditions.
Pre-Lab
A) Create the following table in your lab notebook and fill in the DC specifications from the 74LS04 Inverter
datasheet. You can either redraw this table or print out another copy of this page and cut/tape this table in
your lab notebook. The information in the datasheet is found in the Recommended Operating Conditions
and Electrical Characteristics tables. Note that the Noise Margins are calculated by you.
Lab Work & Demonstration
1) Driving a 74LS Gate as a Load - Breadboard the following circuit and measure the DC operating conditions
of the 74LS04 inverter when driving another 74LS gate (e.g., another 74LS04 inverter) as the load.
Remember that you need to provide power and ground to both inverters. You are going to drive in both a
logic 0 and a logic 1 as the inputs and measure the voltages and currents indicated in the circuit diagram
provided. You will drive in the input logic states by connecting the input to the power or ground rails of your
breadboard. A table is provided at the end of this handout for reference that you can copy into your lab
notebook and fill in as you take the measurements. The parameters ICCH and ICCL represent the power
supply current when the gate is driving an output 1 and 0 respectively.
TA will check off and verify you are taking the measurements correctly.
EELE 262 – Logic Circuits Lab
Lab #3 – DC Operating Conditions …
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2) Driving a Resistive Load – Now breadboard the following circuit and repeat the DC measurements.
3) Driving an LED (VIN=0= ON) – Now breadboard the following circuit and repeat the DC measurements. In
this circuit the inverter is sourcing current to turn the LED on.
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EELE 262 – Logic Circuits Lab
Lab #3 – DC Operating Conditions …
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4) Driving an LED (VIN=1= ON) – Now breadboard the following circuit and repeat the DC measurements. In
this circuit the inverter is sinking current to turn the LED on so IO will be negative.
5) Comments – In your lab notebook, comment on the difference in the DC operating conditions between the
loading types. What values changed? Did you violate any specifications when driving any of the loads?
After writing down your comments, show your measurements to the lab instructor and explain your
comments.
TA will check off and check your table
Lab Grading
Pre-Lab
___________ / 10
Lab Demo (step 1)
Lab Demo (step 5)
___________ / 30
___________ / 60
Total
___________ / 100
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