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comparator instuments
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Learning Objectives
Explain the basic comparator action considering inputs to an op-amp
Construct an inverting or non-inverting comparator using a comparator with open collector output
Explain the concept of hysteresis to avoid ‘chatter’ around a reference level
Mechatronics Concept Map
Controller(Hardware & Software)
System toControl
Sensor
SignalConditioning
PowerInterface
Actuator
UserInterface
PowerSource
BJ Furman 22JAN11
ME 106ME 154ME 157ME 195
ME 120ME 297A
ME 106ME 120
ME 106ME 190ME 187
ME 110ME 136ME 154ME 157
ME 182ME 189ME 195
ME 106ME 120
ME 106
INTEGRATION
The Comparator A specially designed op-amp,
optimized to switch Vout fast If V+ > V-, then Vout Vs If V- > V+, then Vout 0 V
But usually output is ‘open collector’ Can pull low, but… Needs external resistor (pull-up) to go
high
Intro to Mechatronic Design, Fig. 11.17, p. 245
Intro to Mechatronic Design, Fig. 11.18, p. 245
Typical op-amp output stage and some comparators (Push-Pull (Totem Pole))
Open collector output stage (typical of most comparators, such as LM339)
http
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Simple Non-inverting Comparator
Intro to Mechatronic Design, Fig. 11.19, p. 246
Intro to Mechatronic Design, Fig. 11.20, p. 247
Inverting Comparator with Hysteresis
Add hysteresis (i.e., a change in Vref that depends on Vout by feeding back to the non-inverting terminal When the input voltage rises to the
threshold, the threshold drops to a lower value
When the input voltage drops to the threshold, the threshold is raised to a higher value
See equations and method in the Intro to Mechatronics text, pp. 247-248
http://www.ermicro.com/blog/wp-content/uploads/2010/03/comp_10.jpg
Window comparator
http://www.sparkfun.com/datasheets/Widgets/Window%20Comparator-v15.pdf
Two comparators with two Vrefs: VrefHigh and VrefLow One non-inverting (IC1A) One inverting (IC1B)