3 rd sem electrical

Group:- 6 Vaibhav Bhavin Manav Kaushal Rajesh Hitesh Mehul

Overview Comparator 1. Non-inverting 2. inverting Practical comparator Schmitt trigger Zero crossing detector

Comparator Basic function of a comparator The basic function of compartor is to compare the voltage applied at one of its inputs to that applied at its other input and to produce and output voltage which is either Voh or Vol. let the voltage applied at the non-inverting input be denoted by Vp and that applied at the inverting terminal be Vn.

Comparator symbol and ideal voltage transfer characteristics If A 0 is large, practical response can be approximated as : V IN > 0  V + > V -  V OUT = +V SAT V IN < 0  V + < V -  V OUT = -V SAT

Type of comparator There are two type of comparator 1. Non-inverting comparator 2. Inverting comparator

Simple Non-inverting Comparator Intro to Mechatronic Design, Fig , p. 246 Intro to Mechatronic Design, Fig , p. 247

Non- inverting The schematic diagram of a non-inverting comparator is as shown in fig A positive dc reference voltage is applied to the inverting terminal (-) and an ac sinusoidal signal is applied to the non-inverting (+) terminal As the signal is connected to the non- inverting terminal, This comparator is called as non-inverting comparator.

Inverting Comparator

Inverting comparator The schematic diagram of an inverting comparator is as shown in fig. and the relevant waveforms are shown in fig. Note that the reference voltage Vref has now been applied to the non-inverting (+)terminal and the voltage is applied to the inverting (-) terminal.

Input and Output waveforms of inverting comparator

Window comparator The window detector circuit using two comparator is as shown in fig. The window detector circuit is used for detecting whether an unknown voltage Vin falls within a specified voltage band called window. A high output voltage indicates that the input voltage is within the window whereas a low output voltage indicates that the input voltage is out of the window.

Circuit of Window detector

Operation of the circuit The output voltage is obtained at the common collector terminal of the two transistors. If Vin is between the two reference voltage,then the output of the both the comparator will be low. So both the transistor will remain off state. So the collector voltage =+Vcc

Input and output voltage waveforms for a window detector

Schmitt Trigger The Schmitt trigger is an op-amp comparator circuit featuring hysteresis. The inverting variety is the most commonly used.

Schmitt Trigger The inverting schmitt trigger circuit is as shown in fig. This schmitt trigger circuit is basically an inverting comparator with positive or nagative feedback introduced therefore it is called as regenerative comparator. Input voltage is applied to the inverting input terminal.

Schmitt Trigger Analysis But, Switching occurs when:

Waveform for inverting schmitt trigger

Zero crossing detector Zero crossing detector is shown in fig. as you can see, Zero Crossing detector is nothing but the comparator Circuit with a zero reference voltage applied to the non inverting terminal. The zero crossing detector thus switches its output form one state to the other every time when the input voltage crosses the zero. The zero crossing detector is also known as a sine wave to square wave converter.

Zero crossing detector

Input and output voltage waveforms

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