Schmitt Trigger-Inverting Schmitt Trigger using OP-Amp in English
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Inverting Schmitt TriggerComparator circuit with
Inverting Schmitt Trigger
Comparator circuit with positive feedback are called as Schmitt trigger
They have two stable states(+Vsat and –Vsat) (Bi-stable circuit)
It is a square wave generator
Hysteresis is found in Schmitt trigger circuit
Definition
The output voltage changes its states when ever input voltage exceeds certain voltage level ,upper threshold voltage VUT and lower threshold voltage VLT
Types of Schmitt Trigger
Inverting Schmitt Trigger
Non inverting Schmitt Trigger
In inverting op-amp
Vo = -AOLVin
In inverting Schmitt trigger
Vo = AOL(Vf - Vin) = AOLVd
Vo =AOL(-Vin + Vf)
The voltage across R1 is feedback voltage Vf
Feedback voltage depends on value and polarity of output voltage
Upper threshold voltage VUT
The value of Vin that forces the output to make the transition from +Vsat to –Vsat
When Vout= +Vsat
Vf = VUT
VUT =(+"Vsat X R1" )/("R1" +"R2" )
Lower threshold voltage VLT
The value of Vin that forces the output to make the transition from -Vsat to +Vsat
When Vout= -Vsat
Vf = VLT
VLT =(−"Vsat X R1" )/("R1" +"R2" )
Hysteresis
Hysteresis occurs when positive feedback is used in comparator
Due to hysteresis the comparator output makes transition at different points when comparator changes its state from low to high and high to low
Effect of Hysteresis
Noise immunity is improved
Response time reduces
Sensitivity of circuit reduces as the circuit does not respond to input voltage changes in dead zone or in hysteresis range
False triggering due to noise is reduced
Advantages of Schmitt trigger
Due to positive feedback, the speed of response is increased
Due to hysteresis the problem of relay chattering is reduced as the Schmitt trigger does not change its output in hysteresis range
By adjusting the VUT and VLT the duty cycle of square wave can be adjusted
The monolithic Schmitt triggers are uncompensated, therefore they have high speed of response
Disadvangtages of Schmitt trigger
Sensitivity of Schmitt trigger decreases with increase in hysteresis because the circuit does not respond in hysteresis range
To overcome this problem
If value of Vin increases then VUT is reference voltage i.e. the output will not change at VLT
If value of Vin decreases then VLT is reference voltage i.e. the output will not change at VUT
Comparator circuit with positive feedback are called as Schmitt trigger
They have two stable states(+Vsat and –Vsat) (Bi-stable circuit)
It is a square wave generator
Hysteresis is found in Schmitt trigger circuit
Definition
The output voltage changes its states when ever input voltage exceeds certain voltage level ,upper threshold voltage VUT and lower threshold voltage VLT
Types of Schmitt Trigger
Inverting Schmitt Trigger
Non inverting Schmitt Trigger
In inverting op-amp
Vo = -AOLVin
In inverting Schmitt trigger
Vo = AOL(Vf - Vin) = AOLVd
Vo =AOL(-Vin + Vf)
The voltage across R1 is feedback voltage Vf
Feedback voltage depends on value and polarity of output voltage
Upper threshold voltage VUT
The value of Vin that forces the output to make the transition from +Vsat to –Vsat
When Vout= +Vsat
Vf = VUT
VUT =(+"Vsat X R1" )/("R1" +"R2" )
Lower threshold voltage VLT
The value of Vin that forces the output to make the transition from -Vsat to +Vsat
When Vout= -Vsat
Vf = VLT
VLT =(−"Vsat X R1" )/("R1" +"R2" )
Hysteresis
Hysteresis occurs when positive feedback is used in comparator
Due to hysteresis the comparator output makes transition at different points when comparator changes its state from low to high and high to low
Effect of Hysteresis
Noise immunity is improved
Response time reduces
Sensitivity of circuit reduces as the circuit does not respond to input voltage changes in dead zone or in hysteresis range
False triggering due to noise is reduced
Advantages of Schmitt trigger
Due to positive feedback, the speed of response is increased
Due to hysteresis the problem of relay chattering is reduced as the Schmitt trigger does not change its output in hysteresis range
By adjusting the VUT and VLT the duty cycle of square wave can be adjusted
The monolithic Schmitt triggers are uncompensated, therefore they have high speed of response
Disadvangtages of Schmitt trigger
Sensitivity of Schmitt trigger decreases with increase in hysteresis because the circuit does not respond in hysteresis range
To overcome this problem
If value of Vin increases then VUT is reference voltage i.e. the output will not change at VLT
If value of Vin decreases then VLT is reference voltage i.e. the output will not change at VUT
5 سال پیش
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