# Chapter 6 - Schmitt Trigger Circuits and Voltage Comparators¶

## Example E1 - Pg 179¶

In [1]:
#Caption:Determine schmitt trigger circuit components for designing it
u=5.#Upper trigger point voltage(in volts)
Vbe=0.7#Base emitter voltage(in volts)
I=2.#Collector current(in mA)
hfe=100.
Vcc=12.#Collector voltage(in volt)
Vce=0.2#Saturated collector emitter voltage(in volts)
Ve=u-Vbe
Re=Ve/I
Rc=(Vcc-Ve-Vce)/I
i=I/10.
R2=u/i
Ib2=I/hfe
I2=u/i
It=Ib2+i
r=(Vcc-u)/It
R1=r-Rc
print '%s %.2f %s %.2f %s %.f %s %.1f' %('Circuit components are \nRe(in kilo ohm)=',Re,'\nRc2(in kilo ohm)=',Rc,'\nR2(in kilo ohm)=',R2,'\nR1(in kilo ohm)=',R1)

Circuit components are
Re(in kilo ohm)= 2.15
Rc2(in kilo ohm)= 3.75
R2(in kilo ohm)= 25
R1(in kilo ohm)= 28.1


## Example E2 - Pg 181¶

In [3]:
#Caption:Find circuit components for designing a schmitt trigger circuit
u=5.#Upper trigger point voltage(in volts)
Vbe=0.7#Base emitter voltage(in volts)
I=2.#Collector current(in mA)
hfe=100.
Vcc=12.#Collector voltage(in volt)
Vce=0.2#Saturated collector emitter voltage(in volts)
l=3.#Lower trigger point voltage(in volts)
Ve=u-Vbe
Re=2.2
R1=23.6
Rc=(Vcc-Ve-Vce)/I
R2=22
i=I/10.
Ib2=I/hfe
I2=u/i
It=Ib2+i
r=(Vcc-u)/It
I1=l/R2
Ie=(l-Vbe)/Re
Rc1=Vcc-(I1*(r+R2))/Ie

print '%s %.1f %s %.2f %s %.f %s %.1f' %('Circuit components are \nRe(in kilo ohm)=',Re,'\nRc1(in kilo ohm)=',Rc1,'\nR2(in kilo ohm)=',R2,'\nR1(in kilo ohm)=',R1)

Circuit components are
Re(in kilo ohm)= 2.2
Rc1(in kilo ohm)= 4.98
R2(in kilo ohm)= 22
R1(in kilo ohm)= 23.6


## Example E3 - Pg 183¶

In [4]:
#Caption:Determine Largest speed up capacitance
f=1.#Frequency(in Mhz)
R1=22.#Resistance(in kilo ohm)
R2=22.#Resistance(in kilo ohm)
Rc1=4.7#Resistance(in kilo ohm)
R=R1*(Rc1+R2)/(R1+Rc1+R2)
t=1./f
C=t*1000./(2.3*R)
print '%s %.f' %('Required Capacitance(in pF)=',C)

Required Capacitance(in pF)= 36


## Example E4 - Pg 186¶

In [5]:
#Caption:Calculate R1,R2 and Actual UTP and LTP
u=3.#Upper trigger voltage(in volts)
Ib=500.#Max base current(in nA)
Vcc=15.#Collector voltage(in volts)
i=Ib*0.1
R2=u*1000./i
I=u/R2
Vo=Vcc-1
Vr1=Vo-u
R1=Vr1/I
utp=Vo*R2/(R1+R2)
ltp=-utp
print '%s %.f %s %.f %s %.1f %s %.1f' %('Circuit components \nR1(in kilo ohm)=',R1,'\nR2(in kilo ohm)=',R2,'\nactual UTP(in volts)=',utp,'\nactual LTP(in volts)=',ltp)

#utp and ltp values are corrected

Circuit components
R1(in kilo ohm)= 220
R2(in kilo ohm)= 60
actual UTP(in volts)= 3.0
actual LTP(in volts)= -3.0


## Example E5 - Pg 189¶

In [6]:
#Caption:Design Schmitt circuit components R1,R2,R3,R4 and R5
u=3.#Upper trigger voltage(in volts)
Ib=500.#Max base current(in nA)
Vf=0.7#Forward diode voltage(in volts)
Vk1=-2.#Voltage(in volts)
Vcc=15.#Collector voltage(in volts)
Vk2=-Vk1
i=Ib*0.1
R2=u*1000./i
I=u/R2
Vo=Vcc-1
Vr1=Vo-u
R1=Vr1/I
I4=100.*i
Va1=Vk1+Vf
Vee=-Vcc
V4=Va1-Vee
R4=V4*1000./I4
Va2=Vk2+Vf
V5=Va2-Va1
R5=V5*1000./I4
R3=(Vcc-Va2)*1000./I4
print '%s %.f %s %.f %s %.2f %s %.2f %s %.f' %('R1(in kilo ohm)=',R1,'\nR2(in kilo ohm)=',R2,'\nR3(in kilo ohm)=',R3,'\nR4(in kilo ohm)=',R4,'\nR5(in kilo ohm)=',R5)

R1(in kilo ohm)= 220
R2(in kilo ohm)= 60
R3(in kilo ohm)= 2.46
R4(in kilo ohm)= 2.74
R5(in kilo ohm)= 1


## Example E6 - Pg 192¶

In [7]:
#Caption:Design a non inverting schmitt trigger circuit
Vcc=15.#Collector voltage(in volts)
u=2.#Upper trigger point(in volts)
Ib=500.#Base current(in nA)
I2=Ib*0.1
Vo=Vcc-1
R2=Vo*1000./I2
i=Vo*1000./R2
R1=u*1000./i
print '%s %.1f %s %.f' %('Circuit components \nR1(in kilo ohm)=',R1,'\nR2(in kilo ohm)=',R2)

Circuit components
R1(in kilo ohm)= 40.0
R2(in kilo ohm)= 280