Chapter 11: Voltage Regulators

example 11.1, Page No. 414

In [7]:
# op-amp series voltage regulator design

import math
#Variable declaration
Vin_min = 18-3             # min input voltage specification
Vin_max = 18+3             # max input voltage specification
Vout = 9                   # output voltage specification
Iout_min = 10*10**-3       # min output current specification
Iout_max = 50*10**-3       # max output current specification
Vz = 5.6                   # zener breakdown voltage
Pzmax = 0.5                # Maximum power dissipation in zener

#Calculations
R1 = 10*10**3              # assumed
R2 = R1/((Vout/Vz)-1)
R3 = (Vin_min-Vz)/Iout_max
Iz = (Vin_max-Vz)/R3
Pd = Iz*Vz
beta = 30                  # assumed
Ib = Iout_max/(beta+1)

#Result
print("Element values for designed circuit are as follows:\nR1 = %d k-ohm\nR2 = %.2f k-ohm"%(R1/1000,R2/1000))
print("R3 = %.3f k-ohm\nIB = %.2f mA"%(R3/1000,Ib*1000))
#Answer for R3 is wrong in the book

Element values for designed circuit are as follows:
R1 = 10 k-ohm
R2 = 16.47 k-ohm
R3 = 0.188 k-ohm
IB = 1.61 mA

example 11.2, Page No. 420

In [12]:
# Regulator using IC 723

import math
#Variable declaration
Vout = 5                     # Required output voltage
Iout = 100*10**-3            # Required output current
Vin_min = 15-(0.2*15)        # Min input voltage
Vin_max = 15+(0.2*15)        # Max input voltage
Isc = 150*10**-3             # Short circuit current requirement
Vsense = 0.7                 # short circuit voltage
Vref = 7.15                  # reference votage for IC 723
Id = 1*10**-3                # potential divider current


#Calculation
Rsc = Vsense/Isc
R1 = (Vref-Vout)/Id
R1std = 2.2*10**3 
R2 = R1std/((Vref/Vout)-1)
R2std = 5.1*10**3 
R3 = R1std*R2std/(R1std+R2std)
R3std = 1.5*10**3 

#Result
print("R1 = %.3f k-ohm\t We use %.1f k-ohm as standard resistor."%(R1/1000,R1std/1000))
print("R2 = %.3f k-ohm\t We use %.1f k-ohm as standard resistor."%(R2/1000,R2std/1000))
print("R3 = %.3f k-ohm\t We use %.1f k-ohm as standard resistor."%(math.floor((R3/1000)*1000)/1000,R3std/1000))

R1 = 2.150 k-ohm	 We use 2.2 k-ohm as standard resistor.
R2 = 5.116 k-ohm	 We use 5.1 k-ohm as standard resistor.
R3 = 1.536 k-ohm	 We use 1.5 k-ohm as standard resistor.

example 11.3, Page No. 421

In [24]:
# Ic 723 based positive voltage regulator

import math
#Variable declaration
Vout = 12.0               # output voltage
Il = 500*10**-3           # load current
Isc = 600*10**-3          # short circuit current
Vref = 7.0                # IC 723 reference voltage 
Vsense = 0.6              # voltage at short circuit

#Calculation
R1 = 4.7*10**3            # assumed
R2 = Vref*R1/(Vout-Vref)
R2std = 6.8*10**3 
Rsc = Vsense/Isc
R3 = R2std*R1/(R2std+R1)
Psc = Isc**2*Rsc*1000
I = Vout/(R1+R2std)
I= math.floor(I*10**6)/10**6
P1 = I**2*R1*1000
P2 = I**2*R2std*1000

#Result
print("R1 = %.1f k-ohm\nR2 = %.2f k-ohm = %.1f k-ohm(standard value)\nRsc = %.1f ohm"%(R1/1000,R2/1000,R2std/1000,Rsc))
print("\nPower wattage:\nPsc = %.0f mW\nP1 = %.3f mW\nP2 = %.3f mW"%(Psc,math.floor(P1*1000)/1000,P2))
print("Hence, both R1 and R2 may be selected safely of 1/16th watt power rating.")

R1 = 4.7 k-ohm
R2 = 6.58 k-ohm = 6.8 k-ohm(standard value)
Rsc = 1.0 ohm

Power wattage:
Psc = 360 mW
P1 = 5.112 mW
P2 = 7.397 mW
Hence, both R1 and R2 may be selected safely of 1/16th watt power rating.

example 11.4, Page No. 426

In [7]:
# Regulator design using IC 723(refer to fig. 11.26)

import math
#Variable declaration
Vout = 6                    # output voltage
Il = 1                      # load current
Isc = 0.250                 # short circuit 
Vref = 7                    # reference voltage
Vbe = 0.7                   # base-emitter junction voltage

#Calculations
R1 = 2.7*10**3              # assumed
R2 = Vout*R1/(Vref-Vout)
kRsc = Vbe/Isc
k =1-(((Il-Isc)*kRsc)/Vout)
R4 = 10*10**3                # assumed         
R3 = (1-k)*R4
Rsc = kRsc/k
R = (R1*R2)/(R1+R2)

#Result
print("R1 = %.1f k-ohm\nR2 = %.1f k-ohm\nR3 = %.1f k-ohm\nR4 = %.1f k-ohm\nR  = %.2f k-ohm"%(R1/1000,R2/1000,R3/1000,R4/1000,R/1000))

R1 = 2.7 k-ohm
R2 = 16.2 k-ohm
R3 = 3.5 k-ohm
R4 = 10.0 k-ohm
R  = 2.31 k-ohm

example 11.5, Page No.432

In [16]:
# Current source design using IC7812

import math
#Variable declaration
RL = 25.0           # load resistance
P = 10.0            # power 
I = 0.5             # current required
V = 12.0            # rated voltage

#Calculations
R = V/I
Vout = V+(I*RL)
Vin = Vout+2

#Result
print("R    = %d ohm\nVout = %.1f V\nVin  = %.1f V"%(R,Vout,Vin))

R    = 24 ohm
Vout = 24.5 V
Vin  = 26.5 V

example 11.6, Page NO. 432

In [20]:
# min and max voltage of regulator(refer fig.11.34)

import math
#variable declaration
Iq = 10*10**-3             # quiescent current
Vreg = 15.0                # regulated output voltage
R2 = 0                     # min value of potentiometer
R1 = 40.0                  # R1 resistor

#Calculations
Vout = (1+(R2/R1))*Vreg+(Iq*R2)

#Result
print("Vout = %d V"%Vout)

Vout = 15 V

example 11.7, Page No. 432

In [23]:
# current source using 7805

import math
#Variable declaration
Il = 0.2              # required load current
RL = 22.0             # load resistance
P = 10.0              # required power
Iq = 4.2*10**-3       # quiescent current
Vr = 5                # regulated output voltage

#Calculation
R = Vr/(Il-Iq)
Vout = Vr+Il*RL
Vin = Vout+2

#Result
print("R = %f ohm\nVout = %.1f V\nVin = %.1f V"%(R,Vout,Vin))
# Answer for R is wrong in the book

R = 25.536261 ohm
Vout = 9.4 V
Vin = 11.4 V

example 11.8, Page No.435

In [6]:
# Regulated outpuut voltage(refer fig. 11.38)

import math
#Variable declaration
R1 = 220.0                 # resistance R1
R2 = 1500.0                # Resistance R2
Iadj = 100*10**-6          # adj. current


#Calculartions
Vout = (1.25*(1+(R2/R1)))+(Iadj*R2)

#Result
print("Vout = %.2f V"%Vout)

Vout = 9.92 V

example 11.9, Page No. 435

In [8]:
# Output voltage range

import math
#Variable declaration
R1 = 820.0              # resistance R1
R2min = 0               # min potentiometer resistance
R2max = 10*10**3        # max potentiometer resistance
Iadj = 100*10**-6       # adj. current

#calculations
Vmin = 1.25*(1+(R2min/R1))+(Iadj*R2min)
Vmax = 1.25*(1+(R2max/R1))+(Iadj*R2max)

#Result
print("The output can be varied in the range %.2f V to %.2f V"%(Vmin,Vmax))

The output can be varied in the range 1.25 V to 17.49 V

example 11.10, Page No. 436

In [12]:
# Maximum load current

import math
#Variable declaration
Vbe = 1.0                # base emitter junction voltage
beta = 15.0              # current gain
R1 = 7.0                 # resistance R1
Iout = 1.0               # max output current from IC  
#Calculations
Il = ((1+beta)*Iout) - beta*(Vbe/R1)
Il = math.floor(Il*100)/100
#Result
print("IC which can supply maximum 1A can supply maximum load of %.2f A, with the help of the current boosting arrangements"%Il)

IC which can supply maximum 1A can supply maximum load of 13.85 A, with the help of the current boosting arrangements