Question

Design low voltage regulator using 723 with 5v output.​

Answer 1

Answer:

Step 1 : Selection of R1 and R2

Let VR2 = Regulated DC output = 5V

Current I through R1 & R2 be 1mA

R2=VR21mA=51mA

R2=5KΩ

VR1=VREF−VR2

VR1=7.15−5

VR1=2.15V

R1=VR11mA=2.151mA

R1=2.15KΩ

Step 2 : Selection of R3

R3=R1||R2

R3=2.1K||5K

R3=1.5KΩ

Step 3 : Selection of RSC

RSC=VSENSEISC

Assume VSENSE = 0.5V and ISC = 200mA

RSC=0.5200m

RSC=1.5KΩ

Step 4 : Selection of Q3

PDT3=VCE3×IC3

 

PDT3=(Vin−VO)×IC3

Assume Vin = 12V

PDT3=(12−5)×2

PDT3=14W

β=ILIB=2A150mA

Assume IB = 150mA

β=13.33

under short circuit condition, VO = 0V

PDT3=VCE3×ISC

PDT3=(Vin−VO)×ISC

 

PDT3=(12−0)×200mA

PDT3=2.4W

Select transistor whose PDT3 ≥ 2.4W and β ≥ 13.33

Step 5 : Selection of RL

RL=VOIL

RL=52

RL=2.5Ω