Electronic Circuits & Systems - Linear Voltage Regulators (Calculations and LTSPICE simulations) - 02/05/2018 01:39 EDT


Description Below is copy and pasted from there

Approach this as if you are teaching it to a class


Below is the schematic of a voltage regulator.

Let Vi = 8V, Vref = 2.5V, Rf = 10kΩ, RL = 50Ω, CL = 10nF and a(s) = 1031 + s2.5*106

with the output resistance of the opamp being 200kΩ, and neglecting the input capacitances. The output transistor has λ = 0.005V-1, and (VGS - VT) = -500mV when delivering the required load current to the load resistance of 50Ω. Compensate this regulator so that it is stable with 45° phase margin, if only the resistive part of the load varies in the range

10 ≤ RL ≤ 10kΩ. What is the load regulation over this range of loads?


The voltage regulator LM723 can supply up to as high as 150mA without an external pass transistor. The reference voltage inside the regulator is a Zener reference of about 7.2V. You are to design a regulated power supply of 5V sourcing a maximum of 100mA. The load is a variable resistor with a minimum 50Ω. You need to use a load resistor with a proper power rating because it will be very hot at the maximum current. Use the nominal supply voltage of 12V. Also add a short circuit protection feature so that your maximum output short current can be limited to a little over 100mA.

Handwritten/Calculation part:

Your hand sketch of the design.

Brief reasoning on how you designed your regulator.

Discuss how you are going to make your regulator stable.

Estimate the load regulation.

Everything below MUST be simulated in LTspice

Build your regulator, and check stability first. For stability check, apply a step voltage source in series with the load. Get a step response, and observe whether it rings severely or not.

Once made stable, check the minimum input voltage to make this regulator work. Measure the line regulation by varying the input from 10V to 15V. Explain what may have caused this change in the output current.

Note for both 6 and 7 when simulating in SPICE, you should use the .sweep command in combination with the .op simulation command to vary the input voltage and load resistance respectively

Measure the load regulation for the output current from 0 to 100mA by varying the load resistance value. Compare it with your hand calculation. Since the output voltage doesn't change much, you need to measure both current and voltage with very high precision for 6 and 7.

Add a current meter between the output and the ground, and measure the short circuit current.

Need Done in 24 hours

Skills: Circuit Design, Electrical Engineering, Electronics, Engineering, Matlab and Mathematica

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