Jawaharlal Nehru Technological University Hyderabad B.Tech III LINEAR AND DIGITAL IC APPLICATIONS Previous Question Paper (September 2021 - R16)

An ideal integrator is an operational amplifier circuit where the feedback element is a capacitor. The output voltage V_o is proportional to the time integral of the input voltage V_i. The relationship is given by:

When a square wave is applied as the input:

• During the positive half-cycle of the square wave, the input voltage is constant at +V. The integration of a constant value results in a negative-going ramp output.
• During the negative half-cycle of the square wave, the input voltage is constant at -V. The integration of a negative constant results in a positive-going ramp output.
• As the input square wave alternates between positive and negative levels, the output waveform becomes a triangular wave.

The slope of the output ramp is determined by the RC time constant. If the frequency of the square wave is high relative to the integrator's time constant, the output amplitude decreases. In an ideal integrator, the output continues to ramp linearly as long as the input remains constant, assuming the op-amp has infinite gain and bandwidth.

The IC 78XX series is a family of fixed positive voltage regulators commonly used in electronic circuits to provide a stable output voltage from a higher, fluctuating input voltage. The 'XX' in the part number represents the fixed output voltage (e.g., 7805 provides +5V, 7812 provides +12V).

Pin Configuration: The IC 78XX is typically available in a TO-220 package with three pins:

• Pin 1 (Input): The unregulated DC voltage is applied here. It must be at least 2V to 3V higher than the rated output voltage to ensure proper regulation.
• Pin 2 (Ground): This pin is connected to the common ground of the circuit.
• Pin 3 (Output): This pin provides the regulated, stable output voltage.

Key Features:

• Internal Protection: These regulators include internal thermal overload protection and short-circuit current limiting, which automatically shuts down the device if it overheats or experiences an output short.
• Efficiency: Being linear regulators, they dissipate excess power as heat, often requiring an external heat sink for higher current applications.
• Capacitor Requirements: It is standard practice to place a 0.33μF capacitor at the input and a 0.1μF capacitor at the output to improve transient response and stability.