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    EXPT. No. 7 VOLTAGE TO FREQUENCY CONVERTER

    Uploaded by

    Hritik Kumar
    1. The document describes a voltage to frequency converter circuit that uses op-amps, transistors, diodes, and resistors. 2. The circuit works by charging a capacitor at a rate determined by the input voltage Vi. When the capacitor voltage drops below -5V, the transistor turns on and the capacitor discharges quickly. This creates a square wave output whose frequency depends on the input voltage Vi. 3. Replacing the zener diode with a resistor causes the circuit to stop working because without the zener diode, the first op-amp's second pin is no longer grounded, preventing the circuit from functioning properly.

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    EXPT. No. 7 VOLTAGE TO FREQUENCY CONVERTER

    Uploaded by

    Hritik Kumar
    393 views2 pages
    1. The document describes a voltage to frequency converter circuit that uses op-amps, transistors, diodes, and resistors. 2. The circuit works by charging a capacitor at a rate determined by the input voltage Vi. When the capacitor voltage drops below -5V, the transistor turns on and the capacitor discharges quickly. This creates a square wave output whose frequency depends on the input voltage Vi. 3. Replacing the zener diode with a resistor causes the circuit to stop working because without the zener diode, the first op-amp's second pin is no longer grounded, preventing the circuit from functioning properly.

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    1. The document describes a voltage to frequency converter circuit that uses op-amps, transistors, diodes, and resistors. 2. The circuit works by charging a capacitor at a rate determined by the input voltage Vi. When the capacitor voltage drops below -5V, the transistor turns on and the capacitor discharges quickly. This creates a square wave output whose frequency depends on the input voltage Vi. 3. Replacing the zener diode with a resistor causes the circuit to stop working because without the zener diode, the first op-amp's second pin is no longer grounded, preventing the circuit from functioning properly.

    Copyright:

    © All Rights Reserved
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
    393 views2 pages

    EXPT. No. 7 VOLTAGE TO FREQUENCY CONVERTER

    Uploaded by

    Hritik Kumar
    1. The document describes a voltage to frequency converter circuit that uses op-amps, transistors, diodes, and resistors. 2. The circuit works by charging a capacitor at a rate determined by the input voltage Vi. When the capacitor voltage drops below -5V, the transistor turns on and the capacitor discharges quickly. This creates a square wave output whose frequency depends on the input voltage Vi. 3. Replacing the zener diode with a resistor causes the circuit to stop working because without the zener diode, the first op-amp's second pin is no longer grounded, preventing the circuit from functioning properly.

    Copyright:

    © All Rights Reserved
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
    of 2

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    Indian Institute of Technology Patna


    Department of Electrical Engineering
    IIT Patna, Campus, Bihta, Patna, Bihar – 801103 Experiment- 7

    VOLTAGE TO FREQUENCY CONVERTER


    OBJECTIVE: Designing a voltage to frequency converter.
    COMPONENTS REQUIRED

    :
    Op-Amp : Two LM741.
    Transistor : One 2N2222A
    Diode : one 6.2V zener diode.
    Resistance : One 330, One 1kΩ, two
    2.2KΩ, one 3.9KΩ, one 5.6KΩ,
    two 10 kΩ, three 100 kΩ.
    : Capacitor : One 10 µF.

    PRECAUTIONS AND GUIDELINES Fig 7.1

    1. The op-amp (Fig 7.1) generally works on split power supply (e.g. ±12 V). Both positive and negative
    power supplies must be present whenever op-amp is powered. The range of power supply is from ±5 V
    to ±15 V. Do not forget to connect the common terminal of the power supply to the ground on the
    breadboard.

    2. Connecting only one side of power supply or interchanging positive and negative power supplies
    damages the op-amp.

    3. While switching on the set-up, switch on the oscilloscope first, then the power supply to the circuit,
    and finally the function generator. When switching off, follow the sequence in reverse order.
    4. For any IC, never exceed the input voltage beyond the power supply limits.

    5. Keep ground terminals of the oscilloscope probes and function generator output, and power supply
    common connected together throughout the experiment.

    The circuit shown in Fig. 7.2 is of Voltage to Frequency converter

    Working Principle: Initially, the capacitor C gets charged at constant rate of (Vi / R3) amp. The output
    voltage Va at point ‘a’ drops linearly till this voltage is not less than the voltage Vb at point ‘b’ which is
    approx. at about -5.0V. Note that, the comparator output voltage VC is at approx. -12V when Va is greater
    than -5.0V and the transistor is in ‘off’ state.

    When the negatively increasing voltage Va becomes less than -5.0V, the comparator output Vc goes to
    approx. +12V. The transistor gets ‘on’ and hence the emitter voltage (also voltage at comparator ‘+’ input)
    of the transistor is about at zero voltage. The transistor is in saturated state. The capacitor starts
    discharging. The discharging continues and Va increases positively, till Va becomes greater than zero
    voltage. The comparator output VC becomes about -12V and the transistor becomes ‘off’. This charging
    and discharging process repeats again and again. Note that the discharging duration is same for any input
    voltage Vi and it should be much smaller than the charging time, which depends on the input voltage Vi.
    Pre-experiment Reading:

    (a) Draw the waveforms at (i) Va (ii) Vb and (iii) Vc


    (b) Compute the charging time of the capacitor.
    (c) Compute the discharging time of the capacitor.
    (Assume Vi= 4V for above)

    Fig 7.2 Voltage to Frequency Converter

    OBSERVATIONS:
    1. Connect the circuit as shown in Fig 7.2 with R1 = 1 kΩ, and R2 = 1 kΩ. Make sure the power supply ground is
    connected to the circuit ground.
    2. Observe the waveform Va at point ‘a’ for
    (a) for R2 = 1 KΩ
    (b) for R2 = 2.2 KΩ
    (c) for R2 = 3.9 KΩ
    (d) for R2 = 5.6 KΩ
    and measure frequency form the output at point (Vc)
    3. Similarly, observe the waveform Vb at point ‘b’ for all Vi as in step 2.

    4. Remove the zener diode and replace it by a resistance so that Vb is approx. at -5.0V and observe Vb (both
    frequency and pulse width). The circuit doesn't work now. Explain why the circuit has stopped working.
    {Observe voltage of pin-2 of first op-amp (LM741) and note that it is no longer at 0 volt (grounded). [Explain why
    pin-2 is no longer grounded]}.
    ----------------------------

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