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LM741: Circuit Design of Capacitance Measurement

  • Contents

Introduction

The LM741 series are general-purpose operational amplifiers. It is intended for a wide range of analogue applications. The high gain and wide range of operating voltage provide superior performance in integrator, summing amplifier, and general feedback applications. This article will introduce the circuit of capacitance measurement composed of LM741.

Catalog

Introduction

Catalog

I Circuit Design

FAQ

Ordering & Quantity

I Circuit Design

As Figure 1 shows, the measuring principle of this circuit is: a triangular wave is formed from the process of charging and discharging of measured capacitor Cx. And the capacitance can be measured by the oscillation period of the triangular wave. A Miller integrating circuit consists of A1. A Schmidt circuit consists of A2 and the Schmidt circuit forms positive feedback and generates oscillation. Its amplitude is determined by R4 and R3, equal to 1 / 3 of the supply voltage. The charging current of Cx is determined by the supply voltage and R2, and the discharge current is determined by the supply voltage and R1 + R2. In principle, the oscillation period should not be affected by the supply voltage. However, due to the limitation of A2 differential input voltage and the constant of transistor driving circuit, it is not allowed to change the supply voltage greatly. The range of power supply voltage  is ±13 to ±15V. The absolute values of positive and negative supply voltages need to be equal.
When the capacitor Cx is not connected, A2 oscillates with a delay of about 20 μS, and Cx can be calculated to compensate for this. The measurement time is 10S when the Cx capacitance is 1000μF. If R1 and R2 use 1KΩ resistance, the measurement time can be shortened to 1/10.

Circuit output U. The capacitance can be read out by connecting a external counter.

Figure 1. capacitance measurement circuit

LM709 forms a positive feedback through R7 and VT2 to the negative input to form a Schmidt trigger. 

When LM709 outputs a high level, VT2 is saturated and turned on, and the voltage of C pole of VT2 is 0V. Both VT3 and VT1 are cut off. The +15V power supply charges Cx through R1 and R2, and the output voltage of the LM741 gradually decreases. When it drops to 0V, Schmidt reverses and the output voltage goes low (-15V). At this time, VT2 is cut off, and the voltage of C pole of VT2 rises to +5V, consolidating the low-level output state of LM709. At the same time, VT3 and VT1 get the base current and turn on. The CX is reversely charged via R2 and -15V power supplies. The output voltage of LM741 increases gradually. When it rises to + 5V, Schmidt reverses again and the output becomes high level. Then a cycle complete. The above process is repeated to form periodic oscillations.


FAQ

  • What is lm741 op amp?

An LM741 operational amplifier is a DC-coupled high gain electronic voltage amplifier. It has only one op-amp inside. An operational amplifier IC is used as a comparator which compares the two signal, the inverting and non-inverting signal.

  • Why Opamp is called 741?

The 741 Op Amp IC is a monolithic integrated circuit, comprising of a general purpose Operational Amplifier. It was first manufactured by Fairchild semiconductors in the year 1963. The number 741 indicates that this operational amplifier IC has 7 functional pins, 4 pins capable of taking input and 1 output pin.

  • How does a 741 op amp work?

The most common Op-Amp is the 741 and it is used in many circuits. The OP AMP is a 'Linear Amplifier' with an amazing variety of uses. Its main purpose is to amplify (increase) a weak signal - a little like a Darlington Pair. The OP-AMP has two inputs, INVERTING ( - ) and NON-INVERTING (+), and one output at pin 6.

  • How do you calculate lm386 gain?

Voltage Gain Analysis:
Without any external components, it has a gain of Gv = 2x15K/(150+1350) = 20 (26 dB).
With a capacitor (or shortcutting) between pins 1 and 8 , it has a gain of Gv = 2x15K/150 =200 (46dB).

  • Why does the IC 741 require dual power supply?

Operational amplifiers have two power supply rails because they usually need to swing bipolar - output voltages that go either positive or negative in response to the normal range of input signals. ... Without the dual supplies the output signal would clip at the ground potential.

  • How do I check my 741 IC?

Testing a 741 IC
The circuit is commonly called as voltage follower. A voltage is applied to pin3 of the op-amp through the variable resistor (10K). All we need to do is to verify whether the voltages V1 and V2 are exactly same or not. Check them using a multi-meter.

  • What is IC 741?

An op amp is a complex electronic device, which consists of resistors, capacitors, transistors and diodes. It is commercially available in integrated circuit form. Most commonly available and used op amp IC is IC 741. The IC 741 is a small chip. It comprises eight pins.

  • What is gain bandwidth product of 741?

Gain-Bandwidth Product: For an Op-Amp the gain, G is defined as the gain when a signal is fed differentially into the op-amp and no feedback loop is present. ... It is generally given in V/μs, and for the 741 op-amp is something close to 1v/μs.

  • What are the features of IC 741?

Short circuit and overload protection provided.
In theory, the dc output voltage will be zero if both the inputs of the 741 IC are connected to the ground. …
Low power consumption.
Large common mode rejection ratio (CMRR) and differential voltage ranges.
No external frequency compensation is required.

  • Which op-amp (LM356 or LM741) is the better choice for higher frequency applications?

Um, the LM356 is an audio power amplifier with a 300 KHz bandwidth. The LM741 is an operational amplifier with a typical unity gain bandwidth of 1 MHz.
In other words, they are entirely different sorts of things and not at all interchangeable.
Neither is very good at higher frequencies.
You might be thinking of the LF356, which is a JFET input operational amplifier with a unity gain bandwidth around 5 MHz. Much better part in almost every dimension than the LM741.

  • Can we use an LM324 instead of an LM741 for constructing an op-amp integrator?

Yes. It will likely perform slightly better too as it has a slightly better specification (frequency, slew rate, etc), plus you get four identical op amps in a single 14 pin package.

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