358 Op Amp
The 358 op amp (LM358) is a dual operational amplifier that features low cost and low power. It contains two op amps and is available in a variety of useful packages.
The LM358 is one of the most popular integrated circuits and op amps of all time.
Overview of the 358 Op Amp
An operational amplifier (or op-amp) is a high-gain direct-coupled amplifier. In the term operational amplifier, “operational” means that the amplifier can perform certain operations such as summation, subtraction, comparison, etc. The word “amplification” means that it can amplify the input signal.
An operational amplifier is an electronic amplifier that amplifies an electrical potential difference present at its inputs. It was initially designed to perform mathematical operations in analog computers: it allowed to model basic mathematical operations such as addition, subtraction, integration, derivation and others.
Later, the operational amplifier was used in many other applications such as motor control, voltage regulation, current sources or oscillators.
Physically, an operational amplifier is made up of transistors, electron tubes or any other amplifying components. It is commonly found in the form of an integrated circuit.
The LM358 is an excellent, low-power, easy-to-use two-channel operational amplifier. This IC is designed for general uses such as amplifiers, high and low pass filters, very low frequency band pass filters and analog adders, and being internally compensated it can be configured as a 1 gain buffer. The LM358 family of components was born to cost little even at the expense of performance.
The 358 op amp consists of two independent high-gain operational amplifiers with internal frequency compensation. It is specifically designed to operate from a single power supply over a wide voltage.
The LM358 is a good standard operational amplifier. It can handle a 3 to 32 V DC power supply and source up to 20 mA per channel. This op-amp is suitable, if you want to use two separate op-amps with one power supply.
History of the LM358 Op Amp
We owe the term operational amplifier to John R. Ragazzini in 1947. Operational amplifiers were initially developed in the era of electronic vacuum tubes which was for a long time the only existing active component. It allowed the manufacture, often in large series, of the first electronic devices: radio, television, radar receivers, etc.
Over time, these devices as well as computers, required more and more active functions, making the problems of volume, consumption and reliability of the electronic tube prohibitive, despite numerous improvements.
In 1972, National Semiconductor first introduced an amplifier technique suitable for operation in a low-voltage, single-powered environment. This amplifier, which would become the LM324, became the industry’s low-cost standard quad op-amp.
It was then followed by a similar operational amplifier, the LM358, which is a low-cost standard dual op-amp. The LM358 is now an industry-standard integrated circuit manufactured by multiple industry-leading companies including: National Semiconductor, Texas Instruments, STMicroelectronics and more…
358 Op Amp Pin-Out
The abbreviation LM358 indicates an 8-pin integrated circuit, containing two low-power op-amps. The pin configuration of the LM358 IC is as follows:
• Pin 1: Output (Vout) pin of the first operational amplifier.
• Pin 2: Inverting input pin of the first operational amplifier.
• Pin 3: Non-inverting input pin of the first operational amplifier.
• Pin 4: Ground/negative pin for both operational amplifiers.
• Pin 5: Non-inverting input pin of the second operational amplifier.
• Pin 6: Inverting input pin of the second operational amplifier.
• Pin 7: Output (Vout) pin of the second operational amplifier.
• Pin 8: Power supply (V+) pin for both operational amplifiers.
358 Op Amp Packages
358 Op Amp DSBGA
DSBGA or Die-Size Ball Grid Array, has become increasingly popular for surface mount ICs that require high density connections. Using the under-side of the integrated circuit package rather than connections around the edge like in DIP packages, this enables connection density to be reduced and simplifying PCB (Printed Circuit Board) layout. For this package, the LM358 operational amplifier typically comes in a size of 1.31 mm wide and 1.31 mm large.
358 Op Amp SOIC
SOIC is an abbreviation for Small Outline Integrated Circuit, which is a surface mount
(SMT) IC package that occupies approximately 30-50% less area than an equivalent in-line dual package (DIP), with a typical thickness of 70% less.
358 Op Amp PDIP
PDIP, or Plastic Dual In-line Package is one of the oldest plastic IC packages still in use today.
It is rectangular in shape and has wires running on both sides along its length, forming two sets of in-line pins. The LM358 that comes in this package usually has a size of 9.81 mm wide and 6.35 mm large.
How the 358 Op Amp Works
Operational amplifiers typically consist of at least three stages: a differential stage, one or more voltage boosting stages and a voltage buffer.
The differential input stage usually consists of a differential pair. It provides the differential amplification between the two inputs as well as the high input impedance. The differential stage can include a bias current compensation system. In this case, the base of each input transistor is connected to the collector of a transistor which then provides the current necessary to bias the differential input pair.
The amplification stage is generally a high gain, class A amplifier. The capacitance present in the voltage amplification stage allows for frequency compensation.
The voltage buffer, which serves as an output stage, has a voltage gain of one, it allows the operational amplifier to provide high output currents with a low output impedance. It also includes current limitations and short circuit protection.
For the 358 operational amplifier, it can operate in three different modes depending on the way it’s wired:
• The op-amp operates in open loop if there is no electrical path between the output and any of the inputs (except the path through the ground M).
• The op-amp operates in closed loop on the + if there is a path between the output and the input Vin+ (not counting the path that passes through the ground M).
• The op-amp operates in a closed loop on the – if there is a path between the output and the input Vin- (not counting the path that passes through the ground M).
The concept of perfect or ideal operational amplifier allows us to reason about the theoretical functioning of the operational amplifier, freeing us from the parasitic phenomena and limitations inherent in the technological reality of the components.
The progress made since the first op-amps tends, through the constant improvement of performance, to get closer to the model of the ideal op-amp.
A perfect operational amplifier has its input impedance, differential mode gain, slew rate and bandwidth infinite while its common mode gain and output resistance are zero. Moreover, it has no offset voltage and no bias current.
In reality, the differential gain of an operational amplifier varies greatly with frequency, so it is common to consider it as infinite in order to simplify calculations. It is also possible to consider the gain of an operational amplifier as being that of a pure integrator in order to get closer to the real behavior of the amplifier.
These characteristics reflect the fact that a perfect operational amplifier does not disturb the signal it amplifies and that its output voltage depends only on the voltage difference between its two inputs.
Although the perfect operational amplifier model allows us to calculate the transfer function and understand most op-amps-based circuits, real op-amps have a number of limitations compared to this model.
A real operational amplifier has the following defects: presence of an offset at the input, influence of the common mode voltage on the output voltage, non-zero impedance at the output, non-infinite impedance at the input, and variation of the gain with frequency.
Moreover, the output voltage can be influenced by supply voltage variations and has a finite slew rate.
To sum up, here are the key points regarding the characteristics of the 358 operational amplifier:
• Two internal frequency-compensated operational amplifiers
• Voltage gain: 100 dB
• Offset voltage: 2 mV
• Wide bandwidth: 1 MHz
• Single and dual power supplies
• Single power supply range: 3V to 32V
• Dual power supply range: + or – 1.5V to + or – 16V
• Low supply current drain: 500 μA
• Common Mode Rejection Ration (CMRR): varies between 65 dB and 85 dB.
Gain: the rate of voltage amplification; the number of times the input voltage will be multiplied.
Offset voltage: Normally in theory, the output voltage of an operational amplifier is proportional to the voltage difference between its inverting and non-inverting inputs.
If we apply an identical voltage on both inputs, the output voltage should be zero. However, this is often not the case, we can see the presence of a DC voltage of a few mV which is due to the imperfections of the differential input stage.
In fact, this offset voltage corresponds to the difference in voltage that should be applied between the inverting and non-inverting inputs to have 0V at the output.
Some operational amplifiers have one or more inputs to cancel this offset voltage, others do not. This offset voltage is sometimes disturbing especially when a high gain is assumed as the offset voltage is multiplied by the gain. But sometimes depending on the application, this offset voltage does not cause troubles.
Bandwidth: the frequency range in which the operational amplifier can operate with acceptable gain. It is often expressed for a gain of 1. The higher the gain required of an op-amp, the smaller its bandwidth.
Power supply: many operational amplifiers are designed to be powered preferably with a dual power supply (one positive connected to the +V pin, and one negative connected to the -V pin). Some models of op-amps are nevertheless satisfied with a single power supply (the most positive terminal of the power supply connected to the +V pin, and the most “negative” terminal connected to the ground). An AOP designed to work with a dual power supply can
however be used with a single power supply. The 358 op-amp can be powered using either of
these power supplies.
Supply current drain: The power consumption is generally in the order of mA for an operational amplifier. Some consume very little current (a few tens of uA, like in this case of the 358 op-amp) while others require several mA. Generally speaking, the op-amps capable of high frequency require a higher current intensity.
Common Mode Rejection Ration: The CMRR is a numerical value that represents the ability of an operational amplifier to reject the common voltage of its two inputs. It is usually expressed in decibels (dB). In practice, the output voltage of an op-amp does not only depend on the voltage difference between these two inputs, but also depends on the average value of the voltages on these two inputs (or common mode voltage).
358 Op Amp Applications
Voltage Follower with LM358
The voltage follower circuit is, without a doubt, the most basic feedback circuit available!
This is because there are no additional components. Instead, the operational amplifier is simply “looped on itself” at its -Vin input.
Since it is called a “voltage follower”, it is a circuit which allows to generate an output voltage equal to the one presented at the input, and there is no link between the input +Vin and the output Vout.
One would say, but what is the use of such a circuit, if it outputs the same voltage as the input? Because there would be no need for an operational amplifier to do that!
But here, the op-amp brings something quite remarkable. Indeed, the op-amp mounted as a voltage follower allows to draw no current on the input (or very little), while being able to deliver “a lot” of current on the output. This makes this circuit very popular with those who wish to interface a sensor sensitive to load current, for example, in order to exploit the signal supplied without disturbing it. Another example is the interfacing at the output of a microcontroller. Indeed, if the latter cannot provide enough output current, then a solution is to connect an operational amplifier mounted as a voltage follower, so that it can deliver more output current.
Integrating Circuit with 358 Operational Amplifier
An operational amplifier can perform several mathematical operations. Let’s look at how an operational amplifier can perform an “integration” operation on an input signal. To implement the integrator using the 358 op-amp, we need a capacitor and some resistors, and the LM358 op-amp! The circuit diagram below represents the op-amp integrator circuit.
In this circuit, Vin is the input voltage supplied into the inverting terminal, and the noninverting terminal is grounded. The same current will flow through the feedback path, having a capacitor in it.
The output voltage is proportional to the time integral of the input voltage and that is why the circuit is called integrator.
An electronic oscillator is a circuit whose function is to produce a periodic electrical signal, sinusoidal, square, sawtooth, or any other shape. An oscillator circuit can have a fixed or variable frequency.
With this circuit, the op-amp delivers a repetitive (or periodic) signal of square shape. Note that sometimes it does this when it is not asked to do so (parasitic oscillation), and this is obviously very annoying in this case.
By adding another resistor and a capacitor, it is possible to realize a Wien bridge oscillator delivering a sinusoidal voltage.
358 Op Amp Circuits and Projects
Shock Alarm Using the 358 Op Amp
The following circuit is a shock alarm circuit that is used in a wide variety of fields, from houses to automotive industry. The main application of this circuit is in the automotive industry as an anti-theft alarm. In this circuit, a piezoelectric sensor is used, which should be attached to the door you need to protect. Here, the LM358 is connected as an inverter Schmitt trigger, and resistor R3 is used as feedback resistor.
When the piezo sensor is not activated, then the output signal of the sensor will be low. When the piezoelectric sensor is triggered, then the output signal of the sensor will go high and activate the Schmitt Trigger which then triggers the buzzer. The buzzer sound is reminiscent of the beep sound sometimes even if the vibration is detached. Because when the inverting input goes high it has a small effect on the LM358 IC when it is activated.
This LM358 IC based darkness detector is used to detect the presence or absence of light using a light dependent resistor (LDR), photodiode or a phototransistor. In this project we are using an LDR and an LM358 operational amplifier. The components required to make this project are LDR, LM358 IC, 9V power supply, resistors: 330R, 1K, 10K, variable resistor of 10K and a transistor.
In the following sensor circuit, if you stop the light from reaching the light dependent resistor, then the LM358 immediately turns the LED on. Depending on the light intensity in your room, you must adjust the variable resistor to calibrate the sensitivity of the circuit.
Alternatives to the 358 Op Amp
The 301 operational amplifier was designed by Bob Widlar in 1967 and still produced 50 years after launch. It performed well against other operational amplifiers in its range, but the need for one or more external compensation capacitors reduced its spreading.
The 324 operational amplifier consists of four independent high gain frequency compensated operational amplifiers. It is specifically designed to operate from a single or dual power supply over a wide voltage range. Its pinout has become a standard for op-amps, and it continues to be one of the best-selling op-amps in the world.