Let’s look at the amplifier circuit of one of the popular LM324 IC, its pinout and suitable equivalents for replacement in case of failure. It is made as four identical operational amplifiers (Op-Amps), assembled in a single case, working from a single power supply in a wide voltage range. Each op-amp has an input differential stage, short-circuit protection and an internal frequency correction for single gain.
The specifications and low cost of this device ensure that it is widely used in amateur radio circuits and industrial electronics. It is excellent for use in compact portable electronic devices.
IC is produced in DIP-type packages: plastic CDIP, ceramic PDIP or SO-type for surface mounting:
- – SOIC;
- – TSSOP.
The LM324 pinout for the different packages is identical:
- 2,3,5,6,9,10,13,12 – inputs;
- inputs, 1,7,8,14 – output;
- 4 – positive supply (Vcc);
In the picture above you can look at the pin configuration lm324n.
Technical specifications lm324
- Supply voltage range Up. (Vcc): unipolar source: +3…30 V, bipolar source: ±1.5…±15 V (V);
- Differential input voltage Udif.(VIDR): 32 V (V);
- Input Voltage. Uin (VICR): -0.3…32 V (V); IICR input current (VICR): ±1.5;
- IICR input current (when VICR is negative) 5 mA (mA);
- IICR input current (with positive VICR) 0.4 mA (mA).
Electrical parameters (at Up +5 V and TA +25 °C):
- Input bias voltage Ucm (VIO) of 2…7 mV (mV);
- Input bias current Iin(IIB) from 45…100 nA;
- Output Voltage. U output(Vout): 0…Up. – 1.5 V (V);
- Gain (K): 100 dB (dB);
- Bandwidth (f): 1 MHz;
- No-load current consumption Ip. (ICC): not more than 700 μA (µA); chachip
- Input current difference (bias current) Icdc (IIO): 5…30 nA (nA);
- Power dissipation RR max (P tod) depends on the case type: PDIP 1130 mV(mW); CDIP 1260 mV(mW); SOIC 800 mV(mW).
- Ambient operating temperature range TA: 0…+70°C;
- Storage temperature Tst. (Tstr):-65…+150 °C.
Specs lm324 different companies slightly differ from each other, so when you develop your circuit, it is recommended to read the official technical documentation for the used device from a particular manufacturer.
The differential range of the input voltage reaches the supply voltage. For the lm324, the lower limit of the input in-phase range is 0.3 V lower than V-, and the output voltage swing is limited below the V- value. Both inputs and outputs are limited to 1.5 V less than V+.
The unit amplification frequency fi (100 kHz to 30 MHz) is the frequency at which the gain of the chip becomes unity (0dB).
It has an internal frequency correction for the single gain.
The input common-mode voltage range includes ground.
Short-circuit duration Tkz (Tsc) at the output is unlimited.
The operation of the lm324n IC is based on the simultaneous operation of four Op-Amps inside it. All amplifiers are powered from a single power supply, have inverting, non-inverting inputs and a single output. The power supply can be unipolar or bipolar.
Let’s look at the internal circuit of one of the operational amplifiers with unipolar power supply. We will take it directly from the LM324 datasheet.
Functionally each operational amplifier consists of a differential stage, as well as intermediate and output amplification stages.
The differential stage performs the functions of amplifying the difference of input voltages (V+ and V-) and neutralizing in-phase signals. It provides high input impedance.
The intermediate stage provides balancing of the operator (setting zero voltage at the output when inputs are closed), coordination of resistances of differential and output stages, as well as frequency correction (protection from self-excitation).
Output stage provides low output resistance, required power in the load, current limitation and short-circuit protection.
The LM series is based on integrated circuits manufactured by National Semiconductor. The prefix LM originally stood for linear monolithic and was used to designate general-purpose amplifiers for which no stringent requirements were imposed. The digits “324” indicate the serial number of the chip. The “-N” at the end of the serial number refers to devices purchased by Texas Instruments from National Semiconductor. In September 2011, National Semiconductor was transferred to Texas Instruments, which did not change the LM prefix on its products. Therefore, currently the LM marking is the manufacturer’s code of Texas Instruments, but it is widely used by other manufacturers when producing their equivalents of this IC.
The LM324 ICs and the same one with the letter N have the same physical and electrical specifications. In many manufacturers the symbol “-N” at the end of the marking indicates the plastic housing type of the chip – DIP14.
It should also be noted that manufacturers are constantly improving their products. Currently, there are some superior modifications with a number of functions, such as: LM324K, LM324KA with internal protection against electric discharge (HBM ESD); micropower LP324 with current consumption of 21 microns; low voltage LMV324, with a supply voltage from 2.7 V to 5.5 V; LPV324, made by BiCMOS technology and current consumption of 9 microns, etc. Amplifiers with an “A” in the marking, such as the ” LM324A-N “, will have better VIO specs than others (without the “A”).
LM324 equivalents list:
There are also Russian equivalents:
Scope of application
The LM324 has found the greatest popularity with typical negative feedback circuits. It is used to create different multifunctional devices: integrators, differentiators, demodulators, logarithmic amplifiers, adders, add-subtractors, amplitude controllers, oscillators, etc. Due to the constant improvement of the device in question, there are many different devices using lm324, for example:
- motion sensor circuit diagram for lighting;
- Neptune incubator thermo regulator circuit, etc.
A simple LM324 amplifier circuit
Let’s take a look at one of the simplest negative feedback LM324 circuits, the voltage repeater. You usually start your op amp experiments with a voltage repeater. This circuit is also called an amplifier that has a voltage gain of unity. Ideally, this means that the op-amp does not provide any signal gain and the output voltage is the same as the input voltage. That is, if 5V is applied to the input of the operational amplifier, then 5V will be at its output.
But this statement is true for a perfect operational amplifier, not for the LM324 discussed in the article. Because it is not a virtual circuit, but a real one, its specifications differ from the ideal ones. Let’s look at the graph of output voltage vs. input voltage for the lm324.
In the graph, the area “A” shows the phase change at the output. This can happen when there is a negative voltage at the input of the IC and can lead to undesirable consequences – its failure.
Also, the graph shows that the voltage at the output of the amplifier increases as the input voltage increases. But it can not grow indefinitely, and is limited by the supply voltage of the IC and peculiarities of its work. So, the voltages at the inputs are slightly different, a small current flows through them, so the output voltage will be slightly different from the supplied voltage. In the graph, in the area “C”, you can see the output voltage limit of 3.8 V for the amplifier circuit in question, powered from 5 V.
In practice, it is common to work with active electronic components, which have a rather weak output current. For example, such as a microphone. Connecting a low impedance element to it will reduce the voltage of the output signal it produces. In such cases, you can use a voltage repeater, which has a large input and low output impedance, respectively will not reduce or distort the signal applied to the input.
A voltage repeater is not the most common typical application for this IC. Other typical solutions based on this Op-Amp are created and continue to be improved upon, which are the basis for modern electronic devices.
LED flashing light circuit on lm324
This circuit is very simple and allows to control switching on and off of light-emitting diodes smoothly. The blinker additionally uses two transistors. The capacity of capacitor C1 and base resistor R3 will determine the switching speed.
Safety in operation
Sometimes, not all lm324 channels are used in a project. If this is the case, the unused ones must be connected in such a way that they do not affect the others. Refer to the manufacturer’s datasheet for connection options for unused channels.
Under certain conditions the polarity of the output voltage can become inverted, which can damage the chip. This is typical in comparator and voltage repeater circuits. To avoid a negative voltage (phase inversion) at the input, manufacturers recommend adding a resistor in series to the non-inverting input of the circuit to limit the input current to 1 mA or less. This amount of input current will reduce the risk of damage to the device.
All operational amplifier inputs should not be connected directly to ground. Some resistance should always be added to limit the current to 10 mA or less. All input pins should include a diode from the input to Gnd. In circuits with two power supplies, the Gnd pin will be negative. However, during power on, power off, or sudden voltage faults, the Gnd pin can become positive. If this happens, a large current will flow across the grounded input pin that can damage the chip.
Adding a serial resistor from 1K ohm to 10K ohm at the input can save it from breakage.Do not connect to a power supply with reverse polarity, as lm324n can overheat and fail.
This chip is produced by many different companies to this day. DataSheet from each manufacturer in PDF format can be downloaded in this section.