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Principles and application of the op amp LM324

Published on Mar 14 2011 // Device application circuits

Principles and application of the op amp LM324 1

In this paper, high-performance integrated LM324 quad op amp parameters, the practical circuit design, discusses the circuit.
LM324 is a quad op amp integrated circuit, which uses 14-pin dual in-line plastic package, shape as shown. It contains four sets of the internal op amp in exactly the same form, in addition to power sharing, the four independent amplifier. Operational amplifier for each group of symbols shown in Figure 1 can be used to indicate that it has 5 leads to the foot, which "+","-" two signal input, "V +", "V-" is positive, negative power supply side, "Vo" for the output. Two signal input in the, Vi-(-) for the inverting input, said operational amplifier output Vo of the signal with the input bit contrary; Vi + (+) for the same phase input, said operational amplifier output Vo of the signal phase with the same input. LM324 pinout shown in Figure 2

Principles and application of the op amp LM324 2

The LM324 quad op amp circuit has a supply voltage range, the static power consumption, power usage can be a single, low cost, etc., is widely used in various circuits. Here are examples of its application.
LM324 exchange for inverting amplifier
Circuit See attached map. This amplifier can be amplified to communicate instead of transistors, amplifiers can be used for pre-amplification. Circuit without debugging. Single supply amplifier, by R1, R2 bias the composition 1/2V +, C1 is the capacitance of vibration.

Principles and application of the op amp LM324 3

Amplifier voltage gain Av only by the external resistor Ri, Rf decision: Av =- Rf / Ri. Minus the output signal and input signal phase contrast. Values given by the figure, Av =- 10. The circuit input resistance Ri. Under normal circumstances the first to take the signal source resistance Ri are equal, then the requirements of the selected magnification Rf. Co and Ci is the coupling capacitance.
LM324 amplifier for communication with the phase
See attached map. Phase AC amplifier with high input impedance characteristics. One of R1, R2 voltage divider composed of 1/2V +, R3 of the op amp through the bias. Circuit voltage gain Av is only determined by external resistor: Av = 1 + Rf/R4, the circuit input resistance R3. R4 resistance range for thousands of ohms to tens of thousands of ohms.

Principles and application of the op amp LM324 4

LM324 three distribution amplifiers for ac signal
This circuit can be input AC signal into three outputs, three signals can be used to indicate, respectively, control and analysis purposes. The minimal impact on the signal source. Ai due to op amp input resistance, op amp A1-A4 are the output directly to the negative input, the signal input to positive input terminal, the equivalent of state-phase amplified the situation Rf = 0, so the voltage amplification factor of the amplifier are 1, with the discrete components of the emitter follower same effect.

 Principles and application of the op amp LM324 5

R1, R2 form 1/2V + offset, static A1 output voltage 1/2V +, so the op amp output of A2-A4 also 1/2V +, by blocking input and output capacitance effect, remove the AC signal, the formation of three Road distribution output.
LM324 for Active Band Pass Filter
Spectrum analyzer in many audio devices are using this circuit as a band-pass filter, to select different frequency signal, the display on the use of LED lights to indicate the number of the signal amplitude. The active center frequency of bandpass filter, At the center frequency fo voltage gain Ao = B3/2B1, quality factor, 3dB bandwidth of B = 1 / (п * R3 * C) can also be designed to determine Q, fo, Ao values, to calculate the band-pass filter component values. R1 = Q / (2пfoAoC), R2 = Q / ((2Q2-Ao) * 2пfoC), R3 = 2Q / (2пfoC). Where, the time when the fo = 1KHz, C take 0.01Uf. This circuit can be used for general frequency-selective amplification.

Principles and application of the op amp LM324 6

This circuit can also use a single power supply, just the positive input of op amp bias resistor R2 in the bottom of 1/2V + and received both the positive input of op amp.
LM324 be used as a temperature measuring circuit
See attached map. Temperature probe with a silicon transistor 3DG6, it connected as diodes form. Silicon transistor emitter voltage temperature coefficient is about-2.5mV / ℃, the temperature rise of 1 degree each, varying emitter voltage drop 2.5mV. A1 amplifier connected in phase to enlarge the form of direct current, the higher the temperature the smaller the transistor BG1 pressure drop, the op amp inverting input A1 lower the voltage, the voltage output is also lower.

Principles and application of the op amp LM324 7

This is a linear amplification process. Measured in the A1 output termination or processing circuit, the temperature can carry out instructions or other automatic control.
Be used as a comparator LM324
When removed when the op amp’s feedback resistor, or the feedback resistor tends to infinity (ie, open-loop state), theoretically, that the op amp’s open loop for infinite magnification (actually a lot, such as the LM324 op opening Central magnification 100dB, only 10 times.) At this point they form an op amp voltage comparator, the output is not as high (V +), is low (V-or ground). When the positive input voltage is higher than the negative input voltage, the op amp output low.

 Principles and application of the op amp LM324 8

Photo op amp used in the composition of two upper and lower limits of a voltage comparator, resistor R1, R1

Principles and application of the op amp LM324 9