Complete collection of lm324 audio amplifier circuit

LM324 is a four-op amp integrated circuit. It is packaged in a 14-pin dual-in-line plastic package and its appearance is as shown in the figure. It contains four groups of identical operational amplifiers inside. Except for the shared power supply, the four groups of operational amplifiers are independent of each other. Each set of operational amplifiers can be represented by the symbols shown in Figure 1. It has 5 pins, of which "+" and "-" are the two signal input terminals, and "V+" and "V-" are the positive and negative power supplies. terminal, "Vo" is the output terminal. Among the two signal input terminals, Vi-(-) is the inverting input terminal, indicating that the signal at the output terminal Vo of the op amp is opposite to the bit of the input terminal; Vi+(+) is the non-inverting input terminal, indicating the signal at the output terminal Vo of the op amp. Same phase as this input. The pin arrangement of LM324 is shown in Figure 2

Because the LM324 quad operational amplifier circuit has the advantages of wide power supply voltage range, low static power consumption, single power supply use, and low price, it is widely used in various circuits. Its application examples are introduced below.

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LM324 as an inverting AC amplifier

See attached diagram for circuit. This amplifier can replace transistors for AC amplification and can be used for amplifier preamplification, etc. The circuit does not require debugging. The amplifier is powered by a single power supply, which is composed of R1 and R2 for 1/2V+ bias, and C1 is the vibration elimination capacitor.

The amplifier voltage amplification factor Av is only determined by the external resistors Ri and Rf: Av=-Rf/Ri. A negative sign indicates that the output signal is out of phase with the input signal. According to the value given in the figure, Av=-10. The input resistance of this circuit is Ri. Generally, Ri is equal to the internal resistance of the signal source, and then Rf is selected according to the required amplification factor. Co and Ci are coupling capacitors.

LM324 as non-inverting AC amplifier

see Attachment. Non-inverting AC amplifiers are characterized by high input impedance. Among them, R1 and R2 form a 1/2V+ voltage divider circuit, and the op amp is biased through R3. The voltage amplification factor Av of the circuit is also determined only by the external resistor: Av=1+Rf/R4, and the input resistance of the circuit is R3. The resistance of R4 ranges from several thousand ohms to tens of thousands ohms.

LM324 as AC signal three distribution amplifier

This circuit can divide the input AC signal into three outputs, and the three signals can be used for indication, control, analysis and other purposes respectively. The impact on the signal source is minimal. Because the input resistance of the operational amplifier Ai is high, the output terminal of the operational amplifier A1-A4 is directly connected to the negative input terminal, and the signal is input to the positive input terminal, which is equivalent to the situation of Rf=0 in the non-phase amplification state, so the voltage amplification factor of each amplifier is the same. is 1, which has the same effect as an emitter follower composed of discrete components.

R1 and R2 form a 1/2V+ bias. The voltage at the output terminal of A1 is 1/2V+ in static state, so the output terminals of the op amp A2-A4 are also 1/2V+. Through the DC blocking effect of the input and output capacitors, the AC signal is taken out to form three channel distribution output.

LM324 as active bandpass filter

Many spectrum analyzers of audio devices use this circuit as a band-pass filter to select signals in different frequency bands, and use the number of light-emitting diodes to light up on the display to indicate the amplitude of the signal. The center frequency of this active bandpass filter, the voltage gain Ao=B3/2B1 at the center frequency fo, the quality factor, 3dB bandwidth B=1/(п*R3*C) can also be determined according to the design Q, fo and Ao values ​​to find the parameter values ​​of each component of the bandpass filter. R1=Q/(2пfoAoC), R2=Q/((2Q2-Ao)*2пfoC), R3=2Q/(2пfoC). In the above formula, when fo=1KHz, C takes 0.01Uf. This circuit can also be used for general frequency selective amplification.

This circuit can also use a single power supply, just bias the positive input terminal of the op amp at 1/2V+ and connect the lower end of resistor R2 to the positive input terminal of the op amp.

LM324 should be used as a temperature measurement circuit

see Attachment. The temperature probe uses a silicon triode 3DG6, which is connected in the form of a diode. The temperature coefficient of the emitter junction voltage of a silicon transistor is about -2.5mV/℃, that is, for every 1 degree increase in temperature, the emitter junction voltage will decrease by 2.5mV. The operational amplifier A1 is connected in a non-phase DC amplification form. The higher the temperature, the smaller the voltage drop of the transistor BG1, the lower the voltage at the non-inverting input terminal of the operational amplifier A1, and the lower the voltage at the output terminal.

This is a linear amplification process. By connecting the measurement or processing circuit to the A1 output terminal, the temperature can be indicated or other automatic controls can be performed.

LM324 should be used as comparator

When the feedback resistance of the op amp is removed, or when the feedback resistance tends to infinity (i.e. open-loop state), theoretically, the open-loop amplification factor of the op amp is also infinite (actually very large, such as the LM324 op amp open loop The amplification is 100dB, which is 100,000 times). At this time, the op amp forms a voltage comparator, and its output is either high level (V+) or low level (V- or ground). When the positive input terminal voltage is higher than the negative input terminal voltage, the op amp outputs a low level.

In the figure, two operational amplifiers are used to form an upper and lower voltage limit comparator. The resistors R1 and R1ˊ form a voltage dividing circuit to set the comparison level U1 for the operational amplifier A1; the resistors R2 and R2ˊ form a voltage dividing circuit to set the voltage dividing circuit for the operational amplifier A2. Set comparison level U2. Input voltage U1 is added between the positive input terminal of A1 and the negative input terminal of A2 at the same time. When Ui > U1, the operational amplifier A1 outputs high level; when Ui

If U2 > U1 is selected, when the input voltage is within the range [U2, U1], the LED lights up. This is a "window" voltage indicator.

This circuit is used in conjunction with various sensors. With slight modifications, it can be used for double-limit detection, short circuit, open circuit alarm, etc. of various physical quantities.

LM324 should be used as a monostable trigger

See attached picture 1. This circuit can be used in some automatic control systems. Resistors R1 and R2 form a voltage divider circuit to provide bias voltage U1 for the negative input terminal of op amp A1 as a comparison voltage reference. In static state, capacitor C1 is fully charged, and the voltage U2 at the positive input terminal of op amp A1 is equal to the power supply voltage V+, so A1 outputs a high level. When the input voltage Ui becomes low level, the diode D1 is turned on, and the capacitor C1 is rapidly discharged through D1, causing U2 to suddenly drop to the ground level. At this time, because U1>U2, the op amp A1 outputs a low level. When the input voltage becomes high, the diode D1 cuts off, and the power supply voltage R3 charges the capacitor C1. When the charging voltage on C1 is greater than U1, U2>U1, the A1 output becomes high level again, thus ending a monostable trigger. Obviously, increasing U1 or increasing the values ​​of R2 and C1 will increase the monostable delay time, and vice versa will shorten it.

If diode D1 is removed, this circuit has a power-on delay function. When it is first powered on, U1>U2, the output of op amp A1 is low level. As capacitor C1 continues to charge, U2 continues to increase. When U2>U1, the output of A1 becomes high level.