Oscillator circuit composed of LM386
LM386 is a low-power audio amplifier integrated circuit. It adopts 8-pin dual-in-line plastic package. The working voltage is 4V-15V. When the power supply voltage is 12V, the output power of 300mW can be obtained on an 8Ω load. Various oscillators can be easily made with LM386.
1. Minimal oscillator
Figure 1 The simplest oscillator circuit diagram
As shown in 1, connect the output end of LM386 and the non-inverting input end with a piezoelectric ceramic plate HTD, and the amplifier forms positive feedback and oscillates. Here HTD is both a feedback capacitor and a sounding device.
Component parameters in the figure: D1~D4 are 1N4001, C1=220pF, HTD is a piezoelectric ceramic sheet with an acoustic cavity
2. Intermittent oscillator
Figure 2 Circuit diagram of a intermittent oscillator
As shown in Figure 2, LM386 and C3, C4 and loudspeaker form a simple oscillator. RP and C2 make this oscillator produce intermittent oscillation. After turning on the power supply, because the initial terminal voltage of C2 is zero, the LM386 does not work, and the power supply charges C2 through RP. When the charging voltage of C2 is higher than a certain value, the LM386 oscillator starts to vibrate. With the continuous increase of the amplitude, the current consumption of the oscillator is also increasing. This current flows through RP, and its voltage drop on RP is also increasing. If it is too large, the voltage of pin 6 of the power supply terminal of LM386 will drop continuously. Eventually the LM386 could not work and the oscillator stopped. The power supply is charged to C2 again through RP, so that the voltage of the C2 terminal rises. When the voltage of the C2 terminal rises to a certain value, the LM386 oscillator starts to vibrate again, and this cycle works, causing the oscillator to generate intermittent oscillation, and the speaker emits “beep, beep, beep…the sound of…
Component parameters in the figure: D1~D4 are 1N4001, C1=C3=220μF, C2=47μF. C4=0.01μF, RP=4.7K.
3. Electronic organ
Figure 3 Electronic organ circuit diagram
Figure 3 is a simple electronic organ circuit. At the 3 pin of LM386, the integrated circuit has a built-in 10KΩ resistor to ground. This built-in resistor and ten scale resistors such as RP1~RP10 constitute the timing resistor of the oscillator. C2 is the timing capacitor. Adjusting the value of RP1~RP10 can make the speaker sound from the low octave “1.2.3” to the high octave “1.2.3” in sequence, and KI~K10 are the key switches.
Component parameters in the figure: Cl=C3=220μF.C2=2200μF, RP1~RP10 are 85K adjustable electric anodes
4. Square wave oscillator
Figure 4 Square wave oscillator circuit diagram
Figure 4 shows a square wave oscillator composed of LM386, R1 is a timing resistor. C2 is a timing capacitor. R2 and R3 provide voltage bias for the non-inverting input terminal of LM386. After the power is turned on, since the voltage of the C2 terminal cannot be changed suddenly, the 2-pin of the inverting input terminal of the LM386 is set to a low level, and the 5-pin is the midpoint of the OTL output stage inside the amplifier. It is 1/2Voc when it is static. After dividing the voltage, it is supplied to the 3rd pin of the non-inverting input terminal. Obviously, the potential of this pin is higher than that of the 2nd pin. Therefore, pin 5 outputs a high level. This high level is charged to C2 through R1. When the voltage of C2 terminal is higher than the potential of pin 3, pin 5 outputs a low level. C2 is discharged to pin 5 through R1. When C2 is discharged, the potential of pin 2 drops and is lower than the potential of pin 3. Pin 5 outputs a high level again. This cycle works, the circuit oscillates, and the oscillating signal pushes the speaker to sound through C3.
Component parameters in the figure: C1=C3=220μF, C2=0.33μF.R1=22K, R2=1K.R3=9.4K.
5. Sine wave oscillator
Figure 5 Sine wave oscillator circuit diagram
Figure 5 is a sine wave oscillator made of LM386. The circuit adopts the Wen’s bridge oscillation method, and the distortion coefficient of the output signal is extremely low. The small electric ball H and the resistor R3 form a negative feedback circuit, which keeps the amplitude of the oscillator output signal stable and has low distortion. When the values of capacitors C1 and C2 are the same, the oscillation frequency of the circuit can be obtained by the formula f=1/2C1 R1R2, and the sine wave frequency is 1kHz when using the data shown in the figure. In actual production, H can choose 3V, 15mA small electric beads.