push-pull amplifier

* Actual photo! [image.png] * The input interface is a 3.5MM headphone interface, and the output interface is an ancient lotus audio interface. These two components are not available in Lichuang Mall and can be purchased on Taobao, but the general packaging styles are different, so when making your own boards, pay attention to the packaging of the purchased components first, and then change them before making the board.
* This project is a push-pull power amplifier based on MOS tubes IRF630 and IRF9630, which can drive 8Ω 5W speakers.
* Use 7815 and 7915 to build a positive and negative 15V power supply, and add LED lights to each power supply. After testing, it can output normal positive and negative 15V voltage.
* Use dual-channel operational amplifier NE5532 to build a voltage following circuit. When the circuit is working, you can see that the output signal of the voltage follower is no different from the input signal, which proves that the voltage follower isolates the front and rear stage circuits to ensure that the input voltage is not disturbed. Works perfectly fine.
* Use the other channel of the dual-channel operational amplifier NE5532 to build a non-inverting proportional amplifier circuit. The amplification factor is adjusted by adjusting the size of the feedback resistor. When the circuit is working, by adjusting the feedback resistor, you can see that the amplification factor can be adjusted. The amplification factor can theoretically be adjusted to 100 times, allowing the output amplitude of the push-pull circuit to reach the maximum voltage of the power supply. In actual debugging, because the phenomenon was too obvious, the magnification was only increased to more than ten times.
* Use MOS tubes IRF630 and IRF9630 with opposite polarities to build a Class A and B push-pull amplifier circuit. The two tubes are turned on alternately to achieve power amplification. When the circuit is working, the output power of each power supply can reach more than 5W, so the final output power of the push-pull amplifier circuit can reach more than 10W.


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-After completing the initial power amplification target, certain performance improvements were made.

* After the circuit has been running for a certain period of time, the MOS tube will heat up significantly due to the power consumption in the MOS tube. When the temperature rises, the turn-on voltage of the MOS tube will change, resulting in crossover distortion. In this project, I used the triode compensation method to compensate for the crossover distortion to a certain extent. The triode and MOS tube are coupled through a heat sink. When the MOS heats up, the triode heats up at the same time, and the voltage drop changes, which in turn causes the bias voltage of the MOS tube to change. Temperature compensation can be achieved by simply selecting a suitable transistor. However, since the transistor voltage drop and the MOS tube turn-on voltage change are not completely consistent, the compensation cannot be perfect.


* The output power of the push-pull circuit is very large and may burn the speaker. Therefore, a power dissipation resistor is added to the output end to dissipate excessive power. If the current is too large, the power resistor can dissipate the excess power. Use higher power cement resistors for this purpose.


* Since the load is a speaker, it has the characteristics of inductive load and capacitive load. After entering the circuit, it will have an impact on the circuit output. Therefore, the output sound quality will have some distortion. By consulting the information, add phase compensation components to the output circuit, as shown below. Among them, L1/R15 is used to offset the capacitive component, and C9/R16 is used to offset the inductive component. By actual measurements, the sound quality has improved.