Comparison of two methods of power amplifiers to achieve
Power amplifier circuit is an energy conversion circuit, requires distortion to the extent permitted and efficiently as large as possible for the load power, power amplifier tube operating current, voltage varies greatly, then transistor often work in large-signal or close to the limit state by state, with A, B, B class, and other work. In order to improve efficiency, made a push-pull amplifier circuit, amplifier tubes work status is set to B class, in order to reduce crossover distortion. Common audio amplifier circuit in connection with dual power supply form the main complementary push-pull power amplifier OCL (no output capacitor), single-supply complementary push-pull power amplifier OTL (output transformer-free), balance (bridge) and other non-transformer power amplifier BTL . As the amplifier tube to withstand high current, high voltage amplifier tube, therefore the protection and heat dissipation must be paid attention. PA can be discrete components, integrated circuits may also be achieved.
1 discrete components PA
Figure 1 is a discrete form of the DC circuit of the complementary symmetry OCL. By the differential amplification circuit, the voltage output level to promote and composite form. The negative feedback circuit into the DC circuit, because of the general power amplifier in the feedback capacitance, limits the low frequency response, in order to eliminate this adverse effect, only increasing feedback capacitance, but the larger capacitance will lead to circuit instability. The cancellation of the feedback capacitance circuit, solve the contradiction. Meanwhile, the introduction of radio-level resistance level of negative feedback, significantly improved the performance of this level and simplify the circuit. Class B output stage work in the state, not only for the efficiency, but also to ensure the work of state linear components. Difference in charge of magnification is equal to 200, two to be very little difference. Voltage amplification factor is equal to 80 to promote the tube.
Under these conditions, good performance power supply to provide power and bias, and finally to the whole circuit debugging. Can be measured: the current set input 20 mV, the output power> 12 W. The circuit should be noted that non-linear distortion and noise reduction, the final debugging more complex. However, the basic amplifier circuit only, it features a great room for expansion.
2 integrated power amplifier circuit
Now there are many excellent market integrated power amplifier chip, such as the dual op-amp NE5532, TDA2040, LM1875, TDA1514, etc.. TDA2040 power margin which is not, TDA1514 complex external circuit, so integrated power amplifier design used in LM1875.
Figure 2 is composed with the LM1875 integrated power amplifier, the open-loop gain of 26 dB, the amplification factor A = 20. One 20 kΩ, 1 kΩ resistor negative feedback network, two diodes for the protection diodes, output resistance and capacitance to form anti-high-frequency self-excited circuit, positive and negative ends of capacitors for power supply decoupling capacitor. If the output resistance load power> 10 W, with power management on the pressure drop 2 V, the output efficiency can be calculated as 66 2%, the biggest distortion voltage peak - to 25 3 V, the input signal voltage peak - peak 2 53 V. The remains of the pre-amplifier circuit, the waveform converter, power supply and protection circuits to be improved preamplifier can be used two NE5532 Typical application circuit; wave transformation complete with high-precision operational amplifier OP07; regulated power supply from the LM317 and LM337 composition; protect the circuit from the relay plus transistor circuit. The amplification circuit to simulate the main circuit board between the dual-core shielded cable should be used to prevent self-excitation interference. The amplifier circuit parameters to achieve a reasonable, relatively simple.
Comparison of two methods of power amplifiers to achieve
Comparison of two methods of power amplifiers to achieve
Power amplifier circuit there are many other forms, such as multi-level direct-coupled amplifier OCL, regardless of the power amplifier circuit to which type, should pay attention to pre-voltage amplification stage, power supply circuit design. Finally, we must pay attention as the work of the working point caused by temperature drift phenomenon, so as to appropriate compensation circuit to reduce the non-linear distortion and increase stability.
3 Conclusion
By the discrete components of the power amplifier, if the circuit is well chosen and appropriate parameters, components, excellent performance, good design and debugging, the performance is very good. Many high-quality amplifiers are discrete amplifiers. But as long as one part of a problem, then the performance will be lower than normal integrated amplifier. And in order not to overload, overcurrent, overheating and other damage to components, needs to be a complex protection circuit. Li component in the composition of PA in the transistor, diodes, resistors, capacitors and other components form the core of the circuit, with the freedom to adjust the room.
Integrated amplifier circuits mature, low-frequency performance, the internal design of complex protection circuit, can increase the reliability of its work, in particular, Ji Cheng thick device parameters stable condition and no adjustment, signal to noise ratio smaller and the circuit layout of a reasonable and simple external circuit, protection functional and heat sinks can also be applied to solve heat problems.