Use of power amplifier IC

Before the 1980s, power amplifiers with only a few watts of output power must use discrete originals. After the 1980s, China began to develop low-power amplifier ICs, but due to the poor performance indicators of these amplifiers, especially the poor reliability, soon Replaced by power amplifier ICs produced abroad. The HA1392 and TA7240 produced in Japan were once very common power amplifier ICs used in the 1980s. The output power of HA1392 and TA7240 are only 5-6 watts. The upper limit of the operating frequency of HA1392 is lower. The power supply will be damaged immediately after reverse connection. The peripheral circuit design is more difficult, and the mute control is susceptible to external interference and misoperation. The TDA2030A developed and produced by ST's power amplifier IC in the early 1980s is considered to be a relatively good power amplifier IC, and its output power reaches more than 14W. Although SGS has produced TDA2040, TDA2050, and power amplifier IC on the basis of TDA2030A to make the output power above 24W, but because their power supply range is only + -22V, if they use unregulated rectified and filtered DC power, they actually It can only output 12W power to a 4 ohm load. The LM1875 power amplifier IC developed and produced by NS in the United States in the 1980s is twice as high as the output power of the TDA2030A power amplifier IC produced by SGS. The reason is that his power supply adapts to a range of + -30V. If a regulated filter DC is used, TDA2030A and The LM1875 can actually output 24W sine wave effective power to a 4 ohm load under + -18V power supply conditions. As an early-developed power amplifier device, neither the TDA2030A nor the LM1875 has a mute control function, and the ability to suppress power ripple is not strong enough. Shortly after the launch of TDA2030A by STMicroelectronics, Philips in the Netherlands also developed and produced a TDA1521Q bi-power amplifier IC with the same performance indicators. The power supply range of this power amplifier IC is also + -22V, which can simultaneously output two 4 ohm loads. 12w power. Since the TDA1521Q has made the negative feedback circuit that determines the magnification factor inside the IC, it is easier to use. Since then, the Philips company in the Netherlands has launched a model TDA1514A high-performance power amplifier IC, the product information says that it can output 40W of power. However, it has been proved in practice that under the condition of using a regulated DC power supply, the TDA1514A can only work with a voltage of + -18V, and the effective power output to a 4 ohm load is 24W. If the voltage is raised to + -20V, TDA1514A Overload protection will occur, and the overload protection action performed will appear as a half-wave cut-off output. In this way, people only design the working voltage of TDA1514A to be the same as LM1875.
Before the 1990s, the output power of power amplifier ICs provided by electronic device manufacturers was actually below 30W. After more than 10 years of hard work, both the US NS company and STMicroelectronics have launched a power amplifier IC with a power exceeding 30W during the 1990s. Among them, LM3876, LM3886 are the representative works of the US NS company, TDA7293, TDA7294, etc. It is a representative work of STG SGS. These power amplifier IC chips have a small installation volume and multiple security protection functions, which are very easy to use *. But at the same time, it is precisely because the power amplifier IC chip needs a lot of safety protection functions such as overheating, overcurrent, overvoltage, and overpower consumption. Manufacturers may design the internal protection circuit of the power amplifier IC chip because of the detection used. The way is too sensitive or immature, and some problems are not perfect. The manufacturer did not write these defects in the product introduction, although it may not want their product sales to be affected, but the more reason is that they may not have discovered these defects themselves, but need users to use the process, Feedback the discovered problems to the manufacturers, who will then improve and develop new devices. For example, the audio engineer of NS company in the United States recommended to the author to use their power amplifier IC. Among them, there is a model LM4701. This power amplifier IC is said to replace the LM1875. It has a mute control function and the output power is higher than that of the LM1875. However, the actual use proves that the LM4701 can work normally when driving a 4 ohm load, and the power supply voltage that does not cause false protection actions cannot exceed + -20V, and the maximum output power is only 20W. If the power supply voltage exceeds + -20V, for example: + -22V, the output power will not increase, the normal output power of the low-frequency band below 100HZ will be reduced to only 10W, although under the + -26V regulated power supply, LM4701 It can output 25W power to 8-ohm load, but because its power supply range is only + -32v, when using unregulated DC power supply, the LM4701 can output less than 20W to the 8-ohm load. Another example: TDA7264 bi-power amplifier IC produced by STMicroelectronics, the data shows that his maximum working voltage is + -25V, the maximum working current is 4A, which is better than the performance index of TDA2030A (the maximum working voltage is + -22V, the maximum working The current is 3.5 A) to be higher. However, the actual use proves that the TDA7264 can work with a 4 ohm load, and the power supply voltage that does not cause malfunctions cannot exceed + -15V, and the corresponding output power is only 2 X 12W. In addition, the heating temperature on the device when the TDA7264 is working (The test point is placed on the IC metal sheet) It should be kept below 70 degrees. Otherwise, the internal overheating protection circuit of the TDA7264 will have a cumulative effect due to the IC operating at a higher heating temperature, and the "soft protection" will appear after 30 minutes of continuous operation, but the power it can output falls below 1/4 of the normal value. . Originally, the ideal overheating protection function should be to turn off the output when the temperature of the power amplifier IC reaches the maximum allowable value, and resume the output when the temperature of the power amplifier IC cools to a few degrees lower than the maximum allowable temperature. After TDA7264 works, the heating temperature reaches 110 degrees in a short period of time without overheating protection. The working condition is good. People will mistakenly think that TDA7264 has good temperature characteristics and reduce the heat dissipation requirements for it. Although the LM1875 power amplifier IC produced by American ns Company in the 1980s does not have a mute function, its internally designed overheat protection function is close to ideal requirements, so it continues to be widely used by audio manufacturers until today. However, the LM3875 and LM3886 high-power amplifier ICs produced by American NS in the 1990s have been disappointing in the performance of overheat protection! Especially for the power amplifier IC with ceramic insulation package, due to its poor thermal conductivity, the LM3875 cannot continuously output even a sine wave rated power of more than 10W when driving a 4 ohm load. Even if the load is changed to 8 ohms, the LM3875 with ceramic insulation package can normally output a rated power of 30W sine wave and the noise can only appear for a few seconds. Similarly, the LM3875 with ceramic insulation package can normally output a rated power of 40W sine wave when driving a 4 ohm load. The time when the LM3875 can normally output a sine wave rated power can only be maintained for a few seconds and clutter begins to appear. It is necessary to use metal encapsulated thermally conductive devices and keep the temperature on the metal plate of the power amplifier IC not to exceed 85 degrees. The LM3875 and LM3886 can output 30W and 50W sine wave power to a 4 ohm load for a normal long-term output. Therefore, when people use LM3875, LM3886 and other high-power IC devices, they must be equipped with a heat sink large enough. At the same time, the thickness of the heat conductive sheet used for the insulation of the metal sheet of the power amplifier IC should be as thin as possible, not exceeding 0.3mm, so as to ensure that the temperature difference between the power amplifier IC and the heat sink is only a few degrees.
The TDA2030A power amplifier IC produced by STMicroelectronics in the 1980s is slightly worse than the LM1875 produced by the US NS company in overheat protection. Its characteristic is that the output signal waveform will appear on the output signal waveform when the heating temperature on the metal plate of the power amplifier IC exceeds 105 degrees. Clutter. When the heating temperature of the LM1875 power amplifier IC is lower than the maximum allowable value, the output signal waveform always remains normal. Only when the heating temperature on the IC metal sheet reaches 115 degrees, the LM1875 power amplifier IC will turn off the output /. The heating temperature on the metal sheet of the TDA2030A power amplifier IC also has to be turned off when it reaches 115 degrees, so he has an unstable working temperature section, but this temperature section is already a very high temperature. , Has no obvious effect on use. What is gratifying is that the TDA7293, TDA7294, TDA7295 and other power amplifier ICs launched by STMicroelectronics in the 1990s can achieve 50W of actual power, and they have done very well in overheat protection. When the heating temperature of the power amplifier IC is lower than the maximum allowable value, the output signal waveform keeps the normal and good. Only after the temperature on the IC chip of the power amplifier reaches 115 degrees, they can be turned off. Compared to other high-power amplifier ICs, TDA7293 produced by STMicroelectronics SGS,
TDA7294 and TDA7295 are indeed the best among them. Proved by actual use: the static output background noise voltage of these power amplifier ICs is not more than 0.25Mv, and the signal-to-noise ratio when outputting 1W power on a 4 ohm load is already greater than 75Db, so 50W power is output at full power on a 4 ohm load The signal-to-noise ratio at the time will be as high as 95Db. With a good performance amplifier IC, people make high-level Hi-Fi audio systems and high-level multi-channel home theater systems by themselves.
Note: (This article comes from the article of electronic production and Cheng Wenping. The author thinks it is good, and I sorted it out so that friends who like power amplifier ICs can use this article to make friends have a deeper understanding of power amplifier ICs. For reference.)

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