Design issues of positive and negative power supplies for power amplifiers

zpccx

Design issues of positive and negative power supplies for power amplifiers [Copy link]

[attach]336807 [/attach] As shown in the figure, the power supply voltage of the power amplifier is ±12V, the input voltage is Vin=-4V ~ +4V, the gain G is set to 1.5, the output voltage Vout=-6V ~ +6V, the load is a pure resistor, and the resistance value is RL=1.5Ω, so the output current of the power amplifier is about Iout= -4A ~ +4A. When the input voltage of the power amplifier is +4V, the corresponding output voltage is 6V, and the output current is about +4A. At this time, the power on the load is 4x4x1.5=24W. The tube voltage drop of the output stage of the power amplifier is Vce=12V-6V=6V, so the power dissipation of the power amplifier = 6V x 4A =24W, The load power plus the power dissipation of the amplifier equals the power provided by the power supply (at this time, it is powered by +12V, and the tube connected to -12V is not conducting), that is, 24W+24W=48W. In summary, the +12V power supply should be able to provide more than 48W of power. Similarly, when the input voltage is -4V, the output voltage is -6V, and the calculated -12V power supply power should also be greater than 48W. My doubts are as follows: 1. The load current is as high as 4A, so should the ±12V power supply be able to withstand a current greater than 4A? 2. After looking around for LDOs, I found that there are positive voltage LDOs that can withstand a current of more than 4A, but there are no negative voltage LDOs that can withstand a current of more than 4A. Can 4 1A current LDOs be connected in parallel, so that a total of 4A can be provided to the -12V power pin? I used TINA to simulate it, and it is possible, but I don’t know if this is done in reality. 3. Is there a chip that can convert negative voltage and provide a current greater than 4A? 4. What is the best way to design a power supply for a power op amp with positive and negative rails and high current?

cruelfox

Why do we need to use a regulated power supply to power a high-power op amp? If its PSRR is sufficient, there is no need to add an LDO.

maychang

1. The load current is as high as 4A, so should the ±12V power supply be able to withstand a current greater than 4A? If the power amplifier is continuously working at full load, for example, the power amplifier output is used to drive the ultrasonic transducer to work continuously, then the ±12V power supply should be able to continuously withstand a current greater than 4A. If the power amplifier is not working continuously, for example, its output is used to drive the speaker to produce music or speech signals, then because music and speech are not continuously working at full load, the power supply only needs to withstand a peak current greater than 4A, and most of the time its current is less than 4A, and the heat dissipation capacity of the power supply can be slightly reduced.

maychang

2. After searching for LDOs, I found that there are positive voltage LDOs that can withstand currents above 4A, but there are no negative voltage LDOs that can withstand currents above 4A. Can four 1A current LDOs be connected in parallel to provide a total of 4A for the -12V power pin? Power amplifiers usually do not have very high requirements for power supply stability, and it is not necessary to use linear voltage regulator chips to supply the power amplifier's current. Even if you want to use a regulated power supply to power the power amplifier, you can also use a switching power supply. Today's switching power supplies have reached a fairly high level in terms of stability and ripple, and there is no problem in supplying power to audio power amplifiers.

maychang

4. How to design a better power supply for this kind of power amplifier with positive and negative rails and high current? At present, a switching power supply can be used.

chunyang

LDO is not suitable for high-power applications. Conventional three-terminal voltage regulators can be used. However, power amplifiers generally do not require voltage regulation. It is sufficient to have sufficient power reserve. Note that not all series voltage regulator chips are LDO. LDO specifically refers to low-voltage dropout series voltage regulator chips. Do not use the term indiscriminately. If you really need a voltage regulator, then the 7812/7912 5A type will do. Note that its package and model suffix are different from the ordinary 1A type. The 78 and 79 series usually refer to the 1A output type when the model suffix is ignored.

olive888

Happy holidays to the host! Wish you all the best in the new year

zpccx

chunyang posted on 2017-12-28 16:30 LDO is not suitable for high-power applications. A conventional three-terminal voltage regulator can be used. However, power amplifiers generally do not require voltage regulation. It is sufficient for the power reserve to be sufficient. Note...

Thank you, but I did not find the 5A version. . .

chunyang

zpccx posted on 2018-1-3 22:48 Thank you, but I didn’t find the 5A version. . .

For example, 78H12.

zpccx

chunyang posted on 2018-1-4 00:09 For example, 78H12.

There is no negative voltage

chunyang

zpccx posted on 2018-1-5 16:05 There is no negative voltage

79H12.