TPA3245 series amplifier problem

asd2996

TPA3245 series amplifier problem [Copy link]

I need help. For class D amplifiers like tpa3245, the power supply is +24v and there is no negative power. What is the input signal range? The manual says it is positive and negative. How can negative amplification be achieved without a negative power supply?

maychang

I didn't read the data carefully enough. The input clearly has a coupling capacitor.

asd2996

maychang posted on 2020-8-1 11:50 I didn't read the information carefully enough. The input clearly has a coupling capacitor.

I don't quite understand what the specific function of this capacitor is. Thank you.

asd2996

Describe it more clearly. As shown in the figure, the conventional Class D amplifier has a dual power supply of positive and negative electricity.


Now I want to use the tpa3245 integrated Class D amplifier chip. This chip is powered by a single power supply, only +24v power supply.


The input signal is also positive and negative,

without negative electricity. How does it work? How to amplify the negative half-axis voltage?

maychang

asd2996 posted on 2020-8-1 14:16 I don't quite understand what the specific function of this capacitor is. Thank you

I don’t know if you have studied “Analog Circuits” or similar courses. As long as it is an “Analog Circuits” textbook, it will talk about discrete triode amplifier circuits, such as Kang Huaguang’s “Basics of Electronic Technology. Analog Part. (Kang Huaguang. 5th Edition)”. In the explanation of Figure 4.3.7 on page 124 of the book, there is a description of this capacitor.

maychang

asd2996 posted on 2020-8-1 14:16 I don't quite understand what the specific function of this capacitor is. Thank you

Some textbooks say that the function of capacitors is to "pass AC and block DC". This is not accurate, but it can be applied in the figure on the second floor. The capacitor in the red box removes the DC component of the four signal terminals from INPUT_A to INPUT_D. The signals on the 5, 6, 16, and 17 pins of the chip are actually the AC component of the signal on the terminal plus the DC component of the chip's internal bias.

xiaxingxing

maychang posted on 2020-8-1 11:50 I didn't read the information carefully enough. The input clearly has a coupling capacitor.

After the signal at the input is blocked by the DC blocking capacitor, it is still an AC signal centered on GND (0V). After entering the amplifier, there is still a negative signal? Do you mean that the amplifier adds a positive DC bias to the input signal?

maychang

xiaxingxing posted on 2020-8-1 15:46 After the signal at the input end is isolated by the DC isolation capacitor, it is still an AC signal centered on GND (0V). After entering the amplifier, there is still a negative signal...

"Senior, do you mean that the amplifier adds a positive DC bias to the input signal?"

Yes. The chip must have internal DC bias for pins 5, 6, 16, and 17.

maychang

xiaxingxing posted on 2020-8-1 15:46 After the signal at the input end is isolated by the DC isolation capacitor, it is still an AC signal centered on GND (0V). After entering the amplifier, there is still a negative signal...

Some power amplifier chips use a single power supply and allow negative input, such as LM386. The input of this chip can be cut off from DC without capacitors. However, the input of this chip uses a PNP bipolar transistor, which only allows a very small input amplitude. The LM386 only allows a maximum negative 0.4V. However, this is not the case with TPA3245, whose input amplitude can reach 7V.

maychang

xiaxingxing posted on 2020-8-1 15:46 After the signal at the input end is isolated by the DC isolation capacitor, it is still an AC signal centered on GND (0V). After entering the amplifier, there is still a negative signal...

The LM386 input stage circuit is similar to the LM358 op amp, using a PNP bipolar transistor. The LM358 op amp also allows the input to be negative, but only up to about negative 0.3V.