Bridge Audio Amplifier

[moty22]

The datasheet of TDA2822M has circuit for bridge amp.
I corrected it as in the bottom drawing.
My point is that the inverting input of the opposite phase amp cannot be going to the inverting input of another amp, it has to go to the output of the first amp.
Come on experts! do your bit!

circuit with my correction

 

[audioguru]

The TDA2822M has built-in negative feedback resistors. With your modification then the voltage gains of the two amplifiers are not the same.

 

[Wade Hassler]

Have to quibble a little with calling that 'bridged'.. I'd expect a bridged amp to be able to pull both ends of the speaker from Vcc to Vss.
The circuit shown is a way of saving 40¢(?) worth of electrolytics by spending 52¢(1K/Digikey) for another TDA2822.
Frequency range is a bit wider and no DC in the speaker.

 

[audioguru]

The bridged amplifier circuit contains two power amplifiers. When the output of the first amplifier goes as high as it can then the output of the second amplifier goes as low as it can. Then the amplifiers alternate. The bridged amplifier produces almost 4 times the power than a single amplifier using the same power supply voltage and speaker impedance.
The speaker is connected directly to the outputs of both amplifiers. The amplifiers are on the same chip so that their output voltages match pretty well. Then there is no DC in the speaker so a coupling capacitor is not needed.

Like most audio power amplifiers, the outputs of the TDA2822M use emitter-followers so the output swings are not rail-to-rail but enough to do the job.

A TDA2822 without the "M" suffix is the same dual amplifier chip in a larger package. Then it can use a lower speaker impedance and/or a higher supply voltage to provide more output power than the little one without getting too hot.

 

[KeepItSimpleStupid]

To quickly understand bridging, two amplifiers are used and 1 is fed the non-inverted input and the other is fed the inverted input, so the output of one amp is 180 degress out of phase. The speaker output is then taken from the two output terminals. The common is not connected.

The voltage gain may have to change, but more importantly is that SOMETHING limits the output power. (V p-p available, R (the speaker Z) or I)

With P = (I^2)*R, I can limit the power. So, while any "bridge" configuration could double the voltage, I^2 available must be high enough to change the power assuming the same load.

 

[audioguru]

Each amplifier in a bridged amplifier that drives an 8 ohm speaker has a maximum output current the same as a single amplifier driving a 4 ohm speaker using the same supply voltage. Since the voltage swing in a bridged amplifier is doubled then the current swing is also doubled.