Bridge amplifiers

[epilot]

Hello,

can someone say me about BRIDGE (power) amplifiers?

i want to know the difference between it and a common amplifier too.

i saw a circuit about that amplifiers, it seems they are a kind of "perfect" amplifiers rather than common amplifiers, is this correct?

 

[Styx]

are you talking about class-D amplifiers? (and the D != Digital, it is just the nx letter in the amplifier saga)

Class A,AB,B,C,D,E,F,G...

https://en.wikipedia.org/wiki/Electronic_amplifier

Basically a Class-D amplifier utilises a H-bridge cct with very high switching freq (100s Khz) as well as dedicated filtering. THe advantage is the efficiency is extreamly good (they are used in mobile phones and mp3 players due to their efficiency and size).

 

[audioguru]

A bridge amplifier is actually two amplifiers with a speaker connected at their outputs like a bridge. The amplifiers have opposite polarity signals so the output of one goes positive when the output of the other goes negative.
An ordinary amplifier has a single output that swings from almost 0V to almost the positive supply, with a speaker capacitor-coupled to it.
A bridge amplifer doesn't need an output coupling capacitor and effectively doubles the voltage swing to the speaker, which also doubles the current resulting in about 4 times the power of an ordinary amplifier.

 

[Nigel Goodwin]

To be more exact, bridged amplifiers provide double the power into double the impedance - they provide EXACTLY the same total power as the two individual amplifiers could, just into a single load of a different impedance.

If they try and provide four times the output power the amplifiers will be destroyed - unless the amplifiers were previously running into double their rated load.

 

[Styx]

oops my bad. Server me right for dealing with H-bridge all day

 

[audioguru]

To be more exact, bridged amplifiers provide double the power into double the impedance - they provide EXACTLY the same total power as the two individual amplifiers could, just into a single load of a different impedance.

I was talking about using the same speaker.
Many car radio amplifier ICs can drive a 1.6 ohm or 2 ohm load but speakers usually have a minimum impedance of 4 ohms. With a 13.8V supply, these amps can supply 3.7W at low distortion singly into a 4 ohm speaker, or 13.5W when bridged. Nearly 4 times the power.

 

[bloki]

Both above posters are right. But a real question is why to use bridge configuration.
At certain supply voltage you can get a certain maximum output power because voltage swing is limited. Bridge amplifier doubles voltage swing and the consequence is four times greater output power than with a single amplifier. Of cause, such an amplifier must withstand double output current with the same load, compared to single amp.

Connecting existing amplifiers into bridge configuration is possible but limitation of max output current determines the minimal allowed load resistance. To get four times greater power at the same load the current limit must be twice as high as it is normal for max output power of single amplifier what is rather rare property. It is safe to use double load resistance, keeping in mind not to overload amplifier, but because of that the output power will be only doubled.

 

[Nigel Goodwin]

I was talking about using the same speaker.
Many car radio amplifier ICs can drive a 1.6 ohm or 2 ohm load but speakers usually have a minimum impedance of 4 ohms. With a 13.8V supply, these amps can supply 3.7W at low distortion singly into a 4 ohm speaker, or 13.5W when bridged. Nearly 4 times the power.

But at that the individual amps are rated into 2 ohms!, and NOT four ohms - with a bridged amp each half of the amplifier effectively drives half of the load, so for a 4 ohm load each speaker sees 2 ohms. Driving two 2 ohm speakers from the individual amps would provide exactly the same 13.5W, with exactly the same dissipation in the amplifiers.

 

[audioguru]

Yeah, the bridgeable car amp ICs are rated with a 2 ohm load individually, but most drive a 4 ohm speaker. When the amp is bridged then the 4 ohm speaker receives nearly 4 times the power.

 

[Nigel Goodwin]

Yeah, the bridgeable car amp ICs are rated with a 2 ohm load individually, but most drive a 4 ohm speaker. When the amp is bridged then the 4 ohm speaker receives nearly 4 times the power.

That's why I always specify twice the power into twice the impedance, that tells you EVERYTHING you need to know - just saying "4 times the power" is misleading, because it assumes you weren't loading the amplifier correctly in the original stereo situation.

You might as well say "8 times the power", and assume using 8 ohm speakers originally?.