IC Bridge Circuits

Thread Starter

Jeff Chriss

Joined Jul 17, 2022
1
Looking for LM386 Bridge circuit using electret mic for input. Confused about signal ground and DC power ground, seems to be different symbols.
 

MrChips

Joined Oct 2, 2009
27,137
I am not sure what you mean by LM386 bridge circuit.
LM386 is meant to be used as an amplifier to drive a loudspeaker.
A bridge circuit is usually used to balance sensors as in a Wheatstone bridge.

1661190644432.png
 

Irving

Joined Jan 30, 2016
3,132
Maybe this helps (from here)


A bridge circuit gives more output power as it doubles the voltage swing across the load. Signal ground and power ground are the same, but often differentiated to imply layout considerations.
1661190898337.png
 

DickCappels

Joined Aug 21, 2008
9,319
Looking for LM386 Bridge circuit using electret mic for input. Confused about signal ground and DC power ground, seems to be different symbols.
If the circuit is completely on one board, then the chassis ground and the earth ground can probably be connected.

If you post the schematic of which you write we can tell you for certain.
 

Audioguru again

Joined Oct 21, 2019
5,183
The LM386 Stereo Bridge Amplifier circuit in post #5 uses a 6V battery or a 9V external power supply. The schematic does not show the speaker impedance.
It uses three LM386 amplifier ICs.

The left and right amplifiers are connected out-of-phase that cancels bass sounds.
Assuming 8 ohm speakers, a left or right amplifier plus the center amplifier tries to double the voltage and current of a speaker connected to a single amplifier. LM386 amplifiers cannot do that.

The single amplifier maximum speaker output level is shown on the LM386 datasheet to be 6Vp-p when the supply is 9V.
The current for one output amplifier plus the center amplifier in the stereo bridge circuit tries to increase the speaker voltage and current but the amplifiers have losses that cause LM386 heating instead of increased speaker power. The actual speaker power is reduced in this terrible circuit.

The circuit designer says he is an electronics student and has poor English then maybe he cannot read the LM386 datasheet.
With a 6V battery and an 8 ohm speaker, a single LM386 produces only 0.25W in the speaker.
With a 9V supply and an 8 ohm speaker, a single LM386 produces only 0.56W in the speaker.
2W plus 2W is impossible. A 12V power supply will simply create smoke instead of speaker power.
 

MrSalts

Joined Apr 2, 2020
2,376
I am not sure what you mean by LM386 bridge circuit.
LM386 is meant to be used as an amplifier to drive a loudspeaker.
A bridge circuit is usually used to balance sensors as in a Wheatstone bridge.

View attachment 274473
A whetstone bridge is just one usage of the word "bridge" in electronics. See here for your introduction to bridged amplifiers - as AG says, the LM386 isn't a good amp for bridging.
https://en.m.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers
 

Audioguru again

Joined Oct 21, 2019
5,183
The low power LM386 amplifier is designed to use a 9V supply and an 8 ohm speaker. Then it produces 0.56W of speaker power and 0.56W of heating.
With a supply higher than 9V and a speaker impedance less than 8 ohms then its heating is massive.
I tried to calculate its output power and heating when it has two LM386 bridged amplifiers:
 

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