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I am working on an Active Noise Reduction project for a headset using Codec ADAU1772 from AD. There are two inputs, one of which is feedback mic. connected to AIN0, second is INT+ (Intercom or music) connected to AIN1. I take both inputs directly to the Codec for filters and EQ. Then, the Codec drives the 50ohm speaker with LP (Left Positive, Pin 22) and LN (Left Negative, Pin 21) differentially. The complete system works with external power (V+, 5V to 28V, typically 24V). The schematic is below.

enter image description here

For safety reasons, during a loss of power, the headset user should not lose the intercom signal. How can I manage this situation? I need to build a secondary driving circuit to understand a power loss and drive (not differentially) the Speaker automatically when it happens. Can a relay solve it, or transistors, etc.?

INT+ signal has enough power to drive the speaker.
VCC, VCCIO = +3V3
U1 = EEPROM
U3 = Trigger
U4 = Power Converter
U2 = ADAU1772 Codec

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    \$\begingroup\$ during [an interruption] of power, the headset user should not lose the intercom signal Whatever not lose the intercom signal means specifically, for an electric gizmo to keep working during a significant interruption of its primary supply of power, you need some backup, often battery. Uninterruptible Power Supply means mains power to same voltage&frequency more often than not. \$\endgroup\$
    – greybeard
    Commented Oct 17, 2023 at 9:02
  • \$\begingroup\$ @Firat Dagkiran. Can the intercom signal drive the speaker(s) without any amplification directly ? You need to work this out if it's indeed even possible to drive the speakers directly without it being processed by the codec. If the intercom signal cannot drive the headset speakers then there's no point in even trying to do what you want to do, and you'll need some temporary and infallible back-up power supply source like already mentioned. However if the intercom signal is strong enough to drive the speaker(s) then maybe there's a solution for what you're wanting to do ... \$\endgroup\$
    – citizen
    Commented Oct 19, 2023 at 12:07
  • \$\begingroup\$ Do you have any further details on the intercom signal, like its nominal rms voltage and peak voltage, what impedance is it ment to drive, etc. where is it coming from and what was it intended to drive ? You'll need to add this info to your question for clarification. \$\endgroup\$
    – citizen
    Commented Oct 19, 2023 at 12:10
  • \$\begingroup\$ INT+ (Intercom Signal) can drive 50ohm speaker. It has a 3Vpeak voltage level with a 500mW power. Regarding the backup power supply, I have nothing to do with it. I only design the headset electronics; power comes from the customer intercom system. Think about a headset connected to intercom systems that take inputs: power and intercom (INT+). \$\endgroup\$
    – Firat Dagkiran
    Commented Oct 21, 2023 at 23:25

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