Public-Address Amplifier Isolation Without an Output Transformer
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Solution Overview
Problem
Existing high-impedance public-address systems require large-sized power amplifiers due to the need for output transformers to prevent ground current during lightning strikes, while maintaining isolation between transmission lines and ground potential.
Innovation Solution
A public-address system design that uses an isolation input means, such as a transformer or light-emitting and light-receiving devices, to isolate the power amplifying stage from ground potential, eliminating the need for an output transformer and allowing for a smaller power amplifier size by using a common potential point different from ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an output transformer is used to prevent large current flow during lightning strikes, then isolation from ground potential is improved, but the power amplifier becomes large-sized
Solution Approach 1:
The patent divides the isolation function into two separate stages: input-side isolation using a small isolation transformer and output-side isolation using a common potential point. This segmentation allows each stage to use minimal isolation components, eliminating the need for a large output transformer while maintaining complete isolation functionality.
Solution Approach 2:
The patent introduces a common potential point as an intermediary reference voltage level between the isolated power amplifier output and ground. This intermediary allows the power amplifier to operate with minimal isolation components while still preventing large current flow during lightning strikes, as the common potential point acts as a buffer.
2Reliability
If a transformer is used for isolation, then protection against lightning strikes is improved, but the device complexity increases
Solution Approach 1:
The patent segments the isolation requirement into input-side and output-side functions, allowing each side to use simple isolation components rather than requiring a complex single transformer. The input side uses a small isolation transformer while the output side uses a common potential point, reducing overall device complexity.
Solution Approach 2:
The patent extracts the essential isolation function from the traditional output transformer and distributes it across two simpler components: a small input isolation transformer and a common potential point reference. This extraction eliminates the need for the large, complex output transformer while maintaining protection functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design ensures isolation from ground potential, preventing large current flow during lightning strikes and enabling the use of smaller power amplifiers without the need for output transformers, thus reducing system size while maintaining necessary isolation and breakdown resistance.
Implementation Method 1
The isolation input means may be a transformer. The transformer has its primary winding connected between the two terminals of the audio signal source, and has its secondary winding connected to the two output-side terminals of the isolation input means.
Implementation Method 2
The isolation input means may include light-emitting means emitting light in accordance with an audio signal from the audio signal source
Implementation Method 3
light-receiving means providing an electrical signal in response to the reception of light from the light-emitting means
Data Source
AI summary
[Object]To downsize a power amplifier, while keeping isolation between a transmission line and ground potential.[Means to Realize Object]Two terminals (2a, 2b) of an audio signal source (2) are connected to an input of an isolation input circuit (6). An audio signal developed, being isolated from the input-side, between two output-side terminals (6a, 6b) of the isolation input circuit (6) are inputted to a power amplifying stage (12). The power amplifying stage (12) amplifies the audio signal and outputs it at a high voltage from two output terminals (12c, 12d) to a plurality of loudspeakers (22) without using an insulation transformer. Operating power is supplies to the power amplifying stage (12) from two power supply terminals (20c, 20d) of a DC power supply (14). One (6d) of the terminals of the insulation input circuit (6), one (12d) of the output terminals of the power amplifying stage (12) and one (20d) of the power supply terminals of the DC power supply (14) are connected together to provide a common potential point different from the ground potential.