AC Attenuation Circuit Using PWM Control and Isolation

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Solution Overview

Problem

Existing AC load protection circuits face challenges in efficiently managing excessive power, including high costs due to the use of depletion MOSFET devices, slow response times of electromechanical relays, and the need for multiple system controllers for multi-channel systems, which can lead to harmonic distortion and complex communication schemes.

Innovation Solution

A protection circuit that includes a controller generating pulse width modulated signals to attenuate AC signals, with electrical isolation stages to isolate the controller from the switching and signal conditioning stages, allowing a single system controller to monitor multiple AC channels and reduce harmonic distortion using an electrically charged device for MOSFET gate voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If depletion MOSFET devices are used for AC bypass path, then AC current flow is provided, but system cost increases

Engineering Contradiction:

ImproveAC bypass path implementationVSAvoidsystem cost

Core Design Contradiction:

Ease of manufactureVSQuantity of substance

Solution Approach 1:

The patent combines enhancement mode MOSFET devices with a resistive element to create an equivalent depletion MOSFET bypass path. This merging of components achieves the same functional effect as depletion MOSFETs while using lower-cost enhancement mode devices and passive resistors, thereby reducing system cost while maintaining AC current flow capability.

Inventive Principle:

Principle #5Merging (Combining)

2Quantity of substance

If electromechanical relays are used for bypass path, then cost is reduced, but response time increases to 3-5 msec

Engineering Contradiction:

Improvesystem costVSAvoidresponse time

Core Design Contradiction:

Quantity of substanceVSSpeed

Solution Approach 1:

The patent replaces the electromechanical relay system with an electronic circuit consisting of enhancement mode MOSFET devices and a resistive element. This substitution eliminates the mechanical moving parts and magnetic field activation delays, achieving response times in the microsecond range rather than milliseconds, while maintaining cost-effectiveness through the use of standard enhancement mode MOSFETs instead of expensive depletion MOSFETs.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If multiple system controllers are used for multi-channel AC inputs, then each channel is monitored independently, but system complexity and communication requirements increase

Engineering Contradiction:

Improvechannel monitoring independenceVSAvoidsystem controller quantity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent designs a universal system controller architecture that can monitor and control multiple AC input channels through a single controller instance. The controller incorporates multiple AC input monitoring circuits and channel control logic, allowing one controller to perform the functions previously requiring multiple separate controllers. This reduces system complexity and inter-controller communication requirements while maintaining independent monitoring capability for each channel.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Ease of operation

If power supply is enabled before overage detection, then enhancement mode MOSFETs can be activated, but harmonic distortion increases on AC input line

Engineering Contradiction:

ImproveMOSFET activation capabilityVSAvoidharmonic distortion

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent implements a preliminary action sequence where the power supply is enabled and enhancement mode MOSFETs are activated in advance, before overage conditions are detected. The resistive element is pre-configured to provide the bypass path functionality. When overage conditions occur, the system can immediately modulate the MOSFETs to reduce AC power to the load. The preliminary activation eliminates delays in protection response while the controlled operation of MOSFETs and resistive element minimizes harmonic distortion generation.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9178352B2Performance and isolation improvements for digitally controlled AC attenuation and protection circuits

Publication Date: 2015.11.03 DOLBY LABORATORIES LICENSING CORP

AI summary

A protection and attenuation circuit for sensitive AC loads is described. The circuit provides AC power protection and attenuation utilizing high-efficiency switch-mode techniques to attenuate an AC power signal by incorporating a bidirectional, transistorized switch driven from a pulse width modulation signal, PWM. The circuit monitors characteristics of the AC power signal driving a known load and characteristics of the load or other elements and determines the duty cycle of the pulse width modulated signal, PWM, based upon the duration and amplitude of the over-voltage, over-current, over-limit or other event.