Single-FET Dimmer Circuit With Body-Diode Blocking

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Solution Overview

Problem

Conventional dimmers using MOSFETs face the challenge of current flow due to the body diode, which requires redundant FETs to prevent current flow, increasing manufacturing costs.

Innovation Solution

A dimmer device with temperature compensation that utilizes a single FET connected in a full-wave bridge rectifier configuration, where the body diode is reverse-biased during each half cycle, and a thermally sensitive component to adjust the FET's on-time based on temperature and user-adjustable load settings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If two FETs are used in series to block current flow, then current blocking capability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvecurrent blocking capabilityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

A body diode is introduced as an intermediary element within the single FET structure. The body diode is reverse-biased during normal operation to block current flow in the reverse direction, eliminating the need for a second FET while maintaining reliable current blocking capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent combines the current blocking function with the existing FET structure by utilizing the body diode inherent to the FET device. This merging of functions allows a single FET to perform both switching and current blocking roles that previously required two separate FETs.

Inventive Principle:

Principle #5Merging (Combining)

2Device complexity

If a single FET is used to control power, then device complexity is reduced, but current leakage through body diode increases

Engineering Contradiction:

Improvedevice complexityVSAvoidcurrent leakage

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent employs periodic gating signals to control the FET switching operation. By applying gate voltage only during specific portions of the AC cycle when needed, the FET is turned on only periodically to deliver power to the load, while the reverse-biased body diode blocks current during other periods.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes the electrical parameters (gate voltage) of the FET to control its operation. By adjusting the gate voltage, the FET can be turned on or off to control power delivery, and the body diode's reverse bias is maintained through proper circuit configuration to prevent current leakage.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If FETs are used without temperature compensation, then device simplicity is maintained, but thermal runout risk increases

Engineering Contradiction:

Improvedevice simplicityVSAvoidthermal stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent implements a temperature sensing circuit that continuously monitors the temperature of the FET and provides feedback to the control circuit. When the FET temperature exceeds a predetermined threshold, the control circuit reduces or shuts off power delivery to prevent thermal runout, maintaining reliable operation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent incorporates preventive measures by monitoring FET temperature before thermal runout occurs. The temperature sensing and control circuitry detects temperature increases in advance and takes corrective action (reducing power delivery) to prevent the FET from reaching dangerous temperature levels.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 solution effectively blocks current flow through the body diode except when a sufficient gate voltage is applied, reducing manufacturing costs by eliminating the need for redundant FETs and providing efficient temperature compensation to prevent overheating.

Implementation Method 1

a thermally sensitive component disposed such that an electrical characteristic of the thermally sensitive component is representative of a temperature of the bridge rectifier

Methodology Applied

Scientific EffectThermal sensitivity: Thermistor

Implementation Method 2

the field-effect transistor being connected between the first output terminal and the second output terminal such that the body diode blocks current between the first output terminal and the second output terminal

Methodology Applied

Scientific EffectBody diode blocking: Diode

Implementation Method 3

wherein the controller is configured to apply a voltage to the gate of the field-effect transistor such that the field-effect transistor is on for an on-time occurring during at least a portion of each half cycle of the mains input

Methodology Applied

Scientific EffectField-effect transistor conduction:

Data Source

PatentUS20250142695A1Electrical Wiring Device for Providing Variable Power

Publication Date: 2025.05.01 PASS & SEYMOUR INC

AI summary

A power control device for providing variable power to a load. The power control device including a single FET employed in conjunction with a bridge rectifier to reverse bias the body diode of the FET except for when a sufficient voltage is provided to the gate of the FET. A temperature compensation circuit reduces the on-time of the bridge rectifier when a thermally sensitive component indicates that the temperature of the bridge rectifier has exceeded a threshold.