Trailing-Edge Dimmer Circuit With dv/dt Feedback for Low EMI
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Solution Overview
Problem
Existing trailing edge phase control dimmer circuits generate excessive electromagnetic interference (EMI) emissions and suffer from high power dissipation due to prolonged turn-OFF transition times, which compromise their efficiency and maximum load capacity in controlling capacitive loads like LED drivers.
Innovation Solution
A trailing edge phase control dimmer circuit with a dv/dt feedback circuit that controls the turn-OFF transition profile by returning feedback current to the switching circuit, using an RC network to adjust the rate of change of the transition profile, thereby minimizing harmonics generation and power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the turn-OFF transition time of the switch is increased to produce a more gradual transition, then EMI emissions are minimized, but power dissipation increases and maximum load capacity decreases
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation (PWM) to switch the MOSFET on and off at high frequency. The switching transitions are confined to brief periodic intervals rather than being prolonged, which reduces the time during which power dissipation occurs while still achieving effective EMI control through synchronized switching at the end of each half-cycle
Solution Approach 2:
The patent employs dynamic control of the MOSFET switching transitions through dv/dt feedback. The feedback circuit dynamically adjusts the gate voltage to control the rate of change of drain voltage, enabling the transition to be completed quickly and efficiently. This dynamic control allows the transition to be both rapid (reducing power dissipation) and well-controlled (minimizing EMI)
2Object-generated harmful factors
If the turn-OFF transition time is increased to smooth the transition profile, then harmonics generation is reduced, but the transition time is extended causing additional power dissipation
Solution Approach 1:
The patent implements feedback control through the dv/dt feedback circuit that monitors the rate of change of drain voltage and adjusts the gate voltage accordingly. This feedback mechanism enables the transition to achieve a smooth profile (reducing harmonics) while completing the transition quickly (minimizing transition time and power dissipation). The feedback ensures that the transition is both rapid and well-controlled
Solution Approach 2:
The patent changes the parameter being controlled from the overall transition time to the rate of change of voltage (dv/dt). By controlling dv/dt rather than simply extending transition time, the patent achieves a smooth transition profile that minimizes harmonics while maintaining a rapid overall transition. This parameter change allows decoupling of transition smoothness from transition duration
3Object-affected harmful factors
If gradual switching OFF is implemented to reduce EMI, then EMI compliance is achieved, but switching losses increase reducing maximum load capacity
Solution Approach 1:
The patent replaces the mechanical/analog approach of gradually reducing switch conduction over an extended period with an electronic control mechanism using dv/dt feedback. This substitution enables the switching transition to be completed rapidly with controlled dv/dt, achieving EMI compliance through electronic control rather than prolonged gradual switching. The result is reduced switching losses and preserved maximum load capacity while maintaining EMI compliance
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
The solution effectively reduces EMI emissions and power dissipation by smoothing the turn-OFF transition profile without extending the transition time, enhancing the dimmer's efficiency and load capacity.
Implementation Method 1
a dv/dt feedback circuit for controlling a turn-OFF transition profile indicative of a drain voltage of the switching circuit of the turn-OFF transition and the selected turn-OFF transition time by returning at least some dv/dt feedback current generated by the switching circuit back to the switching circuit
Implementation Method 2
using an RC network to adjust the rate of change of the transition profile
Data Source
AI summary
A trailing edge phase control dimmer circuit for controlling alternating current (AC) power to a load, the circuit including: a switching circuit for controlling delivery of AC power to the load by conducting power to the load in an ON state and not conducting power to the load in an OFF state; and a switching control circuit for controlling turn-OFF and turn-ON of the switching circuit at each cycle of the AC to control switching of the ON and OFF states of the switching circuit, wherein the switching control circuit controlling turn-OFF of the switching circuit includes controlling a turn-OFF transition of the switching circuit between the ON state and the OFF state of the switching circuit extending for a selected turn-OFF transition time, and wherein the switching control circuit further includes a dv/dt feedback circuit for controlling a turn-OFF transition profile indicative of a drain voltage of the switching circuit of the turn-OFF transition and the selected turn-OFF transition time by returning at least some dv/dt feedback current generated by the switching circuit back to the switching circuit, whereby the dv/dt feedback circuit is configured to control said at least some dv/dt feedback current over the turn-OFF transition so as to reduce a rate of change of at least an initial region of the turn-OFF transition profile to minimize harmonics generation by the switching circuit.