Variable Load Circuit for Triac Dimmer Current Control
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Solution Overview
Problem
Conventional dimmer switches struggle to effectively control low wattage loads like LEDs due to insufficient current flow, leading to inefficient power dissipation when trying to maintain the triac's 'on' state, and existing solutions like adding a fixed resistor are wasteful.
Innovation Solution
A variable load circuit that adjusts its load characteristics during a half cycle of an alternating signal, allowing greater current flow during one portion and acting as a constant current sink during another, optimizing current flow to support triac-based dimmer switches while minimizing power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed resistor load is added in parallel with the low wattage load to maintain sufficient current flow through the dimmer switch, then the triac can properly truncate the hot signal and the dimmer control circuitry can charge, but the power dissipation increases and energy is wasted
Solution Approach 1:
The patent applies the dynamics principle by making the load resistance variable rather than fixed. The load circuit includes a switching element that dynamically changes the resistance value based on the instantaneous voltage of the alternating signal. During portions of the AC cycle when voltage is high, the switching element conducts to provide lower resistance and higher current. When voltage is low, the switching element non-conducts to provide higher resistance and lower current. This dynamic adjustment ensures sufficient current for triac operation only when necessary, eliminating continuous power waste.
Solution Approach 2:
The patent applies parameter changes by varying the electrical resistance parameter of the load circuit in response to changing voltage conditions. The switching element changes the circuit state between conducting and non-conducting, which fundamentally alters the resistance parameter. This parameter change allows the circuit to adapt to different voltage levels in the AC cycle, providing high current when voltage is high (to maintain triac holding current) and low current when voltage is low (to reduce power dissipation).
2Ease of operation
If the dimmer control circuitry charges during the truncated part of the dimmed hot signal half cycle, then the control function can be performed, but with low wattage loads the current flowing is not high enough to allow effective charging
Solution Approach 1:
The patent applies dynamics by making the load circuit dynamically responsive to voltage conditions. The switching element detects when voltage reaches levels sufficient for effective charging and activates accordingly. During portions of the AC cycle when voltage is high enough to enable effective charging of the dimmer control circuitry, the switching element conducts to provide the necessary current. This dynamic behavior ensures that charging current is available when voltage conditions permit, solving the problem of insufficient current for effective charging with low wattage loads.
3Reliability
If a variable load circuit allows greater current flow during one portion of the half cycle and acts as a constant current sink during another portion, then sufficient current is provided for charging and maintaining triac holding current, but the circuit complexity increases
Solution Approach 1:
The patent applies self-service by designing a load circuit that automatically adjusts its own resistance based on voltage conditions without external control. The switching element is connected in a configuration where it self-activates when voltage reaches certain levels and self-deactivates when voltage drops. The circuit uses the available voltage itself as the control signal, eliminating the need for separate control circuitry or external sensing components. This self-regulating behavior provides reliable current supply while minimizing circuit complexity.
Data Source
AI summary
A variable load circuit (2) is provided for use with a dimmer (1). A low wattage load such as a LED (3) is provided in series with the dimmer and the variable load circuit is provided in parallel with the LED. The variable load circuit has two different load characteristics: when the applied voltage from the dimmer is below a threshold, the variable load circuit presents a fixed load (24), and when the applied voltage is above a threshold the variable load circuit presents a variable load so as to act as a constant current sink. The variable load is provided by a secondary load portion (25) which may or may not act in combination with the fixed load (24), and the secondary load portion (25) is switched in or out of the variable load circuit by a trigger circuit portion (26).