Capacitive Power Supply Surge Current Limitation
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Solution Overview
Problem
Conventional power supply circuits with surge current limiting elements experience permanent dissipation in steady state, reducing system efficiency due to the continuous operation of these elements beyond the initial voltage settling phase.
Innovation Solution
Incorporating a triac in parallel with the surge current limiting resistor, controlled by a diac setting a threshold voltage, to short-circuit the resistor in steady state, thereby reducing dissipation and using additional capacitive elements to provide a power supply voltage for the triac's gate current, allowing it to turn on only when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surge current limiting element (resistor) is provided in the power supply circuit, then surge current is limited during power-on, but permanent dissipation occurs in steady state reducing system efficiency
Solution Approach 1:
The patent applies the dynamics principle by making the resistor's state changeable through a triac switch. The resistor is dynamically connected or disconnected based on operating conditions: connected during power-on to limit surge current, and disconnected in steady state to eliminate permanent dissipation. This transforms a static resistor into a dynamically controllable element that adapts its presence in the circuit.
Solution Approach 2:
The patent implements periodic action through the triac switch that periodically connects and disconnects the resistor based on the AC power cycle and voltage threshold detection. The diac-triggered triac creates periodic switching action, connecting the resistor only when needed (during surge conditions) and disconnecting it during normal operation, thereby achieving energy efficiency while maintaining surge protection capability.
2Loss of energy
If a triac is added to control the resistor, then dissipation is reduced in steady state, but device complexity increases
Solution Approach 1:
The patent applies self-service through the voltage-dependent triggering mechanism. The circuit automatically detects when the capacitor voltage reaches the threshold set by the diac and autonomously triggers the triac to disconnect the resistor. No external control signal or complex control circuitry is needed - the circuit serves itself by using its own operating voltage to control the switching action, thereby minimizing added complexity.
Solution Approach 2:
The patent uses the diac as an intermediary element between the capacitor voltage and the triac gate. The diac acts as a voltage threshold mediator that converts the continuous capacitor voltage into a discrete triggering signal for the triac. This simple intermediary component enables automatic control without requiring complex control circuits, microcontrollers, or additional sensing elements.
3Loss of energy
If the triac is used to short-circuit the resistor, then surge current dissipation is minimized, but additional capacitive elements are required for gate current
Solution Approach 1:
The patent applies multi-functionality by making the main series capacitor serve dual purposes: it limits surge current during power-on and simultaneously provides the gate current for the triac through voltage division with the diac. This eliminates the need for separate gate current sourcing circuitry or additional capacitive elements dedicated solely to triac operation, thereby reducing overall component count despite adding the triac and diac.
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 configuration limits surge current dissipation in the power supply circuit, improving efficiency by minimizing unnecessary energy loss during steady-state operation.
Implementation Method 1
a bidirectional switch in parallel on the resistor... a control electrode of the triac is grounded via an element setting a threshold voltage
Implementation Method 2
the power supply further comprises a third capacitive element between a power terminal of the triac on the D.C. voltage side and the ground
Data Source
AI summary
A capacitive power supply including: a first capacitive element and a first resistive element in series between a first terminal of a power switch and at least one rectifying element having a second terminal connected to a first electrode of at least one second capacitive element for providing a D.C. voltage; and a bidirectional switch in parallel on the resistor.