In-Rush Limiting Circuit Using Switchable Triac Bypass
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Solution Overview
Problem
In distributed building systems, power supplies experience a significant in-rush current surge during startup, which can overload circuit breakers and lead to erroneous interruptions, particularly when multiple power supplies are connected through a single circuit breaker.
Innovation Solution
A power supply circuit with an in-rush limiting arrangement that includes a current limiting resistive device, a triac, and an inductive winding, which limits the initial in-rush current by providing impedance until the triac bypasses the resistor, reducing the peak current draw and preventing circuit breaker overload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If power supplies are connected through a single circuit breaker, then power delivery to multiple devices is enabled, but in-rush current surge causes circuit breaker overload and erroneous interruptions
Solution Approach 1:
The circuit places a current limiting resistor in series with the power input before the power supply circuitry, establishing a current limiting arrangement before power is applied. This preliminary action ensures that when multiple power supplies are energized simultaneously, the resistor limits the in-rush current surge, preventing circuit breaker overload while still enabling power delivery to multiple devices.
2Reliability
If a current limiting resistor is placed in series with power input, then in-rush current is limited, but power loss increases due to resistive heating
Solution Approach 1:
The circuit employs a triac controlled by a microcontroller to dynamically switch the current limiting resistor out of the circuit. During startup, the triac remains off and the resistor limits in-rush current. Once the power supply reaches steady-state operation, the microcontroller activates the triac, which bypasses the resistor, thereby eliminating resistive power loss during normal operation while maintaining circuit breaker protection during startup.
Solution Approach 2:
The system uses its own power supply output to sense when steady-state operation is achieved and automatically controls the triac to bypass the current limiting resistor. This self-service mechanism eliminates the need for external control circuits or continuous monitoring, allowing the system to automatically optimize its own power consumption by removing the resistor from the circuit when it is no longer needed for protection.
3Ease of operation
If output capacitor is used to provide DC output supply voltage, then steady state operation is maintained, but in-rush current surge occurs during startup
Solution Approach 1:
The current limiting resistor is placed in the power input path before the output capacitor, establishing a current limiting arrangement before power is applied to the capacitor. This preliminary action prevents the capacitor from drawing excessive in-rush current during startup while still allowing it to charge to the required voltage for steady-state operation.
Solution Approach 2:
The triac acts as an intermediary component that can switch the current limiting resistor out of the circuit once the output capacitor is charged. During startup, the triac remains off and the resistor limits current to the capacitor. Once charging is complete, the microcontroller activates the triac, which bypasses the resistor and allows full power delivery to the capacitor without resistive loss.
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 the likelihood of circuit interruptions by managing the in-rush current, allowing the power supplies to transition to steady-state operation without overloading the circuit breakers, ensuring reliable power delivery to multiple devices.
Implementation Method 1
a second winding inductively coupled to the first inductive winding. The triac has a control input operably coupled to the second winding
Implementation Method 2
The current limiting resistive device is operably coupled between the second input terminal and circuit ground
Implementation Method 3
a capacitor coupled between the first output and circuit ground
Data Source
AI summary
An apparatus includes first and second input terminals, a conversion circuit, a current limiting resistive device, a triac and a second winding. The first and second input terminals are configured to be connected to a source of input power. The conversion circuit is operably connected to the first and second terminals, and includes a first inductive winding coupled between the first terminal and a switching device. The conversion circuit also includes a rectifier coupled between the first inductive winding and a first output, and a capacitor coupled between the first output and circuit ground.