Active Pre-Charge Circuit With Duty-Cycle Inrush Current Control
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Solution Overview
Problem
Industrial power supplies face challenges in managing large inrush currents during the power-up stage of charge storage devices, which can damage the power supplies and require oversized, expensive components to handle these spikes.
Innovation Solution
An active pre-charge circuit using a switching transistor controlled by a current controller to regulate current flow, eliminating the need for large power resistors and relays, and incorporating a buck converter configuration with a recirculating diode to manage inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a proper pre-charge circuit is used to charge storage devices at lower current during power-up, then the power supply size and cost are reduced, but the circuit complexity increases due to additional components needed to control inrush current
Solution Approach 1:
The patent employs a dynamic switching mechanism using a transistor controlled by a controller to adjust the pre-charge current in real-time. The controller receives current measurements and dynamically adjusts the switching duty cycle to maintain current within a desired range, transforming a static circuit into a dynamically adaptive system that optimizes both power supply size and current control.
Solution Approach 2:
The patent implements a feedback control loop where a sensor measures the pre-charge current and provides this information to the controller. The controller processes this feedback and adjusts the transistor switching duty cycle accordingly, creating a closed-loop system that automatically maintains current within desired limits while preventing inrush spikes.
2Reliability
If all power supplies are configured to supply start-up power at any time, then the machine can start reliably, but the power supply becomes much larger and more expensive
Solution Approach 1:
The patent applies preliminary action by pre-charging the storage device before the main power supply needs to deliver full start-up power. The pre-charge circuit operates during a preliminary phase to charge capacitors to a desired voltage level, so when the main power supply activates, the storage device is already prepared and the inrush current is limited, allowing the power supply to be sized for normal operation rather than peak start-up demands.
Solution Approach 2:
The patent uses periodic switching action through the transistor, which switches on and off at controlled intervals during the pre-charge phase. This periodic action allows current to flow in controlled pulses rather than continuous DC, enabling the power supply to be smaller while still achieving reliable start-up through the cumulative effect of periodic charging.
3Ease of manufacture
If charge storage devices are connected directly to the power supply during pre-charge phase, then the charging process is simple, but large inrush current may damage the power supply
Solution Approach 1:
The patent introduces a transistor as an intermediary component between the power supply and the charge storage device. This intermediary element acts as a controlled valve that regulates current flow, preventing direct connection inrush current while still allowing efficient charging. The transistor, controlled by the controller based on current feedback, mediates the energy transfer to eliminate harmful inrush effects.
Solution Approach 2:
The patent replaces traditional mechanical current limiting methods (such as series resistors or relay-based switching) with an electronic control system using a transistor and controller. This substitution eliminates the need for large power resistors, relays, and heat sinks while providing more precise and adaptive current control, reducing both circuit complexity and component size.
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 controls pre-charge currents below desired levels, reducing the risk of component damage and enabling smaller, more efficient power supplies by eliminating the need for bulky and costly components.
Implementation Method 1
a transistor configured to control current pre-charging a charge storage device
Implementation Method 2
a diode having an anode coupled with a source of the transistor, and a cathode coupled with a drain of the transistor
Implementation Method 3
an inductor coupled between the shunt resistor and the positive end of the charge storage device
Implementation Method 4
a shunt resistor coupled between the source of the transistor and a positive end of the charge storage device
Data Source
AI summary
A circuit includes a transistor configured to control pre-charging a charge storage device, and a diode coupled in parallel with the transistor. It also includes a shunt resistor coupled between the source of the transistor and a positive end of the charge storage device, an inductor coupled between the shunt resistor and the positive end of the charge storage device, and a current controller coupled to a gate of the transistor. The current controller is configured to receive a current measurement indicating an amount of current flowing through the transistor, process the current measurement to determine a switching duty cycle for the transistor, and to provide a signal to the gate of the transistor, the signal oscillating at the switching duty cycle. It also includes a power supply coupled with the source of the transistor and the drain of the transistor and configured to supply power to the current controller.