Power Switch Device Inrush Current Control
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Solution Overview
Problem
Existing power switch devices for high-power load circuits, such as PWM inverter circuits, face issues with inrush current and voltage instability due to parasitic inductance and wiring resistance, leading to potential damage and instability in the power supply system, particularly when transitioning from open to closed states.
Innovation Solution
A power switch device utilizing a semiconductor switch, such as a bipolar transistor or MOSFET, with a protection MOSFET for reverse connection prevention, which gradually increases output voltage to control charging current to the ripple capacitor, eliminating the need for a precharge circuit and simplifying the start sequence, while maintaining high-speed starting and minimizing inrush current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a mechanical relay is used to close the power supply line, then the power switch device can transition from opening to closing, but large inrush current occurs due to rapid voltage rise, causing voltage drop and potential damage to the load circuit
Solution Approach 1:
The semiconductor switch is turned on before the relay contact closes to pre-charge the capacitor. This preliminary action reduces the voltage difference between the power source and capacitor at the moment of relay closure, thereby minimizing inrush current when the relay contact makes connection.
Solution Approach 2:
The semiconductor switch acts as an intermediary device between the power source and the capacitor. It provides a controlled current path during the transition period, allowing gradual charging of the capacitor before the relay contact closes, thus mediating the inrush current problem.
2Object-affected harmful factors
If a precharge circuit with resistors is added to reduce inrush current, then the charging operation can be controlled, but the circuit size and complexity increase
Solution Approach 1:
The semiconductor switch serves multiple functions: it acts as a precharge switch to control capacitor charging, functions as a power switch for the load circuit, and provides protection against reverse connection. By making the switch multi-functional, additional precharge circuitry is eliminated, maintaining circuit simplicity.
Solution Approach 2:
The control circuit automatically manages the semiconductor switch timing based on the operating state of the load circuit. The system self-regulates the precharge phase and power supply phase without requiring separate control mechanisms, eliminating the need for complex additional circuitry.
3Object-affected harmful factors
If the semiconductor switch is turned on before the load circuit operates, then the capacitor can be pre-charged, but inrush current may still occur if the switch is turned on too late
Solution Approach 1:
The control circuit monitors the operating state of the load circuit and uses this feedback information to determine the optimal timing for turning on the semiconductor switch. This feedback mechanism ensures the switch is activated at the precise moment needed for precharging, preventing both early activation (wasting time) and late activation (causing inrush current).
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 inrush current and stabilizes the power supply, allowing for high-speed starting without the need for additional circuitry, thereby minimizing circuit size and cost, and providing protection against reverse power source connections.
Implementation Method 1
the power supply line including a capacitor intended to stabilize the power supply voltage against fluctuations in the load current
Implementation Method 2
A power switch device utilizing a semiconductor switch, such as a bipolar transistor or MOSFET, with a protection MOSFET for reverse connection prevention
Data Source
Figure 1
Figure 2(a)~2
Figure 3
AI summary
A power switch device (100) provides and cuts off power supply to a load (14) in which a MOSFET (21) for causing a direct current power source (2) to be connected and disconnected is provided between power supply lines (12, 13) and the direct current power source (2), located upstream of the power supply lines (12, 13), the power supply lines (12, 13) including a ripple capacitor (15) for stabilizing the supply voltage against fluctuations in the load current in the load (14), powered by the direct current power source (2). The power switch device (100) is operated to transition power supply from closing to opening by gradually increasing the output voltage of the MOSFET (21) to minimize the value of current charging the ripple capacitor (15).