Dual N-Channel FET Power Feed Control for Reverse Battery Protection
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Solution Overview
Problem
Existing power feeding control devices for vehicles risk improper operation when the DC power supply is connected in reverse, as the voltage of the DC power supply can be applied to the gates of the FETs via the switching circuit, leading to unintended current flow.
Innovation Solution
A power feeding control device is designed with a first N-channel FET and a second N-channel FET, along with a diode and a switching circuit. The parasitic diode in each FET is connected such that the cathode and anode are connected to the drain and source, respectively. The switching circuit adjusts the gate voltage of the FETs with respect to the potential of the diode's anode, preventing the DC power supply voltage from being applied to the FET gates during reverse connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the switching circuit adjusts the gate voltage of FETs with respect to the second terminal potential, then the FETs can be switched ON or OFF effectively, but the voltage of the DC power supply may be applied to the gates of the FETs via the switching circuit when the DC power supply is in reverse connection
Solution Approach 1:
The patent introduces a diode as an intermediary component between the switching circuit and the FET gates. This diode acts as a protective barrier that prevents reverse voltage from reaching the FET gates while allowing normal operation. The diode's anode is connected to the switching circuit output and its cathode is connected to the FET gates, creating a unidirectional protection mechanism.
Solution Approach 2:
The patent applies preliminary protective action by configuring the diode orientation before reverse connection can occur. The diode is pre-configured with its cathode facing the FET gates, so that when reverse voltage is applied to the power supply terminals, the diode becomes reverse-biased and blocks the harmful voltage from reaching the FET gates before damage can occur.
2Productivity
If two N-channel FETs are arranged in a current path with parasitic diodes, then current flow can be controlled, but the parasitic diodes may conduct current during reverse connection if the FETs are not properly protected
Solution Approach 1:
The diode introduced in the patent serves as an intermediary protective element that prevents harmful reverse voltage from affecting the FET gates and parasitic diodes. By placing this protective diode in the gate control circuit, the patent ensures that the FETs remain properly controlled and their parasitic diodes do not conduct unintended current during reverse connection scenarios.
Solution Approach 2:
The patent converts the potentially harmful reverse voltage into a beneficial protective mechanism. When reverse connection occurs, the protective diode becomes reverse-biased and blocks the reverse voltage, effectively using the reverse voltage condition itself to activate the protection mechanism. This transforms what would be a harmful situation into a safe state where the FETs and load are protected from damage.
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 effectively prevents the voltage of the DC power supply from being applied to the gates of the FETs during reverse connection, thereby ensuring that the load does not operate improperly due to unintended current flow.
Implementation Method 1
In each of the two FETs, a parasitic diode is formed in which the cathode and the anode are connected to the drain and the source, respectively
Implementation Method 2
The value of the resistance between the drain and the source is adjusted by adjusting the gate voltage at the two FETs. The two FETs are switched ON by adjusting the value of resistance at the two FETs to sufficiently large value. The two FETs are switched OFF by adjusting the value of resistance of the two FETs to sufficiently small values.
Data Source
AI summary
In a power feeding control device, N-channel first FET and second FET are located in a current path for current flowing from a positive terminal to a negative terminal. The drain of the first FET is located downstream of the source. The drain of the second FET is located upstream of the source. The cathode of a first diode is connected to the negative terminal. A first drive circuit and a second drive circuit switch ON or OFF the first FET and the second FET by adjusting the gates of the first FET and the second FET, with respect to the cathode of the first diode.