JFET Charging Device Gate Voltage Control
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Solution Overview
Problem
The junction field-effect transistor (JFET) in charging chips experiences a decrease in output current as load voltage increases, limiting the charging speed and preventing the target load from reaching the desired voltage level due to pinch-off voltage limitations.
Innovation Solution
A charging device with a control circuit that adjusts the control voltage on the gate of the JFET, shifting the charging current-voltage curve to the right, maintaining a charging current output as the load voltage approaches the pinch-off voltage, and includes an output current control circuit to prevent excessive current intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a JFET is used in the charging chip, then the charging device has simple structure and low cost, but the output current decreases as load voltage increases, limiting charging speed and preventing the target load from reaching desired voltage level
Solution Approach 1:
The patent applies dynamics by making the gate voltage adjustable rather than fixed. The control circuit dynamically adjusts the gate voltage of the JFET based on the charging state, allowing the device to adapt its characteristics during operation. This enables the JFET to maintain effective output current over a wider voltage range, solving the contradiction between simple structure and charging speed.
Solution Approach 2:
The patent changes the electrical parameters of the JFET by adjusting the gate voltage. By varying the gate voltage through the control circuit, the pinch-off voltage and output characteristics of the JFET are modified dynamically. This allows the charging device to maintain high charging speed without requiring a completely different device structure.
2Ease of operation
If the JFET operates at constant gate voltage, then the device operation is simple, but when load voltage reaches pinch-off voltage, the output current decreases to zero, unable to continue charging
Solution Approach 1:
The patent implements feedback by having the control circuit monitor the charging state and adjust the gate voltage accordingly. The control circuit receives feedback about the load voltage and output current, then modifies the gate voltage to prevent the JFET from reaching the pinch-off state where current would drop to zero. This ensures reliable charging completion while maintaining simple operation.
Solution Approach 2:
The control circuit performs preliminary action by adjusting the gate voltage before the JFET reaches the pinch-off voltage. By proactively modifying the gate voltage in anticipation of the pinch-off condition, the system prevents current dropout and ensures continuous charging capability throughout the entire charging process.
3Productivity
If the output current is increased to improve charging speed, then the charging speed increases, but excessive current intensity may cause overheating or short-circuiting
Solution Approach 1:
The patent uses dynamics to adjust the output current based on real-time charging conditions. The control circuit dynamically modulates the gate voltage to optimize the output current, allowing high current when needed for fast charging while automatically reducing current when approaching safety limits. This resolves the contradiction between charging speed and safety by making current intensity adaptive rather than fixed.
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 enhances the charging speed of the target load by maintaining output current near pinch-off voltage, ensuring the target load is charged to the desired voltage level while protecting against overheating or short-circuiting.
Implementation Method 1
a junction field-effect transistor (JFET), comprising at least: a drain, electrically connected to the input terminal so as to receive the input voltage; a source, electrically connected to the output terminal so as to output an output voltage and an output current; and a gate, electrically connected to the control terminal
Data Source
AI summary
The disclosure provides a charging device, which includes an input terminal configured to receive an input voltage; an output terminal configured to connect a target load so as to charge the target load; a control terminal, configured to receive a control voltage; a junction field-effect transistor and a control circuit. The junction field-effect transistor includes at least: a drain, electrically connected to the input terminal so as to receive the input voltage; a source, electrically connected to the output terminal so as to output an output voltage and an output current; and a gate, electrically connected to the control terminal. The control circuit is electrically connected to the control terminal, and configured to change the control voltage based on a change in a load voltage so as to change a pinch-off voltage of the JFET by controlling a bias voltage on the gate, thereby controlling the output current.