Regulated Analog Switch for Automotive Load Protection
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Solution Overview
Problem
In high-voltage applications, existing MOSFET switches face challenges in protecting loads from excessive voltage while maintaining minimal drop voltage, especially when the battery voltage exceeds the threshold voltage, and ensuring the output voltage of integrated semiconductor circuits does not exceed the maximum allowable voltage, which is a concern in automotive applications where voltages can range from 12 to 40 Volts.
Innovation Solution
A regulated analog switch circuit is designed with a voltage divider, differential amplifying means, and resistive means to control the gate of a high-voltage transistor, ensuring the output voltage remains within a defined limit, and the ON-resistance is minimized by applying a maximal allowable gate-source voltage when the supply voltage is below the defined output voltage, using a two-stage Miller compensated amplifier for Miller compensation and current control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a simple MOSFET switch is used to pass analog signals, then the switch has low on resistance and high impedance when off, but the switch cannot protect the load from excessive voltage when battery voltage exceeds the maximum allowable voltage
Solution Approach 1:
A differential amplifier is introduced as an intermediary control element between the battery voltage source and the MOSFET gate. The amplifier monitors the output voltage and adjusts the gate voltage accordingly, acting as a mediator that enables voltage regulation without directly modifying the MOSFET structure. This resolves the contradiction by adding a control intermediary rather than complicating the switch itself.
Solution Approach 2:
The voltage regulation function is segmented from the switching function. The MOSFET handles the switching operation while the differential amplifier handles the voltage regulation. This segmentation allows each component to perform its specialized function optimally - the MOSFET provides low on-resistance switching while the amplifier provides precise voltage control to protect the load.
2Loss of energy
If the gate-source voltage is increased to minimize ON-resistance, then the switch conducts better with lower resistance, but the output voltage may exceed the maximum allowable voltage limit
Solution Approach 1:
A voltage feedback loop is implemented where the differential amplifier continuously monitors the output voltage and adjusts the MOSFET gate voltage in response. When output voltage approaches the maximum allowable limit, the amplifier reduces the gate voltage to maintain the limit, preventing excessive voltage while minimizing energy loss through optimal gate voltage control.
Solution Approach 2:
The gate voltage is made dynamic rather than fixed. The differential amplifier continuously adjusts the gate voltage based on the instantaneous output voltage conditions. This dynamic control allows the system to minimize ON-resistance (by applying sufficient gate voltage) while preventing output voltage from exceeding the maximum limit, resolving the contradiction between energy efficiency and voltage protection.
3Reliability
If a regulated analog switch circuit is added to control output voltage, then the output voltage remains within the defined limit, but the circuit complexity increases with additional components
Solution Approach 1:
The differential amplifier is configured to perform multiple functions: it monitors the output voltage, compares it with a reference voltage, and simultaneously controls the MOSFET gate voltage for both switching and regulation purposes. This multi-functionality achieves voltage regulation without requiring separate dedicated components for each function, thereby limiting the increase in circuit complexity.
Solution Approach 2:
The voltage regulation function is merged with the existing switching control structure. The differential amplifier integrates the voltage monitoring and MOSFET control into a unified circuit architecture. By merging these functions rather than adding completely separate regulation circuitry, the patent achieves output voltage regulation while minimizing the increase in overall circuit complexity.
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 ensures a constant output voltage within the defined limit, even with varying input voltages up to 40 Volts, and maintains minimal ON-resistance, preventing voltage exceeding the maximum allowable limit for integrated semiconductor circuits with minimal supply voltage loss.
Implementation Method 1
amplify the difference between the midpoint voltage of said voltage divider and said reference voltage and using the amplified difference to control the gate of said high-voltage transistor
Implementation Method 2
a voltage divider between said output voltage and ground
Implementation Method 3
a resistive means connected between said supply voltage and the gate of said transistor switch
Implementation Method 4
using a two-stage Miller compensated amplifier for Miller compensation and current control
Data Source
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AI summary
Circuits and methods to achieve a regulated analog switch being capable to provide an output-voltage not exceeding a defined limit are disclosed. In a preferred embodiment a car battery provides a supply voltage up to 40 Volts, wherein a load must not have an output voltage higher than 22 Volts. The drain-source ON-resistance of the switch, realized by a high-voltage MOSFET, is kept to a minimum. The voltage regulation of the preferred embodiment is performed by a single stage operational amplifier and a two-stage amplifier having Miller compensation.