Backflow Prevention Circuit Using Level Shift Control
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Solution Overview
Problem
Conventional voltage regulators face issues with reverse current flow due to variations in process and temperature characteristics, which are not effectively addressed by existing methods that require controlling the threshold voltage to be lower than the forward voltage, increasing manufacturing costs.
Innovation Solution
A backflow prevention circuit and power supply circuit design that includes a p-channel MOS transistor and a backflow prevention control circuit, utilizing a level shift circuit and constant current source to switch the backflow prevention transistor from an on-state to an off-state when the output voltage exceeds the power supply voltage, thereby preventing reverse current flow without additional process control steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the threshold voltage VTH(inv) of the inverter circuit is controlled to be lower than the forward voltage Vf of the parasitic diode to prevent reverse current flow, then the reliability of backflow prevention is improved, but the manufacturing cost increases due to additional process control steps
Solution Approach 1:
The patent introduces a level shift circuit as an intermediary component between the inverter circuit and the backflow prevention transistor. This level shift circuit adjusts the voltage level to ensure that the backflow prevention transistor turns off when the output voltage exceeds the input voltage, without requiring direct control of the threshold voltage relationship between the inverter and parasitic diode. This mediator approach resolves the contradiction by achieving reliable backflow prevention through voltage level adjustment rather than strict threshold voltage control.
Solution Approach 2:
The patent changes the operating parameter from threshold voltage control to voltage level shifting. By using a level shift circuit to adjust the voltage level at the gate of the backflow prevention transistor, the system achieves reliable backflow prevention without needing to maintain a specific threshold voltage relationship. This parameter change eliminates the need for additional process control steps while maintaining prevention reliability.
2Device complexity
If a conventional inverter circuit is used to detect output voltage and control the backflow prevention transistor, then the device complexity is reduced, but the measurement precision of output voltage detection deteriorates due to threshold voltage variations with process and temperature
Solution Approach 1:
The level shift circuit serves as an intermediary that compensates for the imprecise threshold voltage detection of the conventional inverter circuit. By adjusting the voltage level at the gate of the backflow prevention transistor, the level shift circuit ensures accurate detection of the condition where output voltage exceeds input voltage, thereby improving measurement precision without increasing overall device complexity.
Solution Approach 2:
The patent changes the detection mechanism from direct threshold voltage comparison to voltage level shifting. The level shift circuit dynamically adjusts the reference voltage level based on the input voltage, allowing the inverter circuit to accurately detect when output voltage exceeds input voltage despite threshold voltage variations. This parameter change maintains simple circuit structure while improving detection precision.
Data Source
AI summary
Provided is a backflow prevention circuit including a backflow prevention transistor as a p-channel MOS transistor interposed in series between an input terminal to which a power supply voltage is supplied, and an output-stage transistor as a p-channel MOS transistor, configured to supply an output voltage from an output terminal, and a backflow prevention control circuit configured to turn off the backflow prevention transistor if the output voltage exceeds the power supply voltage. The backflow prevention control circuit includes a first transistor, a first current source circuit, and a level shift circuit.