Cascode Voltage Regulator With Current Limiting for High Input Voltage
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Solution Overview
Problem
Existing voltage regulator circuits face limitations in high voltage applications due to the maximum allowable input voltage limit set by the maximum drain to source voltage of transistors, restricting circuit configurations and design possibilities.
Innovation Solution
A cascode voltage regulator circuit is developed using drain-extended transistors, which allows for higher input voltages by configuring a cascode source follower with current limiting capabilities and a reference generator circuit providing offset bias voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional voltage regulator circuits are used, then the circuit is simple to design, but the maximum input voltage is limited by the transistor's drain to source voltage rating
Solution Approach 1:
The voltage regulator circuit is divided into multiple transistor stages (first transistor for voltage regulation, second transistor for current limiting) connected in a cascode configuration. This segmentation allows each transistor to handle a portion of the total voltage, enabling the circuit to regulate voltages higher than any single transistor's rating while maintaining manageable complexity through modular design.
Solution Approach 2:
The circuit employs a nested structure where the second transistor is positioned within the voltage regulation path of the first transistor. The cascode configuration nests the current-limiting function inside the voltage-regulation function, allowing compact integration of multiple protection mechanisms without proportionally increasing circuit complexity.
2Adaptability or versatility
If higher input voltages are accommodated, then the circuit can handle more applications, but the transistor voltage rating must be increased
Solution Approach 1:
Instead of requiring a single high-voltage transistor, the circuit segments the voltage handling across multiple standard-rated transistors. The first transistor handles the regulated voltage portion while the second transistor handles the excess voltage, allowing the use of readily available transistors with standard voltage ratings to achieve high-voltage operation.
Solution Approach 2:
The second transistor acts as an intermediary protective element between the high-voltage input and the first regulation transistor. It limits the voltage stress on the first transistor by clamping the voltage differential, thereby protecting the main regulation element while enabling operation at higher input voltages.
3Reliability
If current limiting is added to protect the circuit, then the reliability improves, but the circuit complexity increases
Solution Approach 1:
The current limiting function is merged with the voltage regulation function by using the second transistor in a cascode configuration with the first transistor. This combining of functions allows current limiting protection to be implemented without adding separate protection circuits, thereby improving reliability while minimizing the increase in overall circuit complexity.
Solution Approach 2:
The second transistor serves multiple functions simultaneously: it acts as a current limiter to protect against overload, provides voltage division to protect the first transistor, and maintains the regulation function through its cascode connection. This multi-functionality improves circuit protection while avoiding the need for additional dedicated protection components.
Data Source
AI summary
An example cascode voltage regulator circuit includes a first transistor coupled to an input voltage terminal and configured as a source follower to provide an output voltage at a source terminal, a second transistor coupled in series between the source terminal of the first transistor and an output terminal, the second transistor configured as a current limiter, and a current mirror coupled between respective first and second control terminals of the first and second transistors, the current mirror configured to receive a first current indicative of a source follower current flowing through the first transistor and to turn off the second transistor by coupling the first and second control terminals together responsive to the source follower current exceeding a threshold. In an example, the first transistor is a drain-extended NMOS device and the second transistor is a drain-extended PMOS device.