Shunt Regulator with Startup Circuit for Overvoltage Protection
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Solution Overview
Problem
Circuits are vulnerable to electrical overstress from overvoltage or overcurrent conditions, such as electrostatic discharge and voltage spikes, which can cause damage and reliability issues in devices like USB connectors and portable devices.
Innovation Solution
A current shunting circuit comprising a low voltage supply circuit, current limit circuit, startup circuit, and shunt circuit, which includes a switch and control circuit to regulate voltage and shunt excess current to a reference terminal, maintaining a constant voltage level and preventing damage from voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shunt circuit is used to protect against overvoltage conditions, then circuit reliability is improved, but the circuit becomes vulnerable to startup failures when supply voltage is below minimum operating voltage
Solution Approach 1:
The patent introduces a startup circuit as an intermediary component between the supply voltage source and the shunt regulator. This startup circuit includes a startup capacitor and startup transistor that temporarily store and release energy during the startup phase, enabling the shunt regulator to initialize properly even when the supply voltage is initially below the minimum operating voltage. The startup circuit acts as a mediator that bridges the gap between insufficient initial voltage and the voltage requirements of the main circuit.
2Stability of the object's composition
If the shunt regulator continuously shunts current to maintain constant voltage, then voltage regulation is improved, but power consumption increases during normal operation
Solution Approach 1:
The patent implements dynamic control of the shunt regulator by using a control transistor (PMOS transistor 235) whose gate voltage is dynamically adjusted based on the difference between the internal voltage rail and reference voltage. The regulator transitions between different operating states: actively shunting current when voltage exceeds the reference, reducing current when voltage is close to reference, and stopping current flow when voltage is below reference. This dynamic operation maintains voltage stability while minimizing unnecessary power consumption during normal operating conditions.
3Reliability
If the shunt circuit switches to low ohmic state to shunt current, then protection against electrical overstress is improved, but excessive current flow can still occur during transient conditions
Solution Approach 1:
The patent implements preliminary current limiting through current limit resistors (222, 224, 226) that are positioned in series with the shunt transistor before it can switch to the low ohmic state. These resistors pre-limit the maximum current that can flow through the shunt transistor, preventing excessive current surges during transient conditions such as voltage spikes or hot-plug events. The current limit resistors ensure that even when the shunt transistor fully conducts, the current remains within safe bounds, thereby protecting the circuit while still providing effective overstress protection.
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 effectively regulates voltage and limits current to prevent damage from electrical overstress, ensuring reliable operation of low voltage devices even under high supply voltage conditions, such as those encountered in USB, HDMI, and car charger applications.
Implementation Method 1
A capacitor is connected across the gate of the shunting circuit and ground/common terminal. The capacitor operates to maintain the voltage at the gate at an about steady value in response to voltage fluctuations on the bandgap voltage supply line
Implementation Method 2
The shunting circuit is responsive to the voltage at the gate and an increase in voltage on the bandgap voltage supply line by passing increased current between the bandgap voltage supply and the ground circuit and regulating the bandgap voltage supply to the bandgap reference voltage circuit at an about constant level
Implementation Method 3
A bandgap reference voltage circuit is coupled to a bandgap voltage supply line and configured and arranged to provide a bandgap reference voltage output
Data Source
AI summary
Low voltage circuits are protected from high voltage/current conditions, as may be implemented in accordance with one or more example embodiments. An additional/secondary shunt circuit/switch is implemented to shunt additional current as supply voltage steps or otherwise increases. In some implementations, the secondary shunt circuit includes a transistor having its drain coupled to its gate via a large capacitance that operates to maintain the gate voltage at about a constant level. This operates to facilitate the draining of additional current, and maintaining a low bandgap voltage supply level.