Source-Follower Power Supply Clamp for Large Rush Voltage Response
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Solution Overview
Problem
Existing power supply circuits face challenges in effectively clamping output voltages during large rush voltage events, which can lead to excessive voltage application to downstream circuit units, compromising system stability and safety.
Innovation Solution
A power supply circuit design incorporating a first transistor with a source follower configuration, an amplifier circuit, and a capacitor to rapidly control the control signal and clamp the output voltage, along with an optional charge pump circuit for enhanced control, allowing for high-speed response to voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional power supply circuit is used, then the circuit structure is simple, but the response speed to large rush voltage is slow and cannot effectively clamp output voltage
Solution Approach 1:
The power supply circuit is segmented into multiple functional modules: a voltage generation unit with transistors Q1-Q4 and resistors R1-R4 for generating predetermined voltage, an amplification unit with operational amplifier OP1 for high-speed voltage comparison and amplification, and a control unit with transistor Q5 for clamping output voltage. This segmentation allows each module to perform its specific function efficiently, achieving fast response to rush voltage while maintaining clear functional separation.
Solution Approach 2:
The circuit implements feedback mechanisms where the operational amplifier OP1 continuously monitors the output voltage and compares it with a reference voltage, amplifying the voltage difference to generate control signals. Additionally, transistor Q5 provides feedback control by adjusting its conduction state based on the amplified signal to clamp the output voltage when rush voltage occurs, ensuring stable operation.
2Reliability
If the response speed is increased to clamp voltage quickly, then the clamping effectiveness improves, but the circuit complexity increases
Solution Approach 1:
The operational amplifier OP1 provides continuous feedback monitoring of the output voltage, comparing it with the predetermined voltage from the voltage generation unit. When the output voltage exceeds the predetermined level during rush voltage events, the amplifier generates a strong control signal that immediately activates transistor Q5 to clamp the output, ensuring reliable voltage protection while using feedback to minimize the number of additional components needed.
Solution Approach 2:
The circuit changes the operating parameters of transistor Q5 dynamically based on the voltage conditions. During normal operation, Q5 remains in a high-impedance state with minimal impact on the circuit. When rush voltage occurs and the amplified voltage difference exceeds a threshold, Q5 transitions to a low-impedance state to clamp the output voltage, providing effective protection without requiring complex control logic.
3Speed
If a fast response clamp circuit is implemented, then the voltage clamping becomes effective, but the phase margin of the amplifier circuit decreases
Solution Approach 1:
The circuit separates the voltage monitoring and clamping functions into distinct stages. The operational amplifier OP1 handles voltage comparison and signal amplification in the first stage, while transistor Q5 performs the actual voltage clamping in a second stage. This segmentation allows the amplifier to operate with adequate phase margin for stability while the clamping transistor provides the fast response needed for rush voltage protection, as the clamping action occurs after amplification rather than within the feedback loop.
Data Source
AI summary
A power supply circuit in an embodiment includes a first transistor controlled to be turned on and off by a control signal supplied to a gate to output an output voltage following a predetermined voltage, a second transistor, one end of a current path of which is connected to an input terminal for supplying a power supply voltage, the second transistor outputting the predetermined voltage according to the control signal, and an amplifier circuit configured to amplify a voltage difference between a reference voltage and the predetermined voltage, and output the voltage difference as the control signal.