Linear Power Source Depletion NMOSFET Startup Boost
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Solution Overview
Problem
Linear power sources face a trade-off between reducing power consumption and minimizing startup time, as decreasing the driving current at the output stage prolongs the startup time.
Innovation Solution
Incorporating a depletion type NMOSFET that generates a drain current which decreases as the output voltage rises, adding this current to the driving current at startup, and configuring it to continue or cease based on a constant voltage threshold, allowing for efficient current boosting during startup without increasing power consumption during normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the driving current at the output stage is reduced to decrease power consumption, then power consumption is reduced, but startup time is prolonged
Solution Approach 1:
The patent applies dynamics by making the driving current variable rather than constant. A capacitor is connected to the gate of the output transistor to provide a temporary current boost during startup, then the current automatically reduces to a low level during normal operation. This dynamic current adjustment resolves the contradiction between low power consumption and fast startup time.
Solution Approach 2:
The patent uses preliminary action by pre-charging the capacitor connected to the output transistor gate before the output stage activates. This preliminary charge provides immediate high current during startup to quickly charge output capacitors, then the capacitor discharges to maintain gate voltage while consuming minimal current during normal operation.
2Loss of time
If the driving current is increased to reduce startup time, then startup time is reduced, but power consumption increases
Solution Approach 1:
The patent implements periodic action through the capacitor's charge-discharge cycle. During startup, the capacitor is charged to provide high current (charging phase). During normal operation, the capacitor maintains the gate voltage with minimal current leakage (discharge/maintenance phase). This periodic high-current-then-low-current pattern achieves fast startup without sustained high power consumption.
Solution Approach 2:
The dynamic behavior of the capacitor allows the system to automatically transition from high current mode during startup to low current mode during normal operation, resolving the contradiction between startup speed and power consumption.
Data Source
AI summary
A linear power source includes: an output transistor connected between an input terminal of an input voltage and an output terminal of an output voltage; a driver configured to drive the output transistor so that the output voltage or a feedback voltage corresponding to the output voltage matches a predetermined reference voltage; and a depletion type NMOSFET configured to generate a drain current that decreases as the output voltage rises, and to add the drain current to a current to be boosted at startup.