Power-Down Discharger Circuit for Capacitor Discharge
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Solution Overview
Problem
Integrated circuits, such as power switches and voltage regulators, face issues with residual charges in capacitors that lead to undesired behavior upon power restoration, particularly inrush currents due to incomplete discharge of external capacitors.
Innovation Solution
The implementation of a power-down discharger circuit that actively drives a discharge transistor to a conducting state after a power supply voltage drop, utilizing an internal or external capacitance to store energy for discharging capacitors and MOSFET gates, ensuring complete discharge before power recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If depletion-mode MOSFETs are used to discharge capacitors after power loss, then capacitor discharge reliability is improved, but device complexity and manufacturing compatibility worsen
Solution Approach 1:
The patent replaces expensive depletion-mode MOSFETs with standard enhancement-mode MOSFETs combined with a simple discharge transistor and capacitor network. The discharge transistor is temporarily activated after power loss to force capacitor discharge, then deactivated. This disposable-like approach uses inexpensive, easily manufactured components that perform the discharge function only when needed, eliminating the need for complex depletion-mode devices while maintaining reliability.
2Speed
If the discharge transistor is actively driven after power loss, then capacitor discharge speed is improved, but energy consumption worsens
Solution Approach 1:
The discharge transistor is activated periodically or transiently only after power loss detection, rather than continuously. The circuit monitors power supply status and triggers the discharge transistor briefly to force capacitor discharge, then deactivates it. This periodic activation achieves fast discharge when needed while consuming minimal energy during normal operation, resolving the contradiction between discharge speed and energy consumption.
3Reliability
If the internal capacitance is used to store energy for driving the discharge transistor, then discharge capability after power loss is improved, but the risk of energy drainage before discharge completion worsens
Solution Approach 1:
The patent introduces a diode as an intermediary component between the internal capacitance and the discharge transistor. The diode acts as a one-way valve that allows the internal capacitance to charge during normal operation but prevents it from discharging unintentionally before the power loss event. When power is lost, the diode becomes forward-biased, allowing the stored energy to flow to the discharge transistor and force capacitor discharge. This intermediary protects against premature energy drainage while ensuring reliable discharge capability when needed.
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
This solution ensures proper startup behavior and prevents inrush currents by ensuring capacitors are fully discharged before power restoration, effectively addressing the residual charge issue in integrated circuits.
Implementation Method 1
The power-down discharger may include, or be coupled to, an internal capacitance that is charged when the power supply voltage is above the threshold, thereby storing sufficient energy for driving the discharge transistor after the power supply voltage drops below the threshold
Implementation Method 2
A diode is employed to ensure that the loss of power does not drain away the needed energy until after the discharge has been completed
Data Source
AI summary
Active post-power loss discharging of capacitors is provided. In an integrated circuit having a startup behavior depending on a capacitor voltage, a discharge transistor is provided to discharge the capacitor. A power-down discharger actively drives the discharge transistor after a power supply voltage drops below a threshold. The power-down discharger may include, or be coupled to, an internal capacitance that is charged when the power supply voltage is above the threshold, thereby storing sufficient energy for later driving of the discharge transistor. A diode is employed to ensure that the loss of power does not drain away the needed energy until after the discharge has been completed. One illustrative discharging method includes: sensing a condition indicative of power supply voltage loss for an integrated circuit; and actively driving the discharge transistor into a conducting state. The sensing may include driving the discharge transistor inversely to a signal from a pin.