Active Capacitor Discharge Circuit for Low Idle Loss and Fast Discharge
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Solution Overview
Problem
Existing switching power supplies with large capacitors face inefficiencies in discharging stored energy when de-powered, leading to unnecessary power consumption and inefficient discharge time due to the use of resistors and bleed resistors, and lack of a simple discharge mechanism for the bulk capacitor may not be optimal.
Innovation Solution
An active capacitor discharge circuit that includes a current source and a voltage-controlled switch that includes a current source and a voltage-controlled switch that selectively opens and closes to reduce power consumption and a voltage-controlled switch that selectively opens and closes to reduce power consumption and discharge capacitors efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If resistors and bleed resistors are used to discharge capacitors, then the discharge function is provided, but power consumption increases and discharge time becomes inefficient
Solution Approach 1:
The patent uses a depletion mode MOSFET that can dynamically adjust its channel conductivity based on gate voltage, transitioning from a high-conductivity state during discharge to a high-impedance state during normal operation. This dynamic switching capability allows the system to achieve fast discharge when needed while minimizing continuous power consumption, resolving the contradiction between discharge speed and power loss.
Solution Approach 2:
The invention changes the electrical parameters of the discharge path by using a voltage-controlled MOSFET that can alter its on-resistance from very low (enabling fast discharge) to very high (minimizing power loss). By controlling the gate voltage, the system can switch between these parameter states to optimize both discharge time and power consumption at different operational phases.
2Reliability
If a discharge mechanism is always connected to capacitors, then discharge function is available, but continuous power is consumed
Solution Approach 1:
The patent implements periodic discharge action by using the depletion mode MOSFET to enable discharge only when required (such as during power-down or fault conditions) rather than maintaining continuous discharge connectivity. The MOSFET switches between conducting and blocking states, creating periodic rather than continuous power consumption while ensuring discharge functionality is available when needed.
Solution Approach 2:
The invention extracts the discharge function from a continuously connected circuit and places it behind a voltage-controlled switch. This allows the discharge path to be isolated from the main circuit during normal operation, eliminating continuous power consumption, while maintaining the capability to activate the discharge function when required for safety or operational reasons.
3Device complexity
If simple discharge mechanisms are used, then device complexity is reduced, but discharge efficiency and power management are insufficient
Solution Approach 1:
The depletion mode MOSFET is configured to be self-controlled through its inherent characteristics, where the gate voltage naturally develops from the capacitor voltage itself during discharge. This self-service mechanism eliminates the need for external control circuits or additional components, achieving high discharge efficiency while maintaining simple circuit topology. The MOSFET automatically regulates its own operation based on the capacitor's voltage state.
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 active capacitor discharge circuit reduces power loss and discharge time by using a depletion mode MOSFET and a P-channel JFET, which are capable of providing a current source and a voltage-controlled switch that selectively opens and closes to reduce power consumption and discharge capacitors efficiently.
Implementation Method 1
the current source comprises a depletion mode MOSFET coupled to a source resistance such that a channel of the depletion mode MOSFET is in series with the source resistance
Implementation Method 2
the voltage-controlled switch comprises a P-channel JFET in series with the current source
Data Source
AI summary
An active capacitor discharging circuit for a power supply can include a current source adapted to be coupled between one or more capacitors and ground; and a voltage-controlled switch that selectively opens responsive to the power supply operating to reduce power consumed by the current source and selectively closes responsive to the power supply not-operating to allow the current source to discharge the one or more capacitors. The current source can include a depletion mode MOSFET coupled to a source resistance such that a channel of the depletion mode MOSFET is in series with the source resistance and a distal terminal of the source resistance is coupled to a gate of the depletion mode MOSFET. The voltage-controlled switch can include a P-channel JFET in series with the current source.