Capacitor Charging Circuit with Spike-Immune Voltage Sensing
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Solution Overview
Problem
Conventional capacitor charging circuits face challenges in accurately determining when a capacitor is fully charged, as voltage spikes during switch-off can lead to incorrect output voltage sensing, and existing solutions do not effectively address the reverse recovery time of diodes, which slows down charging.
Innovation Solution
The proposed solution includes a primary side output voltage sensing circuit with a filter to eliminate voltage spikes and a comparator responsive to both switch voltage and secondary current, ensuring accurate charging completion. Additionally, an auxiliary switch is used in parallel with the main switch to reduce diode reverse recovery time, speeding up the charging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sensing is performed during switch-off, then output voltage can be monitored, but voltage spikes cause incorrect sensing results
Solution Approach 1:
The patent extracts the voltage sensing function from the switch-off period and performs it during the switch-on period instead. The output voltage is sensed during when the switch is closed, avoiding the harmful voltage spikes that occur during switch-off. This temporal separation of the sensing operation from the harmful event resolves the contradiction between being able to monitor voltage and avoiding spike-induced errors.
2Productivity
If diode reverse recovery time is reduced, then charging speed increases, but additional circuit complexity is required
Solution Approach 1:
The patent segments the switching function by introducing a second switch that operates in parallel with the diode during specific phases. This segmentation allows the diode's reverse recovery issue to be bypassed by providing an alternative current path through the second switch, thereby reducing the effective reverse recovery time impact while managing the added circuit complexity through functional division.
Solution Approach 2:
The second switch acts as an intermediary element that mediates between the diode's reverse recovery limitation and the desired fast charging performance. By introducing this intermediate switching device, the system can transfer energy to the capacitor more quickly without being constrained by the diode's inherent reverse recovery time, thus improving charging speed while accepting controlled increases in circuit complexity.
3Productivity
If switch on time is extended to charge capacitor faster, then charging speed improves, but voltage sensing accuracy during switch-off deteriorates
Solution Approach 1:
The patent performs voltage sensing as a preliminary action during the switch-on period before the switch-off and its associated voltage spikes occur. By sensing the output voltage in advance during when the switch is closed and conditions are stable, the system can determine charging status without being affected by subsequent voltage spikes, thus maintaining sensing accuracy while allowing extended switch-on time for faster charging.
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 provides accurate and efficient capacitor charging by eliminating voltage spike-induced errors and reducing diode reverse recovery time, resulting in faster charging times and reliable full-charge detection.
Implementation Method 1
a filter coupled to the switch to provide a filtered switch voltage signal
Implementation Method 2
a comparator responsive to the filtered signal and to a reference voltage to provide a control signal indicative of whether the output voltage of the capacitor charging circuit has reached a desired level
Implementation Method 3
an auxiliary switch coupled in parallel with the main switch and adapted to be on when current through the capacitor is less than a predetermined level and off when the capacitor current is greater than the predetermined level. With this arrangement, the reverse recovery time of the diode is reduced
Data Source
AI summary
A capacitor charging circuit is provided with a primary side output voltage sensing circuit for generating a control signal indicative of whether the output voltage has reached a desired level. The control signal is unaffected by voltage spikes occurring when the main switch is turned off. In one embodiment, the circuit filters the primary side voltage for comparison to a reference voltage in order to provide the control signal. In another embodiment, an AND gate provides the control signal indicating that the output voltage has reached the desired level only in response to the primary side voltage being greater than a reference voltage and the secondary current being discontinuous. In a further embodiment, an AND gate provides the control signal indicating that the output voltage has reached the desired levels only in response to a predetermined delay occurring after the primary side voltage becomes greater than a reference voltage and the secondary current being discontinuous. According to a further aspect of the invention, an auxiliary switch is provided to reduce the reverse recovery time of the output diode in order to speed up the capacitor charging time.