Reverse Capacitor Voltage Balancing in Charge Pump Circuits
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Solution Overview
Problem
Existing direct current converters often experience high inrush currents in sensitive circuit elements, such as switching transistors, which can lead to inefficiencies and potential damage.
Innovation Solution
A switched capacitor converter design incorporating a primary switching circuit, a flying capacitor circuit, and a secondary switching circuit, with pre-balancing mechanisms to manage the charging and discharging of capacitors, minimizing inrush currents by controlling the switching transistors' duty cycles and using current sources to regulate voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing direct current converters are used for voltage conversion, then voltage conversion function is achieved, but large inrush current occurs in switching transistors causing inefficiency and potential damage
Solution Approach 1:
The patent applies preliminary action by pre-charging the flying capacitors to the input voltage level before the main switching operation begins. This pre-charging phase prepares the capacitors in advance, ensuring that when the main switching starts, no large inrush current will flow through the switching transistors because the voltage difference that would cause inrush current has been eliminated. The control circuit selectively activates pre-charge switches to charge capacitors before enabling the main power switches.
Solution Approach 2:
The patent segments the voltage conversion process into distinct phases: a pre-charge phase where flying capacitors are charged to input voltage level, and a main conversion phase where power is transferred to the output. This segmentation allows the system to prepare components in advance (pre-charge phase) before executing the main function (power conversion), thereby preventing harmful inrush currents during the transition between phases.
2Loss of energy
If inrush current is limited in switching transistors, then efficiency and reliability improve, but voltage conversion capability must be maintained
Solution Approach 1:
The patent maintains full voltage conversion capability by ensuring that before power conversion begins, the flying capacitors are pre-charged to the appropriate voltage level. This preliminary charging action eliminates voltage differences that would cause inrush current, allowing subsequent power transfer operations to proceed efficiently without energy loss. The control circuit manages this timing to ensure both efficiency and full conversion capability are maintained.
Solution Approach 2:
The control circuit acts as an intermediary that coordinates the pre-charging phase and the main power conversion phase. It selectively activates pre-charge switches and main power switches in a controlled sequence, mediating between the need to limit inrush current and the need to maintain full voltage conversion capability. This intermediary control ensures smooth transition between phases without energy loss.
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 effectively reduces inrush currents and enhances the efficiency of DC/DC conversion, maintaining a stable output voltage while limiting the stress on switching transistors, thereby improving the overall performance of the converter without increasing complexity or cost.
Implementation Method 1
a first current source that discharges the flying capacitors via a first path having a body diode of a switching transistor of the primary switching circuit
Implementation Method 2
a second current source that charges the flying capacitors via a second path having switching transistors of the primary switching circuit and the secondary switching circuit
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3C
AI summary
A switched capacitor converter includes a primary switching circuit, a flying capacitor circuit, and a secondary switching circuit. The primary switching circuit includes plurality of switching transistors in series. The flying capacitor circuit includes one or more flying capacitors with each flying capacitor connected to a switching transistor. The secondary switching circuit includes two or more switching transistors and provides a first path for charging and a second path for discharging the flying capacitors. At startup, the flying capacitors are discharged via a first current source while the switching transistors are turned off. After discharging, the flying capacitors are charged via a second current source, while a first switching transistor of the primary switching circuit is kept turned off and the rest of the switching transistors perform switching according to a switching cycle. After charging, the switched capacitor converter may enter a steady state operation.