Reverse X2 Charge Pump Soft Start Circuit
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Solution Overview
Problem
Switched-mode power supply circuits operating in reverse multiply-by-two (X2) mode face challenges with excessive startup currents and large voltage changes during startup, which can stress circuit components and lead to potential damage.
Innovation Solution
The implementation of a soft start mechanism that gradually increases the middle input voltage from the output voltage to twice the output voltage, using a current sink and specific transistor configurations to manage the charging of capacitors and inductors, thereby avoiding sudden power-on stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a switched-mode power supply circuit operates in reverse multiply-by-two mode without soft start, then the circuit can immediately provide full power output, but excessive startup currents and large voltage changes occur that stress circuit components
Solution Approach 1:
The patent applies preliminary action by implementing a soft start mechanism that gradually increases the middle input voltage from the output voltage to twice the output voltage before full operation begins. This preliminary voltage ramping prevents excessive inrush currents and large voltage changes that would otherwise occur at power-on, protecting circuit components while still enabling subsequent full power output.
2Reliability
If a current sink is used to gradually increase voltage during soft start, then startup current is controlled, but the circuit requires additional control phases and transistor switching sequences
Solution Approach 1:
The patent applies segmentation by dividing the soft start process into distinct phases controlled by different transistor switching sequences. The first phase uses a first set of transistors to initially charge the capacitive element, while the second phase uses a second set of transistors to complete the voltage ramping. This segmentation allows complex voltage control to be achieved through manageable, discrete switching stages rather than a single complex control circuit.
3Adaptability or versatility
If the charge pump circuit is reconfigured to connect the capacitor in series with the supply and load to double the voltage, then the voltage multiplication function is achieved, but large voltage changes occur during the two-stage cycle transition
Solution Approach 1:
The patent applies beforehand cushioning by using the soft start mechanism to gradually prepare the circuit for voltage multiplication before the actual two-stage cycle begins. The capacitive element is pre-charged to the output voltage, and the middle input voltage is gradually increased to twice the output voltage during controlled phases. This cushioning effect prevents large voltage transients and instability that would occur during abrupt reconfiguration from parallel to series connection.
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 approach prevents excessive current and voltage surges, allowing for safe startup and reducing the risk of switcher damage, while also enabling the charge pump to operate effectively in reverse X2 mode without external load switches.
Implementation Method 1
a capacitive element having a first terminal coupled to the first node and having a second terminal coupled to the third node
Data Source
AI summary
Certain aspects of the present disclosure generally relate to soft starting a switched-mode power supply (SMPS) circuit operating as a charge pump in a reverse multiply-by-two mode. One example SMPS circuit generally includes a plurality of transistors, a capacitive element coupled to the plurality of transistors, and a current sink coupled between the capacitive element and a reference potential node for the SMPS circuit. For certain aspects, the current sink is configured to be enabled during a first phase of a soft start operation for the SMPS circuit, but is configured to be disabled during a second phase of the soft start operation and during normal operation for the SMPS circuit.