Body-Controlled Switch With Series Capacitor For Reverse Recovery
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Solution Overview
Problem
Synchronous switching devices, such as synchronous boost converters, experience undesirable power consumption due to the formation of parasitic Bipolar Junction Transistors (BJTs) that create an intrinsic current path even in shutdown conditions, leading to inefficiencies and heat generation, particularly in heat-sensitive and power-sensitive devices.
Innovation Solution
The implementation of body-controlled synchronous switches with a charge-supplying device, like a capacitor, coupled in series between the bulk node and a power node, minimizes recombination time by providing power during reverse recovery of the parasitic device, allowing quicker polarity switching and reduced power consumption, especially under low voltages and heavy loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional body-controlled switches are used, then device complexity is reduced, but power consumption increases due to parasitic BJT current paths
Solution Approach 1:
The capacitor is pre-charged to a voltage higher than the bulk node voltage before reverse recovery occurs. This preliminary charging action ensures that when reverse recovery happens, the capacitor can immediately supply the necessary charge to keep the parasitic BJT reverse-biased, preventing forward conduction and reducing power loss without requiring complex control circuitry.
Solution Approach 2:
The capacitor acts as an intermediary charge storage device between the power supply and the bulk node. It mediates the charge transfer during reverse recovery by providing a local charge reservoir that can quickly supply or absorb charge as needed, isolating the bulk node from direct power supply fluctuations and enabling faster, more efficient polarity switching.
2Speed
If reverse recovery time is reduced, then switching speed improves, but power loss increases due to recombination current
Solution Approach 1:
The capacitor is pre-charged to a voltage higher than the bulk node voltage before reverse recovery occurs. This preliminary charging action ensures that when reverse recovery happens, the capacitor can immediately supply the necessary charge to keep the parasitic BJT reverse-biased, preventing forward conduction and reducing power loss without requiring complex control circuitry.
Solution Approach 2:
The invention changes the voltage parameter of the capacitor to be higher than the bulk node voltage. This parameter change ensures that the capacitor can actively pull the bulk node voltage down during reverse recovery, maintaining reverse bias on the parasitic BJT and reducing both the duration and magnitude of recombination current, thereby reducing power loss while enabling faster switching.
3Loss of energy
If isolation between input and output is improved, then power loss reduces, but device complexity increases due to additional control circuitry
Solution Approach 1:
The invention extracts the charge storage function from the main switch structure and places it in a separate capacitor component. This extraction allows the capacitor to independently manage charge during reverse recovery without requiring complex control circuitry, simplifying the overall device while improving isolation and reducing power loss.
Solution Approach 2:
The capacitor acts as an intermediary charge storage device between the power supply and the bulk node. It mediates the charge transfer during reverse recovery by providing a local charge reservoir that can quickly supply or absorb charge as needed, isolating the bulk node from direct power supply fluctuations and enabling faster, more efficient polarity switching.
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 enhances efficiency by reducing power losses and heat generation, achieving higher efficiency ratings compared to conventional body-controlled switches, particularly at heavier loads and lower operating voltages, as demonstrated by the relative efficiency graphs.
Implementation Method 1
A capacitor having a voltage higher than a bulk node voltage of the synchronous switch is coupled between a power supply and the bulk node
Data Source
AI summary
A synchronous switch uses body-control switches to control the polarity of the parasitic device, which can be used to reduce power consumption by the parasitic device in accordance with various operating conditions. A charge-supplying device (such as a capacitor) is coupled in series between the bulk node (of the synchronous switch) and a power node (such as Vout or ground). The charge-supplying device provides power to the bulk node of the switch during reverse recovery of the parasitic device to minimize recombination time. Minimizing recombination time allows the polarity of the parasitic device to be switched more quickly (especially under low operating voltage and/or heavy load conditions), which converses more power.