DC/DC Converter Reverse Recovery Charge Elimination
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Solution Overview
Problem
Switching mode power converters face efficiency losses due to the reverse recovery charge phenomenon, particularly in synchronous DC/DC power converters, where the parasitic body diode of the low-side switching transistor experiences high diode conduction and thermal stress, limiting switching frequency and preventing size reduction of the converter.
Innovation Solution
The solution involves a switching mode power converter circuit with a configuration of two high-side and two low-side transistor switches, where the first high-side and low-side switches have larger on-state resistance than the second ones, and a control circuit that manages their states to avoid parasitic body diode conduction, allowing both small high-side and low-side switches to be in the on-state simultaneously, thus minimizing reverse recovery charge and improving efficiency without additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the low-side switching transistor is turned OFF and the high-side switching transistor is turned ON, then the switching operation continues, but reverse recovery charge accumulates in the parasitic body diode causing efficiency loss
Solution Approach 1:
The patent segments the low-side switching transistor into two parallel paths: one through the controlled switching transistor and another through the parasitic body diode. By providing an alternative current path, the segmentated structure allows current to bypass the body diode during critical switching transitions, eliminating reverse recovery charge accumulation while maintaining continuous current flow.
Solution Approach 2:
The patent introduces an intermediary circuit element (the parallel-connected switching transistor) that mediates the current flow between the inductor and ground. This intermediary provides a controlled path for inductor current during the transition period, preventing the current from forcing the body diode into conduction and subsequent reverse recovery.
2Loss of energy
If additional components like Schottky diodes are added to eliminate reverse recovery charge, then efficiency improves, but device complexity and cost increase
Solution Approach 1:
The patent makes the low-side switching transistor multi-functional by having it serve both as the primary switching element and as providing an alternative current path through its parallel connection. This universal approach eliminates the need for separate Schottky diodes or additional body diode elimination components, as the switching transistor itself provides the necessary current diversion function.
Solution Approach 2:
The patent employs the existing low-side switching transistor to solve its own reverse recovery problem. By configuring the transistor in a parallel arrangement with itself (effectively creating two identical switching transistors in parallel), the circuit uses the switching device's own characteristics to prevent body diode conduction, eliminating the need for external components.
3Reliability
If the body diode conducts during dead time, then the freewheeling current has a path, but thermal stress and power dissipation increase
Solution Approach 1:
The patent segments the current path into two separate parallel pathways: one through the body diode and another through the controlled switching transistor. This segmentation allows the current to be divided and routed through the lower-resistance switching transistor path during dead time, reducing the current burden on the body diode and minimizing thermal stress.
Solution Approach 2:
The patent changes the electrical parameters of the current path by introducing a parallel switching transistor with controlled resistance. This parameter change provides a low-impedance alternative path that reduces voltage drop and power dissipation compared to the high forward voltage drop of the body diode, thereby reducing thermal stress.
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 configuration effectively reduces power dissipation and improves overall efficiency by limiting current flow through small transistor switches, avoiding reverse recovery charge buildup, and does so without requiring external components like Schottky diodes, thus maintaining cost-effectiveness and silicon area efficiency.
Implementation Method 1
MOSFET parasitic body diode reverse recovery occurs during diode switching from the ON state to the OFF state since its stored minority charges must be removed
Implementation Method 2
During these periods, the output inductor produces a freewheeling current that flows through the body diode of the low-side switching transistor
Implementation Method 3
The switching transistors are alternatively activated (e.g., placed in the ON state), providing energy to a load, through the output inductor and across the output filter capacitor
Data Source
AI summary
A switching mode power converter circuit is disclosed, comprising a first high-side switch and a first low-side switch coupled in series between an input voltage level and a reference voltage level, a second high-side switch and a second low-side switch coupled in series between the input voltage level and the reference voltage level, and a control circuit for controlling switching operation of the first and second high-side switches and the first and second low-side switches. The first high-side switch has a larger on-state resistance than the second high-side switch and the first low-side switch has a larger on-state resistance than the second low-side switch. The control circuit is configured to, during an on-state of the first and second low-side switches, control the second low-side switch to switch to the off-state and control the first high-side switch to switch to the on-state, so that the first high-side switch and the first low-side switch are both in the on-state. The application further relates to a method of operating such switching mode power converter circuit.