Dead Time Modulation for SMPS Switching Loss Reduction
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Solution Overview
Problem
Conventional switched mode power supplies (SMPSs) face significant switching losses due to high input voltages and high frequencies, particularly with low input voltages and high frequencies, which result in inefficiencies and substantial losses.
Innovation Solution
The proposed SMPS employs a switching circuit with a controller that utilizes a negative inductor current to control the slewing of the switching node voltage, incorporating a high-side and low-side transistor, a diode, and a variable capacitor to achieve high conversion efficiency by optimizing the switching frequency and input voltage, thereby overcoming losses incurred by using the negative inductor current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional switching circuits are used with high input voltages and high frequencies, then power conversion capability is improved, but switching losses due to output capacitance become large
Solution Approach 1:
The controller initiates a dead time interval before the main switching action occurs. During this dead time, the switching node voltage is pre-charged or pre-discharged using the negative inductor current, so that when the switch actually turns on or off, the voltage stress and switching losses are minimized. This preliminary action prepares the switching node in advance to reduce energy dissipation during the actual switching event.
Solution Approach 2:
The invention converts the harmful negative inductor current, which traditionally causes losses during dead time, into a beneficial resource. Instead of allowing this current to flow through lossy paths, the controller utilizes it to actively slew the switching node voltage during dead time intervals, transforming what was previously a source of inefficiency into a mechanism that reduces overall switching losses by minimizing voltage stress during switching transitions.
2Loss of energy
If dead time is extended to reduce switching losses, then switching losses are reduced, but conversion efficiency deteriorates due to increased dead time losses
Solution Approach 1:
The negative inductor current during dead time, which traditionally represents lost energy, is converted into a useful resource. The controller utilizes this current to actively charge or discharge the switching node capacitance during dead time intervals, transforming the dead time from a purely lossy period into a productive phase that prepares the switching node for the next switching event, thereby reducing overall switching losses without proportionally increasing dead time losses.
Solution Approach 2:
The controller dynamically adjusts the switching node voltage trajectory during dead time by controlling the flow of negative inductor current. By changing the voltage slew rate and timing parameters during dead time intervals, the system optimizes the balance between reducing switching losses and minimizing dead time losses, achieving better overall efficiency compared to conventional fixed dead time approaches.
Data Source
AI summary
A method for generating an output voltage from an input voltage with a switched mode power supply at a switching frequency is provided. At the switching frequency, a transistor within a switching circuit is deactivated so as to enter into a dead time interval, where the switching circuit includes a switching node. A negative inductor current is used during the dead time interval so as to slew the switching node, where switching frequency and the input voltage are sufficiently large so as to overcome a loss incurred by using the negative inductor current.