DC-DC Regulator Third Transistor Dead Time Efficiency
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Solution Overview
Problem
Step-down type DC-DC regulators face efficiency deterioration due to dead time, where transistors are simultaneously turned off, leading to heat generation and loss, and existing solutions like schottky barrier diodes are expensive and have limited high withstand voltage products.
Innovation Solution
Incorporating a third transistor with a gate voltage less than its threshold voltage to maintain current flow during dead time, eliminating the need for expensive schottky barrier diodes and improving efficiency by using power MOS or GaN HEMT transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dead time is provided to prevent simultaneous turn-on of transistors, then short circuit between power supply line and reference voltage line is prevented, but efficiency deteriorates due to loss generation during dead time
Solution Approach 1:
A third transistor is introduced as an intermediary component to maintain current flow during the dead time period. This additional transistor acts as a mediator that keeps the current path active between the inductor and load, preventing efficiency loss while the primary transistors are both off, thus resolving the contradiction between preventing short circuits and maintaining efficiency.
2Loss of energy
If a schottky barrier diode is provided to make return current flow during dead time, then efficiency deterioration is improved, but cost increases and high withstand voltage products are limited
Solution Approach 1:
The invention replaces the expensive schottky barrier diode with a third transistor that can be implemented using standard power MOS or GaN HEMT technology. This transistor serves the same functional purpose of maintaining current flow during dead time but can be manufactured more cost-effectively and is available in higher voltage ratings, thus resolving the cost and availability contradiction.
3Ease of manufacture
If body diode of second transistor is used instead of schottky barrier diode, then cost is reduced, but reverse recovery time is long and forward drop voltage is large reducing efficiency improvement
Solution Approach 1:
The invention changes the operational parameters of the second transistor by applying a gate voltage that is less than its threshold voltage during dead time. This parameter adjustment allows the transistor to conduct current with much lower forward drop voltage and without the long reverse recovery time issues of body diodes, thus simultaneously achieving cost reduction and efficiency improvement.
Data Source
AI summary
A first transistor coupled between a power supply line and an inductor, a second transistor coupled between a source of the first transistor and a reference voltage line, and a third transistor coupled between the source of the first transistor and a load are included, and efficiency deterioration caused by a dead time is improved by keeping a current flow through a current path of an inductor, a load, and the third transistor during the dead time by supplying a voltage which is less than a threshold voltage and approximately the threshold voltage to a gate of the third transistor as a gate voltage.