DC-DC Converter Gate Drive for Reverse Recovery Suppression
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Solution Overview
Problem
The reverse recovery current in DC-DC converters can cause voltage ringing and potential damage to transistors due to large di/dt, exceeding their breakdown voltage, especially in high-side power transistors with body diodes.
Innovation Solution
A driver circuit maintains high-side power transistors in a low-conductivity state by discharging the gate-to-source voltage to an intermediate level, preventing current flow through the body diode and reducing reverse recovery current, thereby mitigating shoot-through paths and voltage instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If high-side power transistors are fully conductive to reduce on-resistance losses, then power efficiency is improved, but reverse recovery current increases causing voltage ringing and potential transistor damage
Solution Approach 1:
The driver circuit performs preliminary action by discharging the gate-to-source voltage to an intermediate level before the transistor is fully turned off. This preliminary reduction of conductivity prevents the body diode from conducting heavily, thereby reducing reverse recovery current when the transistor switches off, while maintaining sufficient conductivity during the on-state to minimize on-resistance losses
Solution Approach 2:
The invention changes the parameter of gate-to-source voltage from a binary state (fully on/fully off) to a three-state system (intermediate level). By controlling the gate voltage to an intermediate level during specific periods, the transistor operates in a low-conductivity state that reduces reverse recovery current while still allowing current flow through the channel rather than the body diode
2Object-affected harmful factors
If gate-to-source voltage is discharged to intermediate level to reduce reverse recovery current, then reverse recovery current is reduced, but transistor conductivity decreases
Solution Approach 1:
The invention applies local quality by creating different conductivity states at different times. During the on-state, the transistor maintains high conductivity for efficient power transmission. During the transition and off-state, the transistor operates in a low-conductivity state with gate voltage at intermediate level to reduce reverse recovery current. This temporal differentiation of conductivity quality resolves the contradiction between reducing harmful currents and maintaining reliability
3Strength
If body diode conducts current to provide low-side clamp, then voltage clamping is improved, but reverse recovery current increases causing shoot-through paths
Solution Approach 1:
The driver circuit applies preliminary anti-action by proactively reducing the gate-to-source voltage to an intermediate level before the body diode can conduct significant current. This preventive measure counteracts the tendency of the body diode to conduct and cause reverse recovery issues, while still maintaining sufficient voltage clamping capability through the transistor channel
Data Source
AI summary
In some examples, a circuit includes a first transistor having first and second terminals; a first current source having first and second terminals, the first terminal of the first current source coupled to the first terminal of the first transistor, and the second terminal of the first current source coupled to the second terminal of the first transistor; a second transistor having a control terminal and first and second terminals, the control terminal of the second transistor coupled to the second terminal of the first current source, and the first terminal of the second transistor coupled to the second terminal of the first current source; a third transistor having first and second terminals, the first terminal of the third transistor coupled to the second terminal of the second transistor; and a fourth transistor having first and second terminals, the first terminal of the fourth transistor coupled to the second terminal of the first current source, and the second terminal of the fourth transistor coupled to the second terminal of the third transistor.