Switch Driver Circuit With Variable Slew Rate For Fast Turn-On

Solution Overview

Problem

Existing transistor driver circuits face challenges in quickly turning on switching elements like FETs due to parasitic capacitance, which can lead to longer turn-on times and stability issues, and fast switching can cause electromagnetic interference, violating compliance standards.

Innovation Solution

A driver circuit with a variable slew rate is implemented, using a combination of high and low impedance driver circuit portions to rapidly turn on the transistor, with the high impedance portion responsible during the initial turn-on phase and the low impedance portion assisting to overcome capacitance limitations, while ensuring stability by disabling the low impedance portion once the desired turn-on characteristic is achieved.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the slew rate of the control signal is increased to reduce turn-on time, then the turn-on speed of the FET is improved, but stability issues arise and electromagnetic interference is exacerbated

Engineering Contradiction:

Improveturn-on speedVSAvoidcircuit stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The driver circuit is divided into two distinct portions: a first driver circuit portion with higher output impedance and a second driver circuit portion with lower output impedance. This segmentation allows each portion to be optimized for different aspects of the switching operation, enabling fast turn-on while maintaining stability through the higher impedance portion during critical transitions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit dynamically switches between the first and second driver circuit portions based on the switching state. A switch controller enables the second driver circuit portion during turn-on to provide fast charging, then disables it during steady-state operation, allowing the first driver circuit portion to maintain stability. This dynamic configuration optimizes both speed and stability at different operational phases.

Inventive Principle:

Principle #15Dynamics

2Speed

If the slew rate of the control signal is increased to reduce turn-on time, then the turn-on speed of the FET is improved, but electromagnetic interference is exacerbated

Engineering Contradiction:

Improveturn-on speedVSAvoidelectromagnetic interference

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The driver circuit is divided into two distinct portions: a first driver circuit portion with higher output impedance and a second driver circuit portion with lower output impedance. This segmentation allows each portion to be optimized for different aspects of the switching operation, enabling fast turn-on while maintaining stability through the higher impedance portion during critical transitions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit dynamically switches between the first and second driver circuit portions based on the switching state. A switch controller enables the second driver circuit portion during turn-on to provide fast charging, then disables it during steady-state operation, allowing the first driver circuit portion to maintain stability. This dynamic configuration optimizes both speed and stability at different operational phases.

Inventive Principle:

Principle #15Dynamics

3Productivity

If a single driver circuit portion is used, then the device complexity is reduced, but the ability to achieve both fast turn-on and stability is compromised

Engineering Contradiction:

Improveturn-on efficiencyVSAvoiddriver circuit complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The driver circuit is divided into two distinct portions: a first driver circuit portion with higher output impedance and a second driver circuit portion with lower output impedance. This segmentation allows each portion to be optimized for different aspects of the switching operation, enabling fast turn-on while maintaining stability through the higher impedance portion during critical transitions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first and second driver circuit portions are merged into a single integrated driver circuit that can operate in different configurations. The switch controller manages the interaction between the two portions, enabling them to work together during turn-on and separately during steady-state operation, thus achieving high productivity without excessive complexity.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS9379708B2Switch driver circuit and associated methods

Publication Date: 2016.06.28 ALLEGRO MICROSYSTEMS LLC

AI summary

A driver circuit for driving a switch includes a high output impedance driver circuit portion having a high impedance output node coupled to the control terminal of the transistor and a low output impedance driver circuit portion having a low impedance output node also coupled to the control terminal of the transistor. The slew rate of the control signal is established by at least one of the high impedance driver circuit portion and the low impedance driver circuit portion.