Boost DC/DC Converter Switch Control for Overvoltage-Free Shutdown

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Solution Overview

Problem

In boost DC/DC converters, safely turning off the load switch and high-side switch is challenging due to the risk of steep coil current changes and overvoltage occurrences when these switches are turned off, which can lead to voltage being supplied to the output line even when the converter is stopped.

Innovation Solution

A control circuit that includes an input pin, a pulse modulator, a logic circuit, and a switch driving circuit to manage the high-side and low-side transistors, applying a voltage corresponding to the input or output voltage to the gate of PMOS or NMOS transistors to prevent immediate switch-off, allowing the transistors to operate as source followers and clamp voltages, thereby reducing coil current and preventing overvoltages.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the load switch or high-side switch is turned off to prevent voltage from being supplied to the load when the boost DC/DC converter is stopped, then the voltage supply to the load is prevented, but a coil current flowing in the inductor steeply changes and an overvoltage occurs

Engineering Contradiction:

Improveprevention of voltage supply to load when stoppedVSAvoidovervoltage occurrence

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The control circuit performs preliminary action by gradually reducing the coil current before turning off the load switch or high-side switch. The current reduction processing is executed in advance to prevent steep current changes and overvoltage when the switch is turned off.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control circuit provides beforehand cushioning by suppressing the steep change of coil current through current reduction processing before the switch turn-off. This cushioning effect prevents overvoltage occurrence that would otherwise happen when the switch is turned off.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Reliability

If the load switch or high-side switch is turned off to prevent voltage from occurring on the output line, then the output line voltage is prevented, but the coil current steeply changes causing potential damage

Engineering Contradiction:

Improveoutput line voltage controlVSAvoidsteep coil current change

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The control circuit performs preliminary action by executing current reduction processing before turning off the load switch or high-side switch. This preliminary current reduction prevents steep current changes when the switch is turned off.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control circuit converts the potentially harmful steep current change into a beneficial gradual current reduction. By controlling the current to decrease gradually before switch turn-off, the harmful effect is transformed into a controlled, safe current transition.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 approach safely turns off the load switch and high-side switch, preventing overvoltages and reducing coil current, thereby enhancing the reliability and efficiency of the DC/DC converter operation without the need for additional circuit elements or components.

Implementation Method 1

allowing the transistors to operate as source followers and clamp voltages, thereby reducing coil current and preventing overvoltages

Methodology Applied

Scientific EffectSource follower operation:

Data Source

PatentUS12149164B2Control circuit and power supply circuit of DC/DC converter, and electronic equipment

Publication Date: 2024.11.19 ROHM CO LTD

AI summary

Disclosed herein is a control circuit of a boost DC/DC converter having a high-side transistor and a low-side transistor. The circuit includes an input pin that receives an input voltage of the boost DC/DC converter, a pulse modulator that generates a pulse signal pulse-modulated in such a manner that output of the boost DC/DC converter comes close to a target state, a logic circuit that generates a control signal of the high-side transistor and a control signal of the low-side transistor on the basis of the pulse signal, and a switch driving circuit that drives a load switch that is a PMOS transistor connected to the high-side transistor and a load between them. When stopping the boost DC/DC converter, the switch driving circuit applies a voltage corresponding to the input voltage of the boost DC/DC converter to a gate of the PMOS transistor.