RTC Battery Voltage Control Circuit with Low Drop Switching

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Solution Overview

Problem

Blocking diodes used in real-time-clock (RTC) systems for automotive applications result in significant power dissipation due to their fixed voltage drop, making them unsuitable for low voltage and high current applications, leading to reduced operating range and increased thermal management needs.

Innovation Solution

A control circuit and switching circuit system that selectively connects the RTC battery to the RTC power pin with a minimal voltage drop of about 0.1 volts when the primary power supply is unavailable, using a combination of bipolar junction transistors (BJTs) and metal-oxide semiconductor field-effect transistors (MOSFETs) to manage power delivery and inhibit reverse power flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If blocking diodes are used to protect against reverse battery connections, then protection is provided, but significant power dissipation occurs due to fixed voltage drop

Engineering Contradiction:

Improveprotection against reverse battery connectionsVSAvoidpower dissipation

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent changes the electrical parameters of the protection circuit by using MOSFETs with dynamically adjustable resistance instead of fixed diode voltage drops. The control circuit monitors battery voltage and adjusts the MOSFET resistance to provide protection while minimizing power dissipation during normal operation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The protection circuit transitions from a static diode-based approach to a dynamic MOSFET-based system where the resistance can be adjusted in real-time based on operating conditions. The control circuit actively manages the MOSFET gate voltage to optimize both protection and power efficiency under varying load and voltage conditions.

Inventive Principle:

Principle #15Dynamics

2Reliability

If blocking diodes are used in low voltage applications, then protection is provided, but operating range is reduced due to voltage drop

Engineering Contradiction:

Improveprotection against reverse battery connectionsVSAvoidoperating range

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent dynamically changes the voltage drop parameter from the fixed 0.5-0.7V of diodes to a variable resistance of the MOSFETs, which can be adjusted to maintain minimal voltage drop even in low voltage conditions. The control circuit ensures the MOSFET operates in a region that preserves operating range while providing necessary protection.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The control circuit acts as an intermediary between the battery and the protected circuitry, using intelligent control logic to manage the MOSFET switching and resistance adjustment. This intermediary layer provides protection while optimizing power delivery and maintaining operating range under varying voltage conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If blocking diodes are used in high current applications, then protection is provided, but thermal management requirements increase due to power dissipation

Engineering Contradiction:

Improveprotection against reverse battery connectionsVSAvoidthermal management requirements

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent changes the resistance parameter of the protection element from the fixed forward voltage drop of diodes to the controllable on-resistance of MOSFETs. At high currents, the MOSFET's low on-resistance dramatically reduces power dissipation (P=I²R) compared to diodes, thereby reducing heat generation and simplifying thermal management.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful effect of high current through protection elements into a benefit by using MOSFETs whose low on-resistance at high currents minimizes power dissipation and heat generation. The control circuit ensures optimal MOSFET operation to maximize this benefit while maintaining protection functionality.

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 solution minimizes power dissipation and maintains continuous RTC operation with minimal voltage drop, ensuring accurate timekeeping even during primary power supply failures, while preventing reverse power flow and reducing thermal management requirements.

Implementation Method 1

The switching circuit is structured to provide communication between the real-time-clock battery and a real-time-clock power pin of a controller with a voltage drop of about 0.1 volts or less when the control circuit is in the ON arrangement

Methodology Applied

Scientific EffectElectrical Conduction: Conduction (electrical)

Data Source

PatentUS11579651B2Low drop real-time-clock battery voltage control circuit for application specific integrated circuit in an engine control module

Publication Date: 2023.02.14 CUMMINS INC

AI summary

Systems and apparatuses include a circuit structured to communicate with a real-time-clock battery and to selectively communicate with a vehicle battery, inhibit communication between the real-time-clock battery and a controller when a first voltage is received from the vehicle battery, and provide a communication from the real-time-clock battery to the controller when the first voltage is not received.