DC Power Isolation Circuit with Comparator Control

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Solution Overview

Problem

Conventional electrical isolation methods for DC power sources, such as those used in brushless DC motors, fail to fully prevent backflow of induced current from the motor into the power supply, leading to potential damage during normal operations.

Innovation Solution

An electrical isolation circuit comprising a switch and a comparator that compares the voltage of the DC power source and the electrical application, causing the switch to turn off when the application's voltage exceeds the power source's voltage, thereby preventing current flow back into the power supply.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a MOSFET is used for electrical isolation, then voltage drop and power dissipation are reduced, but backflow of induced current into the DC power source cannot be fully prevented

Engineering Contradiction:

Improvepower dissipationVSAvoidprotection against backflow current

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent introduces a diode as an intermediary component between the MOSFET and the DC power source. This diode acts as a mediator that allows the MOSFET to maintain low power dissipation while the diode provides the necessary electrical isolation to prevent backflow of induced current into the power source.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a Shottky diode is used for electrical isolation, then backflow of induced current is prevented, but voltage drop and power dissipation increase

Engineering Contradiction:

Improveprotection against backflow currentVSAvoidpower dissipation

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent combines a MOSFET and a diode into a single isolation circuit stage. The MOSFET handles the main current flow with low resistance, while the diode provides protection against reverse current. This merging of components achieves both low power dissipation and reliable backflow prevention.

Inventive Principle:

Principle #5Merging (Combining)

3Ease of operation

If electrical isolation is implemented using conventional methods, then some protection is provided, but the DC power supply may still be damaged by induced current during normal operations

Engineering Contradiction:

Improveisolation functionalityVSAvoiddamage to power supply

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent implements preliminary protection by placing the diode in series with the MOSFET output before the current can reach the DC power source. This preliminary action ensures that any induced current generated during normal MOSFET operation is blocked before it can cause damage to the power supply.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS7800322B2Isolation circuit for DC power sources

Publication Date: 2010.09.21 STMICROELECTRONICS INT NV

AI summary

The electrical isolation circuit of the present disclosure includes a switch coupled between the DC power source and the electrical application and a comparator for controlling the switch by receiving inputs from the DC power source and the electrical application. The comparator causes the switch to switch ON when the DC power source has a higher voltage than the electrical application allowing the normal operation of the electrical application. However, when the electrical application has a higher voltage than the DC power source, the comparator causes the switch to switch OFF thereby preventing flow of current from the electrical application to the DC power source.