Start-up Circuit Using Depletion Mode Transistor

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Solution Overview

Problem

Existing start-up circuits for power supply in integrated circuits face issues of high power consumption and heat generation due to the use of resistors, and previous solutions with more complex structures are not satisfactory in terms of simplicity and efficiency.

Innovation Solution

A start-up circuit utilizing a depletion mode transistor and an enhancement mode transistor connected partially in parallel, where the depletion mode transistor is normally ON and controls the enhancement mode transistor, eliminating the need for resistors and simplifying the circuit structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a high resistance resistor is used to limit current in the start-up circuit, then power consumption is reduced, but the area of the resistor becomes very large and heat generation increases

Engineering Contradiction:

Improvepower consumptionVSAvoidresistor area

Core Design Contradiction:

Use of energy by moving objectVSArea of stationary object

Solution Approach 1:

The patent removes the resistor from the start-up circuit entirely and replaces it with a depletion mode MOSFET. This extraction of the problematic component (resistor) eliminates the area and heat generation issues while maintaining the current limiting function through the MOSFET's inherent characteristics.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the component type from a passive resistor to an active depletion mode MOSFET, utilizing the MOSFET's voltage-controlled resistance characteristic. By controlling the gate voltage, the MOSFET can dynamically adjust its resistance to limit current during start-up while occupying minimal area and generating minimal heat.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If a high resistance resistor is used to limit current in the start-up circuit, then power consumption is reduced, but heat generation becomes serious

Engineering Contradiction:

Improvepower consumptionVSAvoidheat generation

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the passive resistive element with an active field-effect transistor, using electric field control (gate voltage) to regulate current flow. This substitution allows for much more efficient current control with significantly reduced power dissipation and heat generation compared to a resistive approach.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Use of energy by moving object

If a complex control circuit is used to automatically turn off the start-up circuit, then power consumption is reduced after start-up, but the circuit structure becomes too complicated

Engineering Contradiction:

Improvepower consumptionVSAvoidcircuit structure

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent employs a depletion mode MOSFET that is inherently capable of self-turning off. The MOSFET's gate is connected to its drain through a capacitor, creating a self-biasing mechanism. When the start-up current charges the capacitor, the gate voltage rises, automatically turning off the MOSFET and eliminating the need for external control circuits.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The depletion mode MOSFET performs multiple functions: it limits current during start-up, provides the necessary gate voltage to turn on the enhancement mode MOSFET, and automatically turns off when the start-up is complete. This multi-functionality eliminates the need for separate control circuits, simplifying the overall design.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces power consumption and heat dissipation by eliminating resistors and simplifying the circuit structure, while maintaining effective start-up functionality without complex control mechanisms.

Implementation Method 1

a start-up control element, that is, a depletion mode transistor, having a conduction capability controllable by a voltage applied to a gate

Methodology Applied

Scientific EffectField effect: Electric Field

Implementation Method 2

an enhancement mode transistor, having a conduction capability controllable by a voltage applied to a gate

Methodology Applied

Scientific EffectField effect: Electric Field

Implementation Method 3

charge the capacitor C until the voltage at the node Vbias reaches a predetermined value that is able to turn ON the power circuit 200

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS7843017B2Start-up control device

Publication Date: 2010.11.30 RICHTEK TECH

AI summary

A transistor having a start-up control element is provided. The transistor includes an N-type depletion mode transistor and an N-type enhancement mode transistor. The N-type depletion mode transistor includes a drain for electrically connecting to an external power supply, and a gate normally grounded. The N-type enhancement mode transistor includes a drain electrically connected to the external power supply, and a gate electrically connected to a source of the depletion mode transistor.