Reference Circuit Startup Using Diode Voltage Thresholds
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Solution Overview
Problem
Conventional high voltage reference circuits, particularly in automotive applications, face issues with power consumption and startup reliability due to the use of capacitor-based RC delays, which can fail to initiate the circuit if the supply ramp matches the time constant.
Innovation Solution
A reference circuit design incorporating a current mirror, NMOS transistors, zener diodes, and a control circuit with voltage dividers, eliminating the need for large resistors and capacitors, and utilizing diodes to provide a startup current and output voltage while avoiding RC delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitor-based RC delay circuits are used for startup, then startup current can be provided, but the circuit may fail to start if supply ramp matches the time constant and power consumption increases
Solution Approach 1:
The patent extracts and eliminates the capacitor component from the startup circuit, replacing the RC delay mechanism with a diode-based voltage comparison mechanism. This removes the fundamental cause of both the reliability issue (time constant matching supply ramp) and the power consumption issue (large resistor requirements), directly resolving the technical contradiction.
Solution Approach 2:
The patent changes the operational parameters of the startup circuit by using diodes with specific forward voltage drops (0.6V-0.7V) to create voltage thresholds for transistor activation. This parameter-based approach replaces the time-constant-based RC circuit, enabling reliable startup without excessive power consumption regardless of supply ramp characteristics.
2Reliability
If large resistors and capacitors are used in the startup branch, then startup current can be generated, but the circuit area increases and transient load response deteriorates
Solution Approach 1:
The patent removes the large capacitor and large resistor components from the startup branch, replacing them with small-signal transistors and diodes. This extraction eliminates the area-consuming components while maintaining the startup function through a different mechanism (voltage comparison and transistor activation rather than RC charging).
Solution Approach 2:
The patent substitutes the passive RC time-constant mechanism with an active transistor-diode voltage comparison mechanism. This substitution allows the startup function to be achieved with much smaller components, reducing circuit area while improving transient response characteristics.
3Reliability
If RC delay circuits are used for startup, then startup current is provided, but the circuit cannot respond quickly to transient loads due to the time constant
Solution Approach 1:
The patent extracts the capacitor that creates the limiting time constant, replacing it with a diode-based voltage threshold mechanism. This elimination removes the speed-limiting factor while preserving the startup capability through alternative means (voltage comparison and transistor switching).
Solution Approach 2:
The patent introduces dynamic transistor switching controlled by voltage thresholds rather than passive RC charging. The transistors can switch rapidly when voltage thresholds are reached, providing both reliable startup and fast transient response, unlike the fixed time constant of RC circuits.
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 configuration reduces power consumption, eliminates the need for large capacitors, and enhances transient load response by providing a reliable startup current and maintaining output voltage, improving the circuit's startup characteristics and load handling.
Implementation Method 1
a plurality of diodes coupled between the control electrode of the second transistor and the first passive electrode of the second transistor
Implementation Method 2
a reverse-bias zener diode coupled to the resistor, wherein the zener diode has a breakdown voltage of about 6 volts, and wherein the cathode of the zener diode is coupled to the control electrodes of the first and second transistors
Data Source
AI summary
An apparatus is provided. The apparatus comprises a reference circuit and a startup circuit. The reference circuit is adapted to provide a startup current, while the startup circuit receives the startup current and outputs an output voltage. The startup circuit includes a current mirror, a first NMOS transistor, a second NMOS transistor, diodes, and a third NMOS transistor, and a control circuit. The first and second NMOS transistors are coupled to the current mirror at their sources and are coupled to one another and to the reference circuit at their gates. The diodes are coupled between the gate of the second NMOS transistor and the source of the second NMOS transistor, and the third NMOS transistor is coupled to the source of the second NMOS transistor at its gate (which also provides the output voltage at its source). The control circuit is then coupled to the drains of the first and second NMOS transistors.