Current Detection Circuit for Switching Regulators
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Solution Overview
Problem
Existing current detection circuits in switching regulators face inefficiencies due to power losses and increased costs from using series resistors for current sampling, which are exacerbated by the need for low resistance values and additional amplifiers to manage these losses, and also introduce noise and reliability issues.
Innovation Solution
A current detection circuit that employs a mirror circuit to mirror the current through a main power transistor, allowing for average value calculations based on switching cycles and conduction duty cycles to determine input and output currents, thereby eliminating the need for series-connected sampling resistors and reducing power losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If series resistors are used for current sampling, then current detection can be achieved, but power losses increase and costs increase
Solution Approach 1:
The patent introduces an auxiliary transistor as an intermediary element to sense the current through its voltage drop, rather than using a series resistor directly in the main current path. The auxiliary transistor's base-emitter voltage serves as the sensing signal, eliminating the need for power-dissipating series resistors while maintaining detection capability
Solution Approach 2:
The patent replaces the traditional resistive voltage drop method (Ohm's law-based mechanical/electrical system) with a transistor-based voltage sensing method. Instead of measuring voltage across a resistor, the system uses the transistor's inherent base-emitter voltage characteristic to detect current, substituting a more efficient electronic sensing mechanism
2Loss of energy
If low resistance values are used for sampling resistors, then power losses are reduced, but detection precision deteriorates
Solution Approach 1:
The auxiliary transistor acts as an intermediary that amplifies the sensing effect. By using the transistor's current amplification property (beta factor), a small base current can control a larger collector current, allowing accurate detection without requiring large voltage drops across sampling elements, thus avoiding the trade-off between low resistance and detection precision
3Loss of energy
If additional amplifiers are added to manage power losses, then power loss management improves, but device complexity increases
Solution Approach 1:
The auxiliary transistor inherently provides the sensing function through its own electrical characteristics without requiring external amplifiers or additional active components for signal conditioning. The transistor's natural operation generates the sensing voltage, making the system self-sufficient and reducing overall circuit complexity
Solution Approach 2:
The auxiliary transistor serves multiple functions simultaneously: it acts as a current sensor, a signal generator, and a protective element. This multi-functionality eliminates the need for separate amplifiers and signal conditioning circuits, reducing device complexity while effectively managing power loss
4Measurement precision
If series resistors are used for current sampling, then current detection is achieved, but noise and reliability issues increase
Solution Approach 1:
The auxiliary transistor serves as an intermediary sensing element that is electrically isolated from the high-current main path. This isolation prevents the introduction of noise and reliability issues associated with placing resistive elements directly in the power circuit, while still providing accurate current detection through the transistor's controlled voltage output
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 reduces power losses and implementation costs by indirectly obtaining current information without resistors, enhancing the efficiency and reliability of current detection in switching regulators.
Implementation Method 1
a mirror circuit configured to mirror a current flowing through a main power transistor of the switching regulator to generate a sampling signal that is in proportion to the main power transistor current
Data Source
AI summary
In one embodiment, a current detection circuit configured to determine an input current and an output current of a switching regulator, can include: (i) a mirror circuit configured to mirror a current flowing through a main power transistor of the switching regulator to generate a sampling signal that is in proportion to the main power transistor current; (ii) a current generating circuit configured to perform a first average value calculation of the sampling signal based on a switching cycle of the switching regulator to determine the input current; and (iii) the current generating circuit being configured to perform a second average value calculation of the sampling signal based on a conduction duty cycle of the main power transistor to determine the output current.