Non-isolated AC-to-DC Converter Charging Circuit
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Solution Overview
Problem
Existing power supply circuits for microcontroller integrated circuits are inefficient, particularly linear regulators which have low efficiency and flyback converters that are costly and inefficient during startup, and frequently powered up and down, leading to low overall efficiency.
Innovation Solution
A power supply circuit comprising a bridge rectifier, a charging circuit, and a storage capacitor, where the charging circuit is activated only when the input voltage is slightly higher than the output voltage, using a depletion mode n-channel field effect transistor and a voltage detector circuit to control charging current, and varying the charging current magnitude based on the output voltage to minimize power dissipation and noise injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a linear regulator is used to supply power to a microcontroller, then the circuit is simple and low cost, but the power efficiency is extremely low (0.1% efficiency) due to large voltage drop across the regulator
Solution Approach 1:
The patent changes the operating parameters of the power supply by using a switching regulator instead of a linear regulator, operating at high frequency with pulse-width modulation to achieve high efficiency while maintaining simplicity. The switching regulator converts power with minimal loss by storing energy in inductors and capacitors during switching cycles.
Solution Approach 2:
The patent replaces the linear mechanical voltage dropping mechanism with an electronic switching mechanism using MOSFETs and control logic, enabling efficient power conversion through electronic switching rather than resistive voltage drop.
2Loss of energy
If a flyback converter is used to improve power efficiency, then power efficiency improves (80-85% in steady state), but the device becomes more complex and costly due to requiring transformers and auxiliary windings
Solution Approach 1:
The patent extracts and eliminates the transformer component from the power supply circuit, using only inductors and capacitors for energy storage and transfer. This simplifies the circuit while maintaining switching regulator efficiency, removing the need for expensive magnetic components and auxiliary windings.
Solution Approach 2:
The patent uses inexpensive surface-mount inductors and capacitors instead of expensive transformers, accepting that these smaller components may have slightly different characteristics but achieving overall cost reduction and simplified design.
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
The solution achieves high efficiency by charging the storage capacitor only when the input voltage is slightly higher, reducing power dissipation and eliminating the need for expensive inductive components, while maintaining adequate voltage regulation and minimizing noise injection during startup and steady-state operations.
Implementation Method 1
using a depletion mode n-channel field effect transistor and a voltage detector circuit to control charging current
Implementation Method 2
A bridge rectifier converts an AC input voltage from a source into a rectified signal
Implementation Method 3
The storage capacitor is coupled between an output voltage VO node and the GND node
Data Source
AI summary
In a steady state operation mode, a charging circuit of a non-isolated AC-to-DC converter decouples an output voltage VO node from a VR node when the rectifier output signal VR on the VR node is greater than a first predetermined voltage VP and, 2) supplies a charging current from the VR node and onto the VO node when VR is less than VP provided that an output voltage VO on the VO node is less than a second predetermined voltage VO(MAX) and provided that VR is greater than VO. In an initial power up operation mode, the maximum limit value of the charging current is smaller than it is during steady state operation. Due to the reduced charging currents employed during initial power up operation, less noise is injected back to the AC source and EMI filters are not required between the rectifier of the converter and the AC source.