Primary-Side Adaptive Digital Controller for BJT Flyback Converter
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Solution Overview
Problem
Conventional controller ICs for primary-side feedback switching power converters require an additional pin and ADC circuitry to sense the input line voltage, increasing die size and manufacturing cost, and face challenges in designing efficient driver circuits for BJT switches.
Innovation Solution
A controller for an AC/DC flyback switching power converter uses adaptive digital control to regulate secondary-side output voltage and current based on primary-side feedback, eliminating the need for an input line voltage sensing pin and ADC circuitry by controlling switching cycles based on sensed primary-side current, and dynamically adjusting BJT base current amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional controller ICs use input line voltage sensing with separate pin and ADC circuitry, then output voltage regulation is achieved, but die size and manufacturing cost increase
Solution Approach 1:
The patent removes the separate input line voltage sensing pin and ADC circuitry from the controller IC, extracting these functions entirely. Instead, the controller uses primary-side current sensing through existing circuitry to achieve output voltage regulation without the additional components that would increase die size.
Solution Approach 2:
The controller IC is designed to perform multiple functions using the same circuitry. The primary-side current sensing circuitry serves dual purposes: it controls the switching operation and provides the basis for output voltage regulation, eliminating the need for dedicated voltage sensing components.
2Measurement precision
If conventional controller ICs use input line voltage sensing with separate pin and ADC circuitry, then output voltage regulation is achieved, but manufacturing cost increases
Solution Approach 1:
The patent removes the separate input line voltage sensing pin and ADC circuitry from the controller IC, extracting these functions entirely. Instead, the controller uses primary-side current sensing through existing circuitry to achieve output voltage regulation without the additional components that would increase die size.
Solution Approach 2:
The patent employs simpler, less expensive circuitry for voltage regulation by using the existing primary-side current sensing capability rather than investing in expensive ADC circuitry and separate sensing pins, reducing overall manufacturing cost.
3Ease of manufacture
If BJT is used as power switch, then cost is reduced and EMI noise is minimized, but driver design becomes more challenging
Solution Approach 1:
The BJT driver circuit is designed to automatically adjust its operation based on the switching conditions without requiring complex external control. The driver monitors the primary-side current and autonomously regulates the base current amplitude, making the driver design simpler while maintaining BJT cost advantages.
4Area of stationary object
If primary-side feedback control without line voltage sensing is used, then die size and cost are reduced, but control precision must be maintained
Solution Approach 1:
The patent implements a feedback control mechanism that monitors the primary-side current and uses this information to regulate the secondary-side output voltage and current. The controller adjusts the switching duty cycle based on feedback from the output, maintaining precise regulation without needing direct input voltage sensing.
Solution Approach 2:
The controller dynamically changes the switching parameters (duty cycle, frequency) based on the primary-side current measurements and feedback from the output, enabling precise voltage and current regulation through adaptive parameter adjustment rather than direct voltage sensing.
Data Source
AI summary
A controller of an AC/DC flyback switching power supply uses adaptive digital control approaches to control the switching operation of a BJT power switch based on primary-side feedback to regulate the secondary-side constant output voltage and output current, without using the input line voltage. Switching-cycle by switching-cycle peak current control and limit are achieved based on the sensed primary-side current rather than the input line voltage in both constant-voltage and constant-current modes, operating in PWM, PFM and/or combinations of a plurality of PWM and PFM modes. The controller IC does not need a separate pin and ADC circuitry for sensing the input line voltage. The controller IC directly drives the BJT base, and dynamically adjusts the BJT base current amplitude cycle by cycle based on load change.