Non-Isolated High Voltage DC-DC Feedback Using Floating Comparators
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Solution Overview
Problem
Conventional DC-DC converters with non-isolated input and output voltages face challenges in accurate output voltage regulation due to errors introduced by feedback components, such as diodes, which increase complexity and cost, and often require additional circuitry.
Innovation Solution
A non-isolated high voltage DC-DC converter design utilizing a pulse width modulator (PWM) circuit and power transistor with a feedback path featuring large resistive elements to generate high and low signals for comparator drivers, ensuring accurate output feedback voltage without interference from freewheeling diodes, and implementing a digital controller for efficient control logic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional feedback components (opto-coupler or transformer circuits) are used to feedback the DC-DC converter output voltage, then accurate output voltage regulation is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the feedback function from isolated components (opto-coupler/transformer) and implements it using simple resistive voltage division. The feedback path uses only resistors R1 and R2 to divide the output voltage, eliminating complex isolation components while maintaining regulation accuracy through direct voltage sampling.
Solution Approach 2:
The patent replaces expensive feedback components (opto-coupler or transformer circuits) with inexpensive resistive elements. The feedback path uses simple resistors that are much cheaper than isolation components, achieving the same voltage sampling function without the cost and complexity premium.
2Device complexity
If inexpensive feedback components are used, then device cost is reduced, but feedback error is introduced
Solution Approach 1:
The patent implements a direct feedback path using resistors R1 and R2 that continuously sample the output voltage and feed it back to the control circuit. This feedback mechanism allows the controller to accurately sense output voltage variations and adjust the PWM duty cycle accordingly, maintaining precision despite using simple resistive components.
Solution Approach 2:
The patent creates a direct voltage relationship between the output and feedback points through resistive division. The feedback voltage is directly proportional to the output voltage through the resistor ratio, establishing an equipotential relationship that eliminates measurement errors and ensures accurate voltage sensing without complex transformation.
3Measurement precision
If compensation diodes are added to correct for diode drop, then output voltage accuracy is improved, but device complexity and error increase
Solution Approach 1:
The patent extracts the feedback sampling point to a location that naturally eliminates the diode drop issue. By sampling the voltage after the freewheeling diode D1 (at the cathode terminal), the feedback path bypasses the diode voltage drop entirely, making compensation unnecessary and simplifying the circuit.
Solution Approach 2:
Instead of adding compensation diodes to correct for the voltage drop as conventional approaches do, the patent inverts the approach by positioning the feedback sampling point to exclude the diode drop from the measurement entirely. This reverse thinking eliminates the need for compensation components.
Data Source
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AI summary
A method and apparatus for regulating a non-isolated high voltage converter applies a PWM signal to a power transistor that couples an input voltage to a floating ground node to charge an inductor and generate an output voltage which is measured with a first floating comparator to disable the PWM signal upon detecting a high threshold output voltage, the first floating comparator having inputs connected across first and second resistive elements to measure a voltage across a feedback resistor connected in series with a diode between the output voltage and a neutral ground reference. Subsequently, the output voltage is measured with a second floating comparator to enable the PWM signal upon detecting a low threshold output voltage, where the second floating comparator has inputs connected across the first and second resistive elements to measure the feedback voltage across the feedback resistor.