DC/DC Converter Hysteresis Control for LED Current Regulation
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Solution Overview
Problem
Existing buck converter designs face challenges in maintaining accurate current regulation during voltage variations, particularly with fast and wide output voltage changes, and require additional components for common return and high accuracy current measurement, limiting their effectiveness in applications like LED lighting.
Innovation Solution
A hysteresis control strategy using two shunt resistors for load current measurement, allowing the switch to turn on when the load current falls below a low-set-point and turn off when it exceeds a high-set-point, enabling continuous conduction mode and direct measurement of peak current, which can sustain a 100% duty cycle and provide high accuracy in current regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single shunt resistor is used for current measurement, then the circuit complexity is reduced, but the measurement accuracy during voltage variations deteriorates
Solution Approach 1:
The current measurement function is segmented into two separate shunt resistors: one for detecting current during switch on-time and another for detecting current during switch off-time. This segmentation allows each resistor to be optimized for its specific measurement interval, improving overall measurement accuracy while maintaining manageable circuit complexity through dedicated measurement paths for different operational phases.
2Device complexity
If conventional current sensing is used, then the circuit is simpler, but the response speed to fast voltage variations deteriorates
Solution Approach 1:
The shunt resistors are positioned to enable immediate current detection at the moment of switching events. By having dedicated shunt resistors for both on-time and off-time periods, the system performs preliminary current measurement ready-to-trigger switching actions without delay, achieving fast response to voltage variations while keeping the overall circuit structure relatively simple.
3Measurement precision
If additional components are added for common return and high accuracy measurement, then the measurement accuracy improves, but the device complexity increases
Solution Approach 1:
The two shunt resistors serve multiple functions: they provide accurate current measurement during different switching phases, enable proper current regulation, and work with the existing buck converter topology without requiring separate dedicated measurement circuits. This multi-functionality approach improves measurement accuracy while minimizing the increase in device complexity by reusing existing structural elements.
Data Source
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AI summary
A converter for feeding a load (Ls) via an inductor (L) with a current (iL) having a controlled intensity, lying between a maximum level (SPH) and a minimum level (SPL), the converter (10) including: - a switch (Q1) switcheable on and off to permit or prevent, respectively, feeding of current towards said inductor (L) and said load (Ls), - a first current sensor (RSHH) sensitive to the current flowing through said switch (M) when said switch is on, - a second current sensor (RSHL) sensitive to the current flowing through said inductor (L) through a recirculating diode (D1) when said switch (M) is off, - comparator circuitry (B2, B5), to identify if the current intensity, detected by said first current sensor (RSHH) and by said second current sensor (RSHL), reaches said maximum level (SPH) and said minimum level (SPL), respectively, by generating respective logical signals (IN1, IN2), and - drive circuitry (B3, B4) for said switch (M) sensitive to said logical signals (IN1, IN2), and configured to turn off said switch (M) when the current intensity detected by said first sensor (RSHH) reaches said maximum level (SPH) and turning on said switch (M) when the current intensity detected by said second current sensor (RSHL) reaches said minimum level (SPL).