Floating Output Boost Regulator Driving LEDs Using Buck Controller
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Solution Overview
Problem
Conventional boost converters for driving LEDs suffer from inefficiency and high input ripple when using a buck controller IC, leading to increased power losses and potential ripple issues in the power supply bus.
Innovation Solution
A buck type regulator configuration that creates a floating output boost regulator, where neither end of the LED string is connected to ground, allowing the anode end to be connected to the positive input voltage and the cathode end to a negative voltage generated by the converter, regulating only the current through the LEDs to achieve a boosted output voltage efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional positive-to-negative buck-boost converter topology is used with a buck controller IC, then the controller can provide desirable features, but the average current through the inductor and switches increases significantly, causing higher power losses
Solution Approach 1:
The patent inverts the conventional buck-boost topology by connecting the LED string between the positive input voltage and a generated negative voltage, rather than between ground and a positive output. This inversion changes the current path so that inductor current equals LED current, eliminating the additive current relationship that caused high power losses in the conventional topology
Solution Approach 2:
The patent changes the voltage reference parameters by creating a floating output where neither end of the LED string is grounded. The negative voltage terminal is generated relative to the positive input, transforming the electrical parameters to achieve lower current stress on power components while maintaining the desired LED driving capability
2Adaptability or versatility
If a conventional positive-to-negative buck-boost converter is used, then a buck controller IC can be utilized, but high input ripple is transferred to the output and high ripple appears on the power supply bus
Solution Approach 1:
By inverting the topology to connect LEDs between positive input and negative output, the patent reverses the ripple transfer direction. The series input inductor now isolates the power supply bus from switching ripple, and the floating output configuration prevents high ripple from appearing on the power supply bus, reducing EMI to levels comparable to traditional boost converters
Solution Approach 2:
The series input inductor acts as an intermediary element that blocks high-frequency switching ripple from propagating to the power supply bus. The floating output configuration serves as another intermediary, isolating the ripple-generating switching nodes from the input power source and reducing electromagnetic interference
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 configuration reduces power losses through the inductor and switches, maintains low input ripple, and allows for the use of existing buck controller ICs, improving safety margins and efficiency comparable to traditional boost converters while reducing EMI.
Implementation Method 1
When the switch 14 is on, an upward ramping current flows through the inductor L to charge the inductor L to a regulated peak current. After the peak current is reached, the switch 14 is turned off and the switch 12 is turned on. A downward ramping inductor current flows through the switch 12.
Implementation Method 2
The switch current is smoothed by the output capacitor Cout. The output capacitor Cout smooths the ripple in the inductor current IL provided to the output.
Data Source
AI summary
An LED driver uses a positive-to-floating boost converter topology to generate a negative voltage −Vee relative to ground. The converter receives an input voltage. Vin from a power supply. One end of an output inductor is coupled to ground, and the other end of the inductor is coupled between a highside switch and a low side switch. The bottom terminal of the lowside switch generates −Vee. The anode end of an LED string is coupled to Vin and the cathode end is coupled to −Vee. The converter detects the LED current and regulates the switching duty cycle so that the LED current is equal to a target current. This is more efficient than coupling the anode end of an LED string to ground and the cathode end to −Vee. A conventional buck controller IC may be used.