LED Driver Circuit Using Segmented PWM for Ripple Reduction
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Solution Overview
Problem
Existing LED operating circuits face challenges in maintaining constant current and minimizing ripple, which affects the stability of the light spectrum, especially when controlling brightness using PWM methods, and require complex measurement circuits to achieve constant current.
Innovation Solution
A control/regulating unit adjusts the switch-on ratio and generates low-frequency PWM packets of adjustable width to regulate the LED current, using a sensor unit to monitor the current and adjust the switch-on time to maintain a nominal value, thereby reducing ripple and ensuring constant LED power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PWM method is used to control brightness, then brightness control flexibility is improved, but current ripple increases and light spectrum stability deteriorates
Solution Approach 1:
The patent segments the PWM control into two independent parts: low-frequency PWM packets for brightness control and high-frequency switching for current regulation. This segmentation allows brightness to be controlled flexibly while maintaining stable light spectrum through separate high-frequency current regulation that compensates for ripple effects.
Solution Approach 2:
The patent employs periodic high-frequency switching action within each low-frequency PWM packet to regulate current. This periodic action at high frequency creates a zigzag current pattern that maintains constant average current while allowing low-frequency PWM to control brightness, thus resolving the contradiction between brightness flexibility and spectrum stability.
2Measurement precision
If complex measurement circuits are used to achieve constant current, then current regulation precision is improved, but device complexity increases
Solution Approach 1:
The patent implements self-service current measurement where the control unit directly monitors the switching elements and coil current to infer LED current. This eliminates the need for separate complex measurement circuits while maintaining precise current regulation through the control unit's internal monitoring capabilities.
Solution Approach 2:
The patent uses the coil current and switching element states as intermediaries to indirectly measure LED current. Instead of directly measuring LED current with complex circuits, the control unit uses the easily measurable coil current and switching states as intermediaries to calculate and regulate LED current with high precision.
3Measurement precision
If high-frequency switching is used to regulate current, then current control precision is improved, but ripple effect increases and light spectrum changes
Solution Approach 1:
The patent implements feedback control where the control unit continuously monitors the actual current through the coil and switching elements, compares it with the target current, and adjusts the switching timing accordingly. This feedback mechanism maintains high current control precision while compensating for ripple effects and keeping the light spectrum stable despite high-frequency switching.
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 approach allows for flexible operation of LEDs with varying numbers connected, maintaining constant current and minimizing ripple, thus stabilizing the light spectrum and improving brightness control.
Implementation Method 1
a supply voltage for at least one LED is provided by means of a coil and a switch clocked by a control/regulating unit, with energy being temporarily stored in the coil when the switch is switched on, which is discharged via at least one LED when the switch is switched off
Data Source
Figure 1a~1b
Figure 2a~3a
Figure 3b~4
AI summary
Operating circuit for at least one LED, in which a supply voltage for at least one LED is provided by a clocked switch (S1), wherein when the switch (S1) is switched on, energy is buffer-stored in a coil (L1), which energy is discharged when the switch (S1) is switched off via at least one LED, and an open-loop/closed-loop control unit (SR) actuates the switch (S1) in such a way that the LED current (iLED) is regulated to a predetermined value and, in order to adjust the brightness of the LED, in each case low-frequency PWM packets of adjustable width are generated, characterized in that, during a low-frequency PWM packet, the switch-on time of the switch (S1) after a plurality of pulses of an adjustable switch-on time is altered to the next higher or lower adjustable switch-on time, and the remaining pulses are output with this altered switch-on time, with the result that the number of pulses with the two adjusted switch-on times assume a specific ratio and an averaged value for the current through the LED results, which value corresponds to the preset by a setpoint value and, in the event of a specific brightness value and therefore a specific width of the low-frequency PWM packet being undershot, individual pulses of the one adjusted switch-on time are omitted, and therefore the ratio of the number of pulses with the two adjusted switch-on times deviates in comparison with the operation with the same LED current during a low-frequency PWM packet with a greater width.