PWM Signal Generation Circuit for Temperature-Stable LED Dimming
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Solution Overview
Problem
Existing PWM signal generation circuits face challenges in maintaining a constant duty ratio and linear characteristics, as they are affected by temperature changes and nonlinearity in discharge voltage, making it difficult to control the brightness of LEDs and other applications reliably.
Innovation Solution
A PWM signal generation circuit comprising a counting circuit, pulse period control circuit, pulse width control circuit, and control logic circuit that generates a PWM signal by converting counting signals into analog outputs and comparing them with reference voltages to determine the period and pulse width, ensuring a constant duty ratio despite temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a general PWM signal generation circuit uses resistors and capacitors outside the chip to generate PWM signals by changing charge and discharge time, then the circuit can generate PWM signals, but the duty ratio becomes difficult to maintain constant due to temperature changes and nonlinearity in discharge voltage
Solution Approach 1:
The patent replaces the traditional RC-based PWM generation method with a Delta-Sigma modulation-based digital circuit implementation. The counting circuit generates a triangle wave by counting clock signals, and the comparison circuit compares this with a reference voltage to generate PWM signals. This digital approach eliminates the temperature-sensitive RC components while maintaining PWM functionality, thereby resolving the contradiction between generating PWM signals and maintaining duty ratio stability under temperature variations.
2Manufacturing precision
If a charged capacitor is discharged using a resistor, then the discharge process can be controlled, but it is difficult to secure linear characteristics and the resistor or capacitor affects the duty according to temperature changes
Solution Approach 1:
The patent substitutes the analog RC discharge mechanism with a digital counting and comparison mechanism. The counting circuit generates a linearly increasing voltage representation through digital counting, and the comparison circuit performs precise voltage comparison to generate PWM signals. This digital approach ensures linear discharge characteristics independent of temperature, resolving the contradiction between controlling discharge and maintaining linearity under temperature variations.
3Measurement precision
If PWM signals are generated by varying pulse width to control average voltage, then the amplitude of analog output can be controlled, but the duty ratio varies with temperature affecting control precision
Solution Approach 1:
The patent implements a digital Delta-Sigma modulation circuit that generates PWM signals through counting and comparison operations rather than analog RC timing. The counting circuit produces a linear ramp signal by counting clock cycles, and the comparison circuit compares this ramp signal with a reference voltage to determine PWM duty cycle. This digital implementation ensures precise and temperature-independent duty ratio control, resolving the contradiction between control precision and duty ratio constancy.
Data Source
AI summary
Disclosed are a pulse width modulation (PWM) signal generation circuit and a lamp control system including the same. The PWM signal generation circuit includes a counting circuit configured to generate a counting signal, a pulse period control circuit configured to convert the counting signal into a first analog output signal and compare the first analog output signal with a first comparison voltage to generate a first output signal, a pulse width control circuit configured to convert the counting signal into a second analog output signal and to compare the second analog output signal with a second comparison voltage to generate a second output signal, and a control logic circuit configured to determine a period of a PWM signal based on the first output signal, determine a pulse width of the PWM signal based on the second output signal, and output the PWM signal having the period and the pulse width.