Power Supply Controller PWM Signal Generation
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Solution Overview
Problem
Existing power supply controllers for semiconductor switching elements face challenges in generating a PWM signal with high accuracy due to manufacturing variations and voltage fluctuations, leading to inconsistent oscillating frequencies and duty ratios, which can cause flickering in vehicle headlamps during daytime driving.
Innovation Solution
A power supply controller with a PWM signal generator that includes an oscillator circuit, comparator circuit, and a parallel circuit with external resistive elements and capacitors, allowing for precise control of oscillating frequency and duty ratio, immune to manufacturing variations and voltage fluctuations, and capable of operating without a microcomputer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an oscillator circuit is provided in the semiconductor device, then the device can generate PWM signals, but the oscillating frequency varies due to manufacturing variations of capacitor and resistor elements
Solution Approach 1:
The patent changes the operating parameters of the oscillator circuit by introducing a power supply voltage detection circuit that dynamically adjusts the oscillation frequency based on the detected voltage level. When voltage fluctuations are detected, the circuit modifies the charging/discharging current of the capacitor through control signals, thereby maintaining a stable oscillating frequency despite variations in power supply voltage or manufacturing tolerances of passive components.
2Ease of operation
If threshold voltages are set using a voltage-dividing circuit in the semiconductor device, then the circuit can compare oscillator signal levels, but the thresholds vary due to manufacturing variations
Solution Approach 1:
The patent implements a feedback mechanism where the power supply voltage detection circuit continuously monitors the voltage level and feeds back control signals to both the oscillator circuit and the threshold setting circuit. This feedback loop dynamically adjusts the threshold voltages to maintain accurate duty ratio control, compensating for manufacturing variations in the voltage-dividing circuit elements and ensuring precise PWM output despite component tolerances.
3Adaptability or versatility
If the power supply voltage fluctuates, then the vehicle can operate during engine start, but the thresholds of the hysteresis comparator fluctuate causing duty ratio variation
Solution Approach 1:
The patent applies preliminary action by detecting power supply voltage fluctuations before they significantly affect the PWM output. The power supply voltage detection circuit monitors voltage changes in advance and proactively adjusts the oscillator frequency and threshold levels through control signals. This preemptive adjustment prevents duty ratio variation caused by voltage fluctuations during critical operations such as engine starting.
4Illumination intensity
If the oscillating frequency is set low to reduce flickering, then visibility is improved, but the frequency may drop below the threshold causing visible flicker
Solution Approach 1:
The patent transforms the static oscillating frequency into a dynamic parameter that can be adjusted in real-time. The power supply voltage detection circuit continuously monitors operating conditions and dynamically modifies the oscillation frequency through control signals that adjust the capacitor charging/discharging current. This dynamic adjustment ensures the frequency remains above the flicker threshold (e.g., 40 Hz) under all operating conditions while allowing for lower frequencies when stable operation is achieved, thus preventing visible flicker and ensuring consistent headlamp visibility.
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
The solution enables the generation of a PWM signal with high accuracy and stability, ensuring consistent headlamp operation by adjusting the oscillating frequency and duty ratio, effectively suppressing the effects of manufacturing variations and voltage fluctuations, thus preventing flickering.
Implementation Method 1
The parallel circuit includes a first resistive element and a capacitor, which are arranged parallel to each other
Implementation Method 2
based on the interterminal voltage of a capacitor that repeats charge and discharge, a triangular wave signal is provided
Implementation Method 3
The hysteresis comparator compares in magnitude the level of the triangular wave signal with two threshold voltages provided therein, and outputs an output signal as a PWM signal according to level inversion of the magnitude relation
Data Source
AI summary
A parallel circuit 27 of a frequency control circuit 11 is provided as an external circuit. Thereby, the charging time t1 depends on the characteristics of the circuit elements, which are provided in the package of a semiconductor device 70 and therefore subject to manufacturing variations of the semiconductor device 70. The discharging time t2 depends on the parallel circuit 27, which is provided external to the semiconductor device 70 and therefore can be selected to have appropriate characteristics after the semiconductor device 70 has been manufactured. The circuit constants of circuits are set so that the discharging time t2 that depends on the device characteristics of the external parallel circuit 27 is longer than the charging time t1 that depends on the device characteristics of the internal circuits of the semiconductor device 70.