Electronic Endoscope Processor: LED Current Control for PWM Overcurrent
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Solution Overview
Problem
LEDs in electronic endoscope systems are prone to destruction due to high-frequency PWM signals, which cannot be stably controlled, leading to output current peaks exceeding the rated value.
Innovation Solution
A processor for electronic endoscope with a current control unit that generates output current with a duty ratio corresponding to a PWM control signal and a lower-voltage control signal, and includes a feedback circuit to stabilize the current, protecting the LEDs by limiting the duty ratio and using a low-pass filter to attenuate high-frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-frequency PWM signal is used for dimming control to achieve high shutter speed imaging, then image capture quality is improved, but LED reliability deteriorates due to output current peaks exceeding rated value
Solution Approach 1:
The patent implements a feedback circuit that detects the actual current flowing through the LED and compares it with the target current. The feedback signal is used to adjust the PWM duty ratio in real-time, ensuring that the LED current remains within safe limits even during high-frequency PWM operation. This closed-loop control prevents current peaks that would otherwise damage the LED while maintaining the required shutter speed performance.
Solution Approach 2:
The patent dynamically adjusts the PWM duty ratio based on the actual LED current feedback. Rather than using a fixed duty ratio, the system continuously modifies the duty cycle to compensate for variations in LED characteristics and operating conditions. This dynamic adjustment allows the system to maintain optimal performance at high shutter speeds while preventing harmful current peaks that would reduce LED reliability.
2Measurement precision
If PWM dimming control is implemented to achieve precise light intensity control, then illumination control precision is improved, but current stability deteriorates due to response delay in feedback system
Solution Approach 1:
The feedback circuit continuously monitors the actual LED current and provides real-time correction signals to the PWM controller. This closed-loop control compensates for the inherent response delay in the feedback system by actively adjusting the duty ratio based on the most current (pun intended) measured current level, thereby maintaining both precision and stability.
Solution Approach 2:
The patent introduces an intermediate current control stage between the PWM signal generator and the LED. This intermediate stage acts as a buffer that smooths out rapid duty ratio changes and provides more stable current delivery to the LED while still responding to PWM dimming commands. The intermediary circuit helps bridge the gap between the discrete PWM control and the continuous current requirement of the LED.
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 processor effectively protects LEDs from overcurrent by stabilizing the output current, preventing damage during high-frequency PWM dimming operations.
Implementation Method 1
a feedback circuit unit that feeds back a current flowing through each of the light-emitting elements to stabilize the output current generated by the current generation unit
Implementation Method 2
a low-pass filter circuit having a cutoff frequency corresponding to a frequency of the PWM control signal as a circuit that performs the filtering processing
Data Source
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Figure 2
Figure 3(a)~3(b)
AI summary
One aspect of the present invention provides a processor for electronic endoscope, the processor being used in an electronic endoscope including an image sensor that is configured to capture an image of a biological tissue, the processor including: a light source unit that synthesizes light beams to be emitted from a plurality of light emitting elements to generate illumination light toward the biological tissue; and a current control unit that controls a current to be applied to each of the light emitting elements in the light source unit. The current control unit includes a current generation unit that generates, as a current to be applied to each of the light emitting elements, an output current which has a duty ratio corresponding to a pulse width modulation control signal (PWM control signal) and has an amplitude corresponding to a lower-voltage control signal selected from a first control signal and a second control signal obtained by subjecting the PWM control signal to filter processing, and a feedback circuit unit that feeds back a current flowing through each of the light-emitting elements to stabilize the output current generated by the current generation unit.