Chopper Circuit Switching Frequency Control for Noise Reduction
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Solution Overview
Problem
Conventional image forming apparatuses experience issues with recovery noise in the freewheeling element and temperature rise in the switching element due to continuous current mode operation during high duty cycles, leading to inefficiencies and noise generation.
Innovation Solution
An image forming apparatus with a chopper circuit that includes a reactor, freewheeling element, and switching element, where the control part adjusts the duty cycle and switching frequency based on temperature and current detection, switching to discontinuous current mode when the duty cycle exceeds a reference value and setting the frequency outside the audible range to prevent noise and temperature rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the chopper circuit operates in continuous current mode during high duty cycle, then the heater can be efficiently powered, but recovery noise is generated in the freewheeling element and temperature rise occurs in the switching element
Solution Approach 1:
The patent dynamically switches between continuous current mode and discontinuous current mode based on the duty cycle. When the duty cycle exceeds a threshold, the system transitions to discontinuous current mode, making the operating state adaptive rather than fixed, thereby resolving the contradiction between efficiency and harmful effects
Solution Approach 2:
The patent changes the current mode parameter from continuous to discontinuous when the duty cycle exceeds a threshold value. This parameter change eliminates recovery noise in the freewheeling element and prevents temperature rise in the switching element while maintaining adequate heater power delivery
2Measurement precision
If the switching frequency is set high to improve PWM control precision, then the duty cycle control becomes more accurate, but the switching element experiences increased temperature rise due to switching loss
Solution Approach 1:
The patent changes the current mode parameter from continuous to discontinuous when the duty cycle exceeds a threshold value. This parameter change eliminates recovery noise in the freewheeling element and prevents temperature rise in the switching element while maintaining adequate heater power delivery
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 effectively prevents recovery noise in the freewheeling element and temperature rise in the switching element, while maintaining efficient power supply to the heater, reducing sound noise and improving operational stability.
Implementation Method 1
a chopper circuit having a reactor, a freewheeling element, and a switching element, the chopper circuit being configured to switch an input direct current on and off in a specified duty cycle by using the switching element and to supply the current to the heater
Implementation Method 2
a chopper circuit having a reactor, a freewheeling element, and a switching element, the chopper circuit being configured to switch an input direct current on and off in a specified duty cycle by using the switching element and to supply the current to the heater
Implementation Method 3
a fixing part having a heater
Data Source
AI summary
An image forming apparatus includes: a fixing part including a heater, and a first temperature detection part configured to detect the temperature of the heater; a chopper circuit including a reactor, a freewheeling element, and a switching element, the chopper circuit being configured to switch an input direct current on and off in a specified duty cycle by using the switching element and to supply the current to the heater; and a control part configured to control the duty cycle based on a detection result obtained by the first temperature detection part, as well as to control a switching frequency of the switching element based on an operation mode of the image forming apparatus.