Power Supply Control Circuit for Inrush Current Management
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Solution Overview
Problem
Image forming apparatuses with electrophotographic processes face challenges in controlling power supply voltage when abnormal currents are generated due to short circuits or other malfunctions, leading to inrush currents that can exceed safe limits and cause damage.
Innovation Solution
Incorporating a power supply control circuit with a field-effect transistor (FET) and resistive and capacitative elements in series, which prevents immediate potential difference and current flow, allowing for gradual switching and reducing inrush currents, and includes a detector and controller to manage drive voltage fluctuations and flag generation for error detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switch is provided on the power supply path to cut off power when the cover is opened, then power supply safety is improved, but high inrush current flows into the condenser when the switch closes again, exceeding the upper limit
Solution Approach 1:
The patent introduces an intermediary circuit between the switch and the condenser consisting of a diode and a resistor. The diode prevents reverse current flow, while the resistor limits the inrush current when the switch closes, protecting both the switch and condenser from damage.
Solution Approach 2:
The patent applies beforehand cushioning by pre-configuring protective elements (diode and resistor) in the power supply circuit before any inrush current can occur. These elements are always in place to cushion or limit the inrush current when the switch closes, preventing damage without requiring active control.
2Object-generated harmful factors
If electronic switches such as FETs are provided on the power supply path to divide power supply destinations and turn them on sequentially, then inrush current control is improved, but the capability to control power supply voltage in case of abnormal current is insufficient
Solution Approach 1:
The patent implements feedback by monitoring the voltage at specific nodes in the power supply circuit and using this information to control the switching of FETs. When abnormal conditions are detected through voltage monitoring, the system adjusts FET switching to protect the circuit, thereby improving both inrush current control and abnormal current handling capability.
3Reliability
If the switch and FETs are opened to cut off power when the cover is opened, then power supply safety is improved, but abnormal current may still flow into optional devices if a short circuit occurs due to inappropriate mounting
Solution Approach 1:
The patent applies segmentation by dividing the power supply circuit into multiple independently controllable segments using FETs. Each optional device or circuit section has its own FET control, allowing the system to isolate and cut off power to specific segments where short circuits or abnormal conditions occur, while maintaining power supply to other safe segments.
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 configuration effectively prevents excessive inrush currents, allows for controlled power supply, and enables accurate detection and notification of errors, ensuring safe operation and reducing the risk of component damage.
Implementation Method 1
a field-effect transistor with its source connected to the power source side of the power supply path, and its drain connected to the second drive unit side of the power supply path
Implementation Method 2
a second resistive element and a capacitative element that are connected in parallel with the first resistive element, and connected with each other in series between the gate and the source
Data Source
AI summary
An image forming apparatus for forming an image with an electrophotographic process, that includes: a power source; a first drive unit having a capacitative load and driving each part of the apparatus; a second drive unit having a capacitative load and driving each part of the apparatus; and a power supply control circuit that is provided on a power supply path between the power source and the second drive unit, that switches whether or not electric power is supplied to the second drive unit. The power supply control circuit includes: a field-effect transistor with its source connected to the power source side of the power supply path, and its drain connected to the second drive unit side of the power supply path; a first resistive element connected between the field-effect transistor's gate and its source; a second resistive element and a capacitative element that are connected in parallel with the first resistive element, and connected with each other in series between the gate and the source.