Power source control circuit
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Solution Overview
Problem
In power source circuits supplying electric power to loads like brushless DC motors, the activation of control units with induced voltage can lead to rush currents when the capacitor is not sufficiently charged, potentially damaging components, as the main relay may turn on before the capacitor is fully charged.
Innovation Solution
A power source circuit configuration that includes a rectifier circuit, a capacitor, a main relay, and a microcomputer, where the microcomputer controls the main relay to prevent power source line conduction if the capacitor voltage is below a predetermined value, using additional components like a voltage detector, current limiting resistance, and phase detection circuit to ensure safe charging and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the microcomputer is activated with induced voltage from the load, then the control function is enabled, but the main relay may turn on before the capacitor is sufficiently charged causing rush current
Solution Approach 1:
The system performs preliminary checking of capacitor voltage status before enabling the main relay. The microcomputer detects whether the capacitor voltage has reached a predetermined threshold level, and only allows the main relay to conduct after this preliminary condition is satisfied, preventing rush current before it can occur.
Solution Approach 2:
The microcomputer continuously monitors the capacitor voltage and uses this feedback information to control the main relay's conduction state. When the capacitor voltage is below the threshold, the microcomputer maintains the main relay in a non-conducting state, and only switches it to conducting when the voltage feedback indicates sufficient charging has occurred.
2Productivity
If the main relay conducts the power source line when the capacitor is not sufficiently charged, then power supply is enabled, but rush current flows damaging components
Solution Approach 1:
The system applies preliminary anti-action by detecting capacitor voltage status before the main relay can conduct. The microcomputer prevents the main relay from turning on during the critical period when capacitor voltage is insufficient, thereby counteracting the potential harmful effect of rush current before it can occur.
Solution Approach 2:
The microcomputer acts as an intermediary between the capacitor charging process and the main relay control. It mediates the timing relationship by monitoring capacitor voltage and only permitting the main relay to conduct when the intermediary condition (sufficient voltage) is met, thus preventing direct connection that would cause rush current.
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
Prevents rush currents by ensuring the capacitor is charged via the proper route before the main relay conducts the power source line, thereby protecting components and ensuring safe operation of the power source circuit and motor drive circuits.
Implementation Method 1
The rectifier circuit rectifies AC voltage of an AC power source
Implementation Method 2
The capacitor smooths the voltage rectified by the rectifier circuit
Implementation Method 3
a load like a brushless DC motor configured to generate induced voltage when rotated by external force
Data Source
AI summary
In order to restrain damage of a component due to rush current, a main relay in a power source circuit is not turned on and does not conduct a power source line even when a heat source microcomputer is activated with a capacitor not sufficiently charged. This configuration avoids start of charging the capacitor without current limitation, to restrain damage of the component due to rush current.