Switching Power Supply Zero-Cross Start With Capacitor Pre-Discharge
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Solution Overview
Problem
Existing power source devices with switching power sources experience significant noise generation when switching is started, especially when a filter with electrostatic capacity is used between the diode bridge and the switching portion.
Innovation Solution
A power source device that includes a rectifying portion, a switching portion, a detecting portion, a control portion, and a filter portion with a capacitor. The control portion executes a discharge operation to discharge the capacitor before starting the switching operation and synchronizes the switching start with the zero-cross point of the AC voltage, ensuring the electric power output during the discharge operation is less than during the switching operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a filter with electrostatic capacity is provided between the diode bridge and the switching portion to reduce switching noise, then switching noise is reduced, but the input voltage is clamped at maximum voltage during stop periods, causing significant noise when switching is started
Solution Approach 1:
The control portion executes a discharge operation before starting the switching operation from a stop state. This preliminary discharge action reduces the voltage across the capacitor from its clamped maximum value, ensuring that switching starts with a lower input voltage and thereby reducing starting noise while maintaining the noise reduction benefit of the filter during normal operation.
2Object-generated harmful factors
If the timing to start switching is synchronized with a zero-cross point to reduce noise, then switching noise is reduced, but significant noise is generated when switching is started due to high input voltage from the filter capacitor
Solution Approach 1:
The control portion performs a discharge operation before initiating the switching operation from a stop state. This preliminary discharge reduces the capacitor voltage, ensuring that even when switching starts at the zero-cross point, the input voltage is sufficiently low to minimize starting noise while preserving the zero-cross synchronization benefit.
Solution Approach 2:
The control portion dynamically adjusts the switching operation by executing a discharge operation before starting switching from a stop state. This dynamic control adapts the system state (capacitor voltage) based on operational conditions, ensuring low starting noise while maintaining effective noise reduction during normal switching operation.
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 solution effectively reduces noise when switching is started, even with a filter having electrostatic capacity, by controlling the switching operation to commence at a lower input voltage, thereby minimizing noise generation.
Implementation Method 1
a filter portion (130) including a capacitor, provided between the rectifying portion and the switching portion and configured to absorb a switching noise generated in the switching portion
Implementation Method 2
a rectifying portion configured to fully rectify an AC voltage
Data Source
AI summary
A power source device includes a rectifying portion, a switching portion to apply a voltage to a load, fully rectified by the rectifying portion, a detecting portion to detect a zero-cross point of the AC voltage, and a filter including a capacitor provided between the rectifying portion and the switching portion. A controller controls the switching portion so as to execute a discharge operation to discharge the capacitor before starting a switching operation from a stop state of the switching operation and so as to start the switching operation when the zero-cross point is detected by the detecting portion. An electric power outputted from the switching portion during the discharge operation is smaller than an electric power outputted from the switching portion during the switching operation.