Resonant Power Supply Shield Plate for Light Load Frequency Control
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Solution Overview
Problem
Resonant switching power supply devices experience an increase in switching frequency when the load is light due to oscillating voltages caused by stray capacitance and leakage inductance, leading to inefficient operation and potential downsizing issues, as existing noise reduction techniques do not effectively address these oscillations.
Innovation Solution
The implementation of an electrostatic shield plate between the primary and secondary windings of the transformer, connected to a terminal opposite to the current resonant capacitor, forms a parallel circuit with the leakage inductance and stray capacitance, reducing the oscillating voltage and thereby controlling the switching frequency to maintain a stable output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If electrostatic shield plate is connected to positive or negative side of power source, then common mode noise is reduced, but oscillating voltage remains and switching frequency increases at light loads
Solution Approach 1:
The electrostatic shield plate is connected to an intermediary point (terminal of reactor opposite to primary winding) rather than directly to power source terminals. This intermediary connection provides a reference potential that reduces oscillating voltage more effectively while still maintaining common mode noise reduction capability.
Solution Approach 2:
The connection point of the electrostatic shield plate is changed from power source terminals to the reactor terminal, which alters the electrical parameters and potential distribution in the circuit. This parameter change enables better suppression of oscillating voltage caused by stray capacitance and leakage inductance.
2Reliability
If switching frequency is increased to reduce output voltage rise, then output voltage stability is improved, but operation efficiency decreases and downsizing becomes difficult
Solution Approach 1:
The oscillating voltage caused by stray capacitance and leakage inductance, which was previously harmful and caused output voltage rise, is converted into a beneficial effect by connecting the electrostatic shield plate to the reactor terminal. This connection provides a discharge path for the oscillating energy, converting it into a controlled phenomenon that maintains output stability without requiring excessive switching frequency increases.
3Object-generated harmful factors
If electrostatic shield plate is connected to primary winding terminal, then noise current is reduced, but oscillating voltage from stray capacitance is not effectively suppressed
Solution Approach 1:
The reactor terminal serves as an intermediary connection point that provides benefits from both approaches: it maintains the noise current reduction effect of connecting to the primary winding side while also providing effective suppression of oscillating voltage through the reactor's inductive properties.
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 reduces the oscillating voltage and subsequent increase in switching frequency, enabling efficient operation and downsizing of resonant switching power supply devices even at light loads by minimizing energy accumulation in stray capacitance and reducing noise.
Implementation Method 1
an electrostatic shield plate between the primary winding and secondary winding of the transformer, the electrostatic shield plate being connected to a terminal of the primary winding of the transformer
Implementation Method 2
oscillating voltages caused by stray capacitance and leakage inductance
Implementation Method 3
a resonant circuit that is connected in parallel to one of the switching elements and consists of a primary winding of a transformer and a current resonant capacitor
Implementation Method 4
A resonant current flows through a primary-side inductance element of the transformer and the current resonant capacitor as the switching elements are turned on and off
Data Source
AI summary
Provided is a resonant switching power supply device that can reduce a common mode noise as well as an increase in frequency when a load is light.A resonant switching power supply device 1 equipped with a PFM control circuit 10 to control a switching frequency in such a way that an output voltage is brought to a desired value includes: a resonant circuit where a primary winding N1 of a transformer T2, a current resonant capacitor Cri and a reactor Lr are connected in series; rectifying circuits D1, D2 and Co that are connected to secondary windings N2 and N3 of the transformer T2 and obtain the output voltage Vo; and an electrostatic shield plate S1 disposed between the primary winding N1 and secondary windings N2 and N3 of the transformer T2. The reactor Lr is connected to one terminal of the primary winding N1 of the transformer T2 and the current resonant capacitor Cri is connected to the other terminal of the primary winding N1 of the transformer T2; and the electrostatic shield plate S1 is connected to a terminal of the reactor Lr that is situated at the side opposite to where the primary winding N1 of the transformer T2 is connected.