DC Power Supply Voltage Suppression for Light Load Overvoltage
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Solution Overview
Problem
In direct-current power supply devices with shared switching elements for PFC and DC/DC converters, the terminal voltage of the smoothing capacitor rises when the load is light, leading to potential overvoltage issues and increased costs due to the need for higher voltage-rated capacitors or additional protection circuits.
Innovation Solution
The implementation of a direct-current power supply device with voltage suppression means, including a discharging circuit that supplies the electric charge of the primary-side smoothing capacitor to the control circuit and electromagnetic energy from the reactor to the control circuit, to prevent voltage rises when the load is light, using additional switching elements and resistances to control the switching elements and manage energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the switching element is shared between PFC circuit and DC/DC converter, then device size is reduced and cost is lowered, but terminal voltage of smoothing capacitor rises when load is light
Solution Approach 1:
A third switching element is introduced as an intermediary component to control the discharge path of the smoothing capacitor. This additional switching element acts as a mediator between the smoothing capacitor and the rest of the circuit, enabling precise control of voltage discharge during light-load conditions without affecting the shared switching element's primary functions in PFC and DC/DC conversion.
Solution Approach 2:
The invention dynamically changes the operating parameters of the smoothing capacitor by controlling its discharge path through the third switching element. During light-load conditions, the switching element is activated to adjust the capacitor's voltage discharge rate, thereby maintaining stable terminal voltage. This parameter control approach allows the system to adapt to varying load conditions while preserving the benefits of shared switching elements.
2Reliability
If capacitor with higher voltage rating is used, then overvoltage protection is improved, but cost increases
Solution Approach 1:
The system provides self-service overvoltage protection through active control of the smoothing capacitor's discharge path. Instead of relying on passive components like higher voltage-rated capacitors or surge protectors, the invention uses the third switching element to actively regulate voltage, allowing the use of standard voltage-rated capacitors while maintaining protection against overvoltage conditions.
Solution Approach 2:
The control circuit monitors the terminal voltage of the smoothing capacitor and provides feedback control for the third switching element. When light-load conditions cause voltage to rise, the feedback mechanism activates the switching element to discharge the capacitor, thereby maintaining voltage within safe operating limits. This closed-loop control replaces the need for expensive high-voltage-rated capacitors.
3Reliability
If overvoltage protection circuit is added, then capacitor protection is improved, but device complexity and cost increase
Solution Approach 1:
The third switching element serves multiple functions: it controls the discharge path of the smoothing capacitor during light-load conditions, provides overvoltage protection, and works in coordination with the shared switching elements. This multi-functional approach integrates protection capabilities into the existing power conversion architecture without adding separate dedicated protection circuits, thereby minimizing additional complexity.
Solution Approach 2:
The invention merges the overvoltage protection function with the existing power conversion circuitry by utilizing the third switching element as part of the overall control scheme. Rather than adding a separate protection circuit, the discharge control is integrated into the same control system that manages the shared switching elements, combining multiple functions into a unified control architecture.
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 stabilizes the voltage of the smoothing capacitor, allowing for the use of capacitors with lower voltage ratings, reducing costs and improving reliability by preventing overvoltage and enhancing the efficiency of the power supply device.
Implementation Method 1
a discharging circuit that supplies electric charge of the primary-side smoothing capacitor to a power supply of a control circuit
Implementation Method 2
electromagnetic energy from the reactor to the control circuit
Data Source
AI summary
In a direct-current power supply device that includes a smoothing capacitor C1, which performs a DC/DC converter operation, a transformer T1, a switching element Q1, a diode D2, a smoothing capacitor C2, a reactor L1, which performs a PFC operation, a fast recovery diode D1 and a switching element Q1, when compared with the case of a rated load, the voltage of the smoothing capacitor C1 of a PFC circuit rises at a time when a load is light. Therefore, the following has been required: a capacitor having a sufficient withstanding voltage rating, or an operation of connecting a plurality of capacitors in series or any other operation to secure a voltage-withstanding capability.A direct-current power supply device 1, in which a switching element Q1 used by a PFC circuit is shared as a switching element Q1 by a DC/DC converter, includes voltage suppression means (switching elements Q2 and Q3 and resistance R2) for supplying electric charge accumulated in a smoothing capacitor C1 to a power supply Vcc of a control circuit CTL1 that controls the switching element Q1 at a time when a load is light in order to suppress a rise in voltage in the smoothing capacitor C1.