AC-DC Converter Discharge Circuit for Residual Charge Safety
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Solution Overview
Problem
Existing AC-DC converters face challenges in reducing size and cost while effectively addressing electric shock risks during AC power shutoff, as they require high-voltage elements for discharging and fail to manage residual charges in smoothing capacitors, leading to increased component count and power consumption.
Innovation Solution
The converter design includes a rectifier, an across-the-line capacitor, a smoothing capacitor, an AC shutoff detection circuit, and a discharging circuit with a junction transistor and discharging switch, allowing residual charges to be discharged without high-voltage elements, thereby reducing size and cost, and incorporating a diode and resistor for selective discharge targeting either the X capacitor or both capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a discharge resistor is provided in parallel with the X capacitor to discharge residual charges, then electric shock prevention is improved, but power consumption increases and device size increases
Solution Approach 1:
The patent applies dynamics by making the discharge resistor's connection state changeable - it is connected to the X capacitor during AC power interruption to discharge residual charges, and disconnected during normal operation to avoid continuous power consumption. This dynamic switching resolves the contradiction between electric shock prevention and power consumption.
Solution Approach 2:
The discharge resistor operates periodically rather than continuously - it is activated only during AC power interruption events to discharge the X capacitor, and remains inactive during normal AC power supply. This periodic action eliminates continuous power consumption while maintaining electric shock prevention capability when needed.
2Reliability
If high-voltage elements are used for discharging the X capacitor, then discharge effectiveness is improved, but device size and cost increase
Solution Approach 1:
The patent introduces a first switching element as an intermediary between the discharge resistor and the X capacitor. This switching element controls the connection and disconnection of the discharge resistor, enabling effective discharge when needed while avoiding the need for continuously connected high-voltage components, thus reducing device size.
Solution Approach 2:
The patent extracts the high-voltage discharge function from a continuously connected configuration to an on-demand configuration. By using a switching element to connect the discharge resistor only when AC power is interrupted, the system achieves effective discharge without permanently installing large high-voltage components, reducing overall device size.
3Reliability
If a control unit with many components is used to switch the discharge resistor, then discharge control is improved, but device complexity and cost increase
Solution Approach 1:
The first switching element serves multiple functions: it controls the discharge of the X capacitor by connecting/disconnecting the discharge resistor, and it is integrated into the existing power conversion circuitry. This multi-functionality reduces the need for separate control components, simplifying the overall device.
Solution Approach 2:
The patent merges the discharge control function with existing circuit elements - the discharge resistor is integrated into the power conversion circuit, and the first switching element is incorporated into the existing switching element of the power conversion circuitry, eliminating the need for a separate complex control unit.
4Reliability
If the discharge circuit is connected to high-voltage AC power supply, then discharge capability is improved, but element cost increases due to high-voltage requirements
Solution Approach 1:
The discharge circuit's voltage exposure is made dynamic - the discharge resistor is connected to the high-voltage X capacitor only briefly during AC power interruption for discharge purposes, then disconnected. This dynamic connection allows effective high-voltage discharge capability while using lower-cost components that don't need to continuously withstand high voltage.
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 enables efficient discharge of residual charges, reducing the risk of electric shocks and minimizing component count and power consumption, achieving size and cost reduction while ensuring safety and efficiency.
Implementation Method 1
a junction transistor which has a drain terminal connected to the first connection point and lowers discharge voltage that is voltage of the residual charges being discharged; and a first discharging switch which is connected to a source terminal of the junction transistor and allows the residual charges to be discharged, the source terminal being a terminal on a voltage drop side
Data Source
AI summary
A converter includes: a bridge diode; an X capacitor provided upstream of the bridge diode; a smoothing capacitor provided downstream of the bridge diode; an AC shutoff detection circuit which outputs an AC shutoff detection signal when input AC voltage is shut off; and a discharging circuit which is connected to a connection point at which the cathode of the bridge diode and the smoothing capacitor are connected, and allows residual charges in the smoothing capacitor and the X capacitor to be discharged when the AC shutoff detection signal is output, and the discharging circuit includes a JFET which has a drain terminal connected to the above connection point and lowers discharge voltage; and a first discharging switch element connected to the source terminal of the JFET.