Flyback Voltage Supply Circuit Using N-MOSFET Load Switching
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Solution Overview
Problem
Existing voltage supply circuits for consumers like electronic ballasts and battery chargers are inefficient in handling higher voltages and require larger, more expensive p-channel MOSFETs due to high heat loss and space requirements, which is not practical for all country-specific voltage values and frequencies.
Innovation Solution
Assigning a flyback converter to generate a switching voltage higher than the supply voltage, using an n-channel MOSFET connected upstream to switch consumers on/off, with a snubber circuit to reduce voltage and prevent heat loss, and incorporating an interference suppression capacitor to manage electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a p-channel MOSFET is used to switch loads with rectified supply voltage, then the MOSFET can be directly controlled by the microcontroller, but the drain-source resistance is considerably higher resulting in high heat dissipation and larger device size
Solution Approach 1:
An N-MOSFET is introduced as an intermediary switching device between the microcontroller and the load. The N-MOSFET has lower on-resistance and better heat dissipation characteristics compared to P-MOSFET. A level shifter circuit acts as a mediator to translate the microcontroller's logic levels to the appropriate gate drive voltage for the N-MOSFET, enabling efficient switching while maintaining controllability.
Solution Approach 2:
The invention changes the type of MOSFET from P-channel to N-channel, fundamentally altering the electrical parameters. N-MOSFETs have lower threshold voltage, lower on-resistance, and better thermal characteristics. The level shifter circuit adjusts the gate-source voltage parameter to ensure proper switching operation with the N-MOSFET while maintaining compatibility with the microcontroller's output logic levels.
2Productivity
If a p-channel MOSFET is used with equivalent drain-source resistance to an n-channel MOSFET, then the switching performance is comparable, but the p-channel MOSFET takes up approximately four times the space
Solution Approach 1:
The invention uses a level shifter circuit, which is a simple and inexpensive component, to enable the use of N-MOSFETs. This approach is more cost-effective and space-efficient than using P-MOSFETs with equivalent performance. The level shifter adds minimal complexity while achieving the desired switching performance with significantly reduced component size.
3Loss of energy
If a flyback converter is assigned to generate switching voltage higher than supply voltage, then n-channel MOSFETs can be used for efficient switching, but additional voltage reduction circuitry is required
Solution Approach 1:
The flyback converter is designed to serve multiple functions: it provides isolated voltage generation, voltage step-up to create the necessary gate drive voltage for the N-MOSFET, and galvanic isolation between the high-voltage mains side and the low-voltage control side. This multi-functionality reduces the need for separate voltage conversion stages and simplifies the overall circuit 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
The solution allows for efficient, space-saving voltage supply and switching capabilities across various mains voltages and frequencies, reducing heat loss and costs by using n-channel MOSFETs, while effectively filtering out interfering voltages.
Implementation Method 1
a flyback converter, which generates a switching voltage higher than the supply voltage when a flyback converter transformer is switched
Implementation Method 2
this switching voltage is supplied via at least one N-MOSFET (n-channel metal oxide semiconductor field-effect transistor) connected upstream of a second load to switch it on/off
Implementation Method 3
with a snubber circuit to reduce voltage and prevent heat loss
Implementation Method 4
incorporating an interference suppression capacitor to manage electromagnetic interference
Data Source
Figure 1
AI summary
The invention relates to a voltage supply circuit for supplying at least two consumers, of which one consumer can be activated and deactivated, having a voltage connection for a mains voltage, downstream of which a filter device and a rectifier are arranged. Each consumer can be supplied with the rectified voltage via decoupling diodes and one flyback converter is associated with one consumer. Said flyback converter generates, by means of a switching device, particularly when switching a flyback converter transformer, a switching voltage higher than the supply voltage, wherein the switching voltage can be fed to the second consumer via at least one N-MOSFET for activating/deactivating. This creates a voltage supply circuit, which can be used not only for voltage supply at higher voltages, but also for switching, while having a simple and space-saving structure for corresponding consumers, in the form of electronic ballast units, control devices, battery chargers or the like.