Self-Supply Circuit for Voltage Converter with Precharge Stage
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Solution Overview
Problem
Existing self-supply circuits for switched-mode voltage converters, particularly flyback type, face inefficiencies due to residual power dissipation through start-up resistors and limitations on duty cycle, which restrict the operation and efficiency of the converters, especially during battery-charging and high duty cycle conditions.
Innovation Solution
The introduction of a precharge stage connected directly to the gate terminal of the auxiliary transistor allows for rapid switching and precharging of the gate-source capacitance during the ON phase of the main transistor, enabling continuous charging of the accumulation capacitor without time delays and allowing higher duty cycles without efficiency loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a start-up resistor is used to supply initial power to the PWM controller, then the controller can be turned on, but residual current flows through the resistor during normal operation causing power dissipation and reduced efficiency
Solution Approach 1:
The patent extracts the start-up function from the continuous power supply path by using a dedicated start-up transistor that is turned off after the controller is initialized. This separates the startup requirement from the ongoing power consumption, eliminating residual current through the start-up resistor during normal operation and resolving the contradiction between reliable startup and energy efficiency.
Solution Approach 2:
The patent applies preliminary action by pre-charging the accumulation capacitor through the start-up transistor before normal operation begins. Once the capacitor is charged to the required voltage level, the start-up transistor is turned off, and the controller is supplied through the auxiliary winding during switching operations, avoiding continuous power loss.
2Adaptability or versatility
If the auxiliary winding is used to supply feedback for output current regulation, then both voltage and current can be regulated, but the voltage on the auxiliary winding may be insufficient to supply the PWM controller
Solution Approach 1:
The patent segments the power supply function into two distinct paths: a start-up path using the start-up transistor and accumulation capacitor for initial controller power, and a feedback path using the auxiliary winding for output regulation. This segmentation allows the auxiliary winding to be dedicated to feedback without needing to provide sufficient voltage for controller supply, resolving the contradiction between dual regulation capability and controller supply adequacy.
3Loss of energy
If the start-up transistor is switched off after startup, then power dissipation is reduced, but the accumulation capacitor must be continuously recharged during high duty cycle operation
Solution Approach 1:
The patent ensures continuity of useful action by maintaining the start-up transistor in the off state during normal operation, eliminating continuous power dissipation through the start-up resistor. The accumulation capacitor is charged during the off-time periods of the main switching transistor, and this charged capacitor continuously supplies the controller during high duty cycle operation, ensuring uninterrupted power without requiring the start-up transistor to remain on.
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 ensures uninterrupted self-supply to the PWM controller, maximizing the useful time for charging the accumulation capacitor and eliminating limitations on the duty cycle, thereby enhancing the overall efficiency and operational range of the voltage converter.
Implementation Method 1
an accumulation capacitor (16), connected between the supply terminal (13) and the reference terminal (9)
Implementation Method 2
a transformer (4), having a primary side and a secondary side, which is electrically isolated from the primary side
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Described herein is a self-supply circuit (30), for a voltage converter (1) that converts an input voltage (Vin) into an output voltage (Vout) and has a main switch (10) and a controller (12), designed to control switching of the main switch (10) for controlling the output voltage (Vout); the self-supply circuit (30) is provided with: a charge accumulator (16), which is connected to the controller (12) and supplies a self-supply voltage (Vcc) to the same controller; a generator (24), which supplies a charge current (Icharge) to the charge accumulator (16); and an auxiliary switch (21), which has a first conduction terminal in common with a respective conduction terminal of the main switch (10) and is operable so as to control transfer of the charge current (Icharge) to the charge accumulator (16). In particular, the self-supply circuit (30) is provided with a precharge stage (31), connected to the auxiliary switch (21), which carries out a precharging of an intrinsic capacitance of the auxiliary switch (21) before a turning-off transient of the main switch (10) ends.