Self-Powered Source Driving Circuit for Switching Power Supplies
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Solution Overview
Problem
In switching power supplies, it is challenging to ensure that the power supply capacitor is charged to a sufficient voltage to supply the control circuit, especially when the input voltage is low, leading to potential power failures due to insufficient voltage for the control circuit, and adding extra capacitors increases energy consumption and switching losses.
Innovation Solution
A source driving circuit that includes a source transistor controlled by a PWM signal, a main power transistor that turns on when the gate-source voltage exceeds a conduction threshold, a source diode connected to a delay circuit and a power supply capacitor, where the delay circuit controls the main power transistor to turn off after a delay, allowing sufficient time for the power supply capacitor to be charged to a reference voltage level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power supply capacitor is charged to sufficient voltage using conventional methods, then the control circuit can operate reliably, but additional capacitors increase energy consumption and switching losses
Solution Approach 1:
The main power transistor's parasitic capacitance is utilized to charge the power supply capacitor for the control circuit. The transistor's inherent capacitance serves the dual purpose of switching function and power supply charging, eliminating the need for separate charging capacitors and reducing overall energy consumption.
Solution Approach 2:
The patent recovers energy that would otherwise be lost during the switching off-phase by utilizing the discharge current of the main power transistor's parasitic capacitance to charge the power supply capacitor. This converts what was previously wasted energy into useful charging current.
2Speed
If the main power transistor is turned off immediately after the source transistor, then switching speed is improved, but the power supply capacitor does not have sufficient time to charge
Solution Approach 1:
The power supply capacitor is charged during the off-phase of the source transistor before the main power transistor turns off. This preliminary charging action ensures that the control circuit has sufficient power supply voltage ready before the next switching cycle begins, maintaining both speed and reliability.
Solution Approach 2:
The charging of the power supply capacitor occurs continuously during the off-phase through the parasitic capacitance discharge, ensuring uninterrupted power supply preparation. This continuous useful action maintains power supply voltage sufficiency without delaying the switching cycle.
3Reliability
If extra capacitors are added to ensure sufficient charging voltage, then power supply reliability is improved, but device complexity and energy consumption increase
Solution Approach 1:
The main power transistor's parasitic capacitance performs multiple functions: it enables the switching action of the transistor and simultaneously serves as the charging source for the power supply capacitor. This multi-functionality eliminates the need for separate charging capacitors, reducing device complexity while maintaining power supply reliability.
Solution Approach 2:
The circuit uses its own inherent components (parasitic capacitance of the main power transistor) to charge the power supply capacitor, rather than requiring external or additional dedicated charging components. This self-service approach simplifies the overall circuit structure.
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 that the power supply capacitor is fully charged to provide a stable voltage for the control circuit without the need for additional capacitors, reducing energy consumption and switching losses while preventing power failures.
Implementation Method 1
a power supply capacitor, where a voltage across the power supply capacitor is configured to be charged to a reference voltage
Data Source
AI summary
In one embodiment, a source driving circuit configured for a switching power circuit, can include: (i) a source transistor coupled between a source of a main power transistor and ground, where the source transistor can be controlled by a PWM control signal; (ii) the main power transistor being on when the source transistor is on and a gate-source voltage of the main power transistor exceeds a conduction threshold voltage; (iii) a source diode having an anode coupled to the main power transistor source, and a cathode coupled to a delay circuit and a power supply capacitor; and (iv) the delay circuit controlling the main power transistor to turn off a delay time after the source transistor is turned off, where the delay time allows charging of the power supply capacitor such that a voltage across the power supply capacitor is at least a level of a reference voltage.