Switching Power Supply Timing Control Circuit
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Solution Overview
Problem
Existing switching power supply devices require auxiliary windings for generating turn-on timing and optocoupler current, making them susceptible to variations in threshold values, which affects the turn-on and turn-off timings of the switching transistor.
Innovation Solution
A switching power supply device that eliminates the need for auxiliary windings by using a control circuit with a turn-on period control circuit, turn-off period control circuit, and Set-Reset flip-flop (SRFF) circuit to generate timing signals based on optocoupler current, sense voltage, and load power signals, allowing independent control of turn-on and turn-off timings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If auxiliary windings are used to generate turn-on timing and optocoupler current, then the switching power supply device can operate, but the device becomes susceptible to variations in threshold values which affects turn-on and turn-off timings
Solution Approach 1:
The patent extracts the timing generation function from the auxiliary windings and transfers it to a control circuit. The control circuit generates turn-on and turn-off timing signals independently of the auxiliary windings, thereby eliminating the dependency on threshold value variations and improving timing stability while reducing structural complexity.
Solution Approach 2:
The control circuit acts as an intermediary between the power supply components and the timing control function. It receives signals from the auxiliary windings but processes and generates timing signals independently, mediating the relationship between the physical windings and the switching timing to eliminate threshold value sensitivity.
2Ease of manufacture
If auxiliary windings are used for timing generation, then the circuit can function, but the number of components and structural complexity increases
Solution Approach 1:
The control circuit is designed to perform multiple functions: it processes signals from the auxiliary windings, generates turn-on timing signals, generates turn-off timing signals, and controls the switching transistor. This multi-functionality consolidates what would otherwise require separate dedicated circuits, simplifying the overall structure and easing manufacturing.
3Manufacturing precision
If threshold value variations affect switching transistor timing, then the basic circuit operation is maintained, but precise timing control becomes difficult
Solution Approach 1:
The control circuit incorporates feedback mechanisms where it monitors the state of the switching transistor and adjusts the timing signals accordingly. This feedback loop compensates for threshold value variations, ensuring precise timing control regardless of component variations, thereby improving both manufacturing precision and reliability.
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 enables precise control of switching transistor timings, reducing the influence of threshold value variations and eliminating the need for auxiliary windings, while also managing turn-on and turn-off cycles to prevent audible noise in varying load conditions.
Implementation Method 1
when a current starts to flow from the DC voltage Vin to the first winding L11 connected to the switching transistor MN2, an induced electromotive force is generated in the windings L12, L13, and L14 of the transformer 50, and energy is accumulated in the transformer 50
Implementation Method 2
a current flows to the photodiode PD2 of the optocoupler 60 in accordance with the value of the output voltage, and the internal resistance of the phototransistor PT2 is determined in accordance with the amount of light emitted from the photodiode
Data Source
AI summary
A switching power supply device includes a switching transistor, a sense resistor connected to the switching transistor in series and on which a sense voltage generates when the switching transistor is turned on, a transformer including a first winding to which an input voltage is applied when the switching transistor is turned on and a second winding connected to a load, an optocoupler in which an optocoupler current is generated based on an output voltage on the second winding side, a load power detection circuit that generates a load power signal in accordance with a turn-on period of the switching transistor, a turn-on period control circuit, a turn-off period control circuit, and an SRFF circuit.