Start-up Time Accelerator in Switching Regulators
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Solution Overview
Problem
Flyback converter start-up times are excessively long due to large RC time constants, which are necessary for low power consumption during standby mode, making them unsuitable for applications requiring start-up times under 100 milliseconds.
Innovation Solution
A start-up time accelerator uses an NPN bipolar power transistor as a current amplifier to rapidly increase the bias voltage to the switch controller, reducing the time to reach the turn-on threshold voltage by providing an amplified current path to the capacitor, and subsequently switches to an auxiliary winding for bias voltage supply once the threshold is reached.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If large resistance and capacitance values are used in the RC start-up circuit, then power consumption during standby mode is minimized, but start-up time becomes excessively long
Solution Approach 1:
The start-up circuit is segmented into two distinct phases: a first start-up phase using the RC circuit with large R and C values for low power consumption, and a second accelerated phase using a separate current source to rapidly charge the capacitor. This segmentation allows each phase to optimize for its specific function without compromising the other.
Solution Approach 2:
The capacitor is pre-charged to a threshold voltage during the first start-up phase using the low-power RC circuit. Once the threshold is reached, the second current source is activated to complete the charging process rapidly. This preliminary action allows the system to transition from low-power mode to high-speed mode at the optimal moment.
2Use of energy by moving object
If large capacitance value is used for capacitor 102, then power is supplied to switcher circuit 104 after turn-on threshold is reached, but start-up time increases due to large RC time constant
Solution Approach 1:
The charging current for capacitor 102 is made dynamic rather than static. During the initial phase, a small current flows through the RC circuit. Once the threshold voltage is reached, a second, larger current source is activated to rapidly complete the charging. This dynamic current profile reduces the effective time constant while maintaining the required capacitance value for power supply.
Solution Approach 2:
The system changes the charging parameter (current magnitude) based on the charging state of the capacitor. Initially, a small current is used to slowly charge the capacitor to the threshold voltage. After the threshold is reached, the current magnitude is increased to rapidly charge the capacitor to its full operating voltage, thereby reducing the overall start-up time while maintaining the large capacitance value needed for power supply.
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 approach significantly reduces the start-up time of the switching regulator by up to a factor of (1+β), allowing for faster establishment of the desired output voltage, while maintaining low power consumption during standby mode.
Implementation Method 1
A start-up time accelerator uses an NPN bipolar power transistor as a current amplifier to rapidly increase the bias voltage to the switch controller
Implementation Method 2
capacitor 102 supplies power to switcher circuit 104 at terminal VC after terminal VC reaches the turn-on threshold voltage
Implementation Method 3
when a voltage from an auxiliary winding of a transformer is large enough to provide the bias voltage for the switch controller
Data Source
AI summary
A start-up time accelerator is described for a switch controller that controls turning on or off a switch in a switching regulator. The start-up time accelerator uses the switch as a current amplifier and provides the amplified current to a capacitor using a current amplification path. In one example, the capacitor provides the bias voltage to a switch controller for the switch. Providing an amplified current to the capacitor accelerates the rate at which the bias voltage increases and reduces the time until the bias voltage reaches the turn-on threshold voltage of the switch controller. After the turn-on threshold voltage of the switch controller is reached, a second path is enabled for current to and from the capacitor and the capacitor provides the bias voltage to the switch controller until a voltage from an output voltage terminal is sufficiently high to provide the bias voltage for the switch controller through an auxiliary winding of a transformer.