Power Adapter Start-Up Circuit with Crowbar Discharge
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Solution Overview
Problem
Power adapters face significant no-load power losses due to high-voltage bus power draw and bleeder resistor currents, which are not effectively addressed by existing strategies, hindering further reduction of power dissipation while maintaining performance and manufacturability.
Innovation Solution
A start-up circuit and crowbar circuit are introduced in the power adapter to provide an initial bias voltage and quickly discharge capacitors when ac mains voltage is lost, reducing power consumption by disconnecting the power converter and using an active bleeder to minimize bleeder resistor losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bleeder resistor is used to discharge the X-capacitor upon loss of ac mains voltage, then safety is improved by rapidly reducing capacitor voltage, but no-load power loss increases due to continuous current flow through the resistor
Solution Approach 1:
The start-up circuit is pre-configured with a crowbar circuit that automatically activates upon detection of ac mains voltage loss. The circuit includes a capacitor charged during normal operation that triggers the crowbar switch to discharge the X-capacitor through a low-impedance path when voltage drops below a threshold, ensuring rapid discharge without continuous power consumption.
Solution Approach 2:
Instead of continuous discharge through a bleeder resistor, the invention uses periodic/cyclic action where the start-up circuit charges a capacitor during normal operation and then triggers a discrete discharge event through the crowbar circuit only when ac mains voltage is lost. This converts continuous power loss into a one-time energy dissipation event.
2Loss of energy
If the power converter is disconnected during no-load operation, then no-load power loss is reduced, but the controller cannot be properly powered during start-up conditions
Solution Approach 1:
The power adapter is segmented into distinct functional circuits: the main power converter that can be disconnected during no-load operation, and a separate start-up circuit that remains active to provide bias voltage and handle emergency discharge functions. This segmentation allows the controller to be powered only when necessary while minimizing overall power consumption.
Solution Approach 2:
The start-up circuit is designed to perform multiple functions: providing bias voltage to the controller during normal operation, discharging the X-capacitor upon ac mains voltage loss, and enabling the power converter to start up. This multi-functionality eliminates the need for separate dedicated circuits for each function, reducing overall component count and power loss.
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 significantly reduces no-load power losses in power adapters, achieving lower power consumption without compromising performance, and is adaptable to high-volume manufacturing techniques.
Implementation Method 1
a start-up circuit configured to provide an initial bias voltage for the power adapter
Implementation Method 2
The start-up circuit is configured to discharge a capacitor coupled across ac input terminals of the power adapter
Data Source
AI summary
A start-up circuit for a power adapter and method of operating the same. In one embodiment, the power adapter includes a start-up circuit configured to provide an initial bias voltage for the power adapter. The power adapter also includes a crowbar circuit configured to turn on the start-up circuit upon loss of an ac mains voltage supplied to the power adapter.