Startup Circuit Schmitt Triggers Power Dissipation
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Solution Overview
Problem
Power converters, such as adapters, face significant power dissipation issues during startup due to high startup currents, which lead to substantial no-load and low-load power losses, hindering efficiency improvements despite industry efforts to reduce these losses.
Innovation Solution
A startup circuit with a charge accumulation circuit and two Schmitt triggers is introduced, where the first Schmitt trigger draws a low bias current and latches on to start the second Schmitt trigger, providing a bias voltage for the controller, allowing the startup circuit to operate with minimal current draw and eliminating the need for a high-voltage switch, thereby reducing power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional startup circuit with high voltage switch is used, then the startup current can be switched off after startup, but the high voltage switch is relatively expensive and increases device complexity
Solution Approach 1:
The patent extracts and eliminates the high voltage switch from the traditional startup circuit. By removing this expensive and complex component, the invention achieves cost reduction and simplified circuit design while maintaining the ability to switch off startup current through an alternative mechanism using the controller's internal power switch.
Solution Approach 2:
The patent makes the controller's power switch serve dual functions: it acts as both the main power switch for the power converter and as the startup current switch. This multi-functionality eliminates the need for a separate high voltage switch, reducing component count and device complexity while achieving the same startup current switching capability.
2Reliability
If startup current is not switched off after startup, then the power converter can start up properly, but the no-load input power increases significantly
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors the startup process and uses its internal power switch to disconnect the startup current path after successful startup. This feedback-controlled switching ensures that the startup current is automatically turned off, eliminating continuous power dissipation while maintaining reliable startup operation.
Solution Approach 2:
The controller serves itself by using its own internal power switch to switch off the startup current, eliminating the need for external high voltage switches. The controller autonomously manages the startup current termination, achieving both reliability and energy efficiency without additional complex components.
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 power dissipation during startup, allowing the power converter to operate efficiently at low load levels without compromising performance, and can be adapted for high-volume manufacturing.
Implementation Method 1
a charge accumulation circuit having a resistor series-coupled to a capacitor and a first Schmitt trigger having an input coupled to the capacitor
Data Source
AI summary
A startup circuit with reduced power dissipation, method of operating the same and a power converter employing the startup circuit. In one embodiment, the startup circuit for a controller includes a charge accumulation circuit having a resistor series-coupled to a capacitor and a first Schmitt trigger having an input coupled to the capacitor. The startup circuit also includes a second Schmitt trigger having an input coupled to an output of the first Schmitt trigger and configured to provide a bias voltage for the controller via the capacitor when an input voltage thereto exceeds a trip voltage.