Switching Controller Current Sensing Resistor Elimination
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Solution Overview
Problem
Conventional power converters experience reduced efficiency under light-load conditions due to the inevitable power consumption caused by a current-sense resistor connected in series with the power switch.
Innovation Solution
A switching controller for power converters is designed without a current-sense resistor, utilizing a current-sense circuit, PWM circuit, comparators, and a delay circuit to generate a switching signal that limits the switching current, eliminating the need for a current-sense resistor and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current-sense resistor is connected in series with the power switch to generate a current-sense signal, then the switching current can be monitored and controlled, but power consumption increases and efficiency decreases under light-load conditions
Solution Approach 1:
The invention extracts the current-sensing function from the main power path by using a separate auxiliary winding on the transformer. This auxiliary winding generates a current-sense signal proportional to the switching current without requiring a series resistor in the main current path, thereby eliminating the power loss associated with the current-sense resistor while maintaining accurate current monitoring capability
Solution Approach 2:
The patent introduces an auxiliary winding as an intermediary element that couples the primary and secondary circuits magnetically. This auxiliary winding serves as a mediator to transfer current information from the primary side to the control circuit without direct electrical connection, avoiding the need for a power-consuming current-sense resistor in series with the power switch
2Reliability
If a current-sense resistor is used to monitor switching current, then current limiting can be achieved, but manufacturing cost increases due to additional components
Solution Approach 1:
The invention merges the current-sensing function with the transformer structure by incorporating an auxiliary winding directly into the transformer core. This integration eliminates the need for separate current-sense resistors and associated circuitry, reducing component count and simplifying manufacturing while maintaining current limiting capability through the magnetically coupled signal
3Reliability
If a current-sense resistor is connected in series with the power switch, then the power switch can be protected from overcurrent, but the device complexity increases
Solution Approach 1:
The auxiliary winding serves multiple functions simultaneously: it provides current sensing for the PWM controller, enables current limiting protection, and can potentially provide isolation between primary and secondary circuits. This multi-functionality reduces the need for separate protection circuits and components, thereby reducing overall device complexity while maintaining power switch protection
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 reduces manufacturing costs and improves efficiency by eliminating the current-sense resistor, allowing the power converter to operate effectively under light-load conditions without power loss.
Implementation Method 1
A second terminal of the auxiliary winding NA is connected to an anode of the diode 21. The capacitor 22 is connected between a cathode of the diode 21 and the primary ground reference. A supply voltage VCC is obtained across the capacitor 22 to power the switching controller 50.
Data Source
AI summary
A switching controller for power converter comprises a current-sense circuit and a PWM circuit. The current-sense circuit receives high-voltage signal across a first switch to generate a current-sense signal. The PWM circuit generates a switching signal to control the first switch in response to the current-sense signal. The switching controller further comprises a delay circuit. The delay circuit receives the switching signal to generate a delayed switching signal. The current-sense signal and the high-voltage signal ramp up with the same slope during the delayed switching signal is enabled. The current-sense signal will be pulled down to a level of a ground reference during the delayed switching signal is disabled. A delay time provided by the delay circuit avoids the high-voltage signal at the instance which the first switch is being turned off being conducted to a first comparator and a second comparator via a second switch.