Tap Sense Circuit for Zero-Voltage Switching in Power Converters
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Solution Overview
Problem
Conventional switch mode power converters experience significant switching losses due to non-zero voltage across the power switch when turning ON or non-zero current when turning OFF, which increases energy dissipation and costs, particularly because sensing these conditions requires additional pins for the controller, increasing its complexity and cost.
Innovation Solution
A power switch configuration using a four-terminal device with a tap sense circuit that monitors the voltage or current at the tap to determine if the voltage across the power switch is above or below a threshold, allowing the controller to ensure the voltage is zero before turning ON, thus minimizing switching losses without the need for additional pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional sensing methods are used to detect voltage or current for switching control, then switching losses can be minimized, but additional sensing pins are required which increases controller complexity and cost
Solution Approach 1:
The existing pins of the power switch are made to serve dual functions: their primary function and an additional sensing function. The drain pin senses both the voltage for switching control and the output voltage, while the source pin senses both the current for switching control and the output current, eliminating the need for separate sensing pins
Solution Approach 2:
The power switch device itself provides the sensing capability through its existing terminals. The drain and source pins inherently provide the voltage and current information needed for switching control without requiring external sensing circuits or additional pins, making the system self-sufficient
2Speed
If the power switch is turned ON with non-zero voltage across it, then switching speed is maintained, but switching losses increase due to energy dissipation
Solution Approach 1:
The controller uses the sensed voltage at the drain pin to determine when the voltage across the power switch has reached zero before initiating the turn-ON command. This preliminary detection ensures that the switch is turned ON at the optimal moment when voltage is zero, minimizing switching losses while maintaining efficient operation
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 reduces switching losses by ensuring the power switch is only activated when the voltage is near zero, enhancing efficiency and reducing the overall cost of the power converter controller by eliminating the need for extra sensing pins.
Implementation Method 1
the voltage at the tap or current through the first transistor may be monitored to determine the voltage or current at the drain of the power switch
Implementation Method 2
When the power switch is open, voltage across the switch stores energy in the parasitic capacitance. The parasitic capacitance discharges when the power switch closes, dissipating the energy stored in the parasitic capacitance in the resistance of the power switch to produce switching loss
Implementation Method 3
The switched mode power converter controller usually provides output regulation by sensing one or more inputs representative of one or more output quantities and controlling the output in a closed loop. In operation, a switch is utilized to provide the desired output by varying the duty cycle (typically the ratio of the on time of the switch to the total switching period)
Data Source
AI summary
A controller for use in a power converter includes a power switch including a drain, a source, a control input, and a tap. The power switch includes a first transistor coupled to a second transistor, a drain of the first transistor is coupled to the drain of the power switch and the source of the first transistor is coupled to the tap. A tap sense circuit is coupled to the tap. A drive circuit is coupled to receive an indicator signal from the tap sense circuit. The indicator signal is indicative of a voltage at the tap or the current through the first transistor. The drive circuit is coupled to receive a feedback signal representative of an output quantity of the power converter. The drive circuit is coupled to generate a drive signal to control switching of the power switch in response to the indicator signal and the feedback signal.