Slew-Rate Control Circuit for Stable Power Transistor Switching
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Solution Overview
Problem
Conventional pre-drive circuits struggle to maintain a consistent transition time period for output power transistors during turn-on and turn-off due to variations in gate capacitance and temperature changes, leading to inefficiencies in switching loss and noise generation.
Innovation Solution
A microcontroller with a slew-rate control circuit that measures and adjusts the constant current set value for the pre-drive circuit to maintain a predetermined transition time period, using a measuring circuit to monitor the drain-to-source voltage transitions and a microprocessor to control the constant current sources, ensuring consistent transition times despite variations in gate capacitance and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a constant current source is used to charge and discharge the gate of the output power transistor, then the transition time period can be kept constant, but the transition time period varies due to gate capacitance variations and temperature changes
Solution Approach 1:
The patent implements a feedback mechanism where the microprocessor measures the actual transition time period of the output power transistor and adjusts the constant current set value accordingly. The measuring circuit monitors the drain-to-source voltage transitions, and the microprocessor uses this information to dynamically control the constant current sources, ensuring the transition time period remains at the predetermined value despite gate capacitance variations and temperature changes.
Solution Approach 2:
The patent changes the current parameter dynamically by adjusting the constant current set value based on measured transition time periods. The microprocessor modifies the current magnitude to compensate for variations in gate capacitance and temperature effects, thereby maintaining consistent transition time periods for the output power transistor.
2Loss of energy
If the transition time period is not kept constant, then switching loss and power current noise increase, but maintaining constant transition time requires complex control circuits
Solution Approach 1:
The patent integrates multiple functions into the microprocessor, which not only controls the constant current sources but also measures the transition time period and adjusts the current set value dynamically. This multi-functional approach avoids the need for separate complex control circuits while achieving constant transition time period control, thereby reducing switching loss without significantly increasing device complexity.
Solution Approach 2:
The system performs self-adjustment by using the microprocessor to automatically measure the transition time period and modify the constant current set value based on actual performance. This self-service mechanism eliminates the need for external complex control circuits, as the system autonomously optimizes its own operation to maintain constant transition times and minimize switching losses.
3Object-generated harmful factors
If larger noise filter circuits are used to reduce power current noise, then noise is reduced, but the inverter circuit size and cost increase
Solution Approach 1:
The patent applies preliminary action by controlling the transition time period of the output power transistor to be constant through dynamic current adjustment. By preemptively managing the switching characteristics, the system prevents the generation of excessive power current noise in the first place, thereby reducing or eliminating the need for large noise filter circuits and decreasing overall circuit size and cost.
Data Source
AI summary
A microcontroller with a slew-rate control circuit according to an embodiment includes a pre-drive circuit configured to charge and discharge a gate of an output power transistor with a constant current, a measuring circuit configured to measure a transition time period during which a drain-to-source voltage of the output power transistor makes a transition between a first voltage and a second voltage, and a microprocessor. The microprocessor controls a constant current set value of the pre-drive circuit such that the transition time period is a predetermined time period.