Power Tool Drive Circuit Parasitic Diode Heat Reduction
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Solution Overview
Problem
Power tools experience significant temperature rise and power loss due to parasitic diodes in switches, especially under heavy load and high current conditions, leading to inefficiency and potential damage.
Innovation Solution
A power tool control method that synchronously outputs PWM signals to high-side and low-side switches, adjusting their states to direct current flow through the switches instead of parasitic diodes, thereby reducing heat generation and power loss. The controller also includes a temperature sensor to monitor and manage drive circuit temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If switches are toggled from on state to off state in conventional drive circuits, then the motor can be controlled, but current passes through parasitic diodes causing temperature rise and power loss
Solution Approach 1:
The controller outputs control signals to switches in advance to ensure proper timing. Specifically, the high-side switch is turned off before the low-side switch is turned on, preventing current from passing through parasitic diodes. This preliminary action of controlling switch timing resolves the contradiction by maintaining motor control capability while eliminating energy loss through parasitic diode conduction.
Solution Approach 2:
The invention changes the timing parameters of control signals to switches. By adjusting the duty cycle and timing of PWM signals, the controller ensures that switches transition states without current flowing through parasitic diodes. This parameter change resolves the contradiction by optimizing switch timing to prevent energy loss while maintaining motor control.
2Speed
If switches are toggled frequently to control motor under heavy load, then motor response is improved, but heat generation in switches increases significantly
Solution Approach 1:
The controller prepares control signals in advance with proper timing to turn off high-side switches before turning on low-side switches. This preliminary action prevents current from flowing through parasitic diodes during frequent switching operations, thereby reducing heat generation while maintaining fast motor response under heavy load conditions.
Solution Approach 2:
The invention converts the potential harmful effect of frequent switching (heat generation through parasitic diodes) into a beneficial outcome by controlling switch timing. By ensuring switches are properly timed, the frequent switching operations that would normally generate heat instead efficiently control the motor without excessive temperature rise, turning a potential harm into a benefit.
3Device complexity
If conventional drive circuits are used with parasitic diodes, then circuit simplicity is maintained, but temperature rise causes reliability issues
Solution Approach 1:
The controller uses feedback from temperature sensors and current detection to adjust control signals to switches. When temperature or current reaches certain thresholds, the controller modifies switching timing to prevent excessive heat generation through parasitic diodes. This feedback mechanism maintains simple circuit structure while improving switch reliability by dynamically adjusting operation to avoid overheating.
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 effectively suppresses temperature rise and power loss in the drive circuit, enhancing the efficiency and longevity of power tool components while preventing overheating.
Implementation Method 1
The first control signal output by the controller is a first PWM signal and the second control signal output by the controller is a second PWM signal
Implementation Method 2
The controller also includes a temperature sensor to monitor and manage drive circuit temperature
Implementation Method 3
The parasitic diode heats up due to the internal resistance, rising the temperature of the switch of the parasitic diode and the drive circuit
Data Source
AI summary
A power tool has a functional component, a motor, a power supply module, a controller and a drive circuit including a first drive terminal and a second drive terminal respectively electrically connected to a first power terminal and a second power terminal of the power supply module, multiple high-side switches wherein high-side terminals of the high-side switches are respectively electrically connected to the first drive terminal, and multiple low-side switches wherein low-side terminals of the low-side switches are respectively electrically connected to the second drive terminal. The controller is configured to output a first control signal to one high-side switch to place it in an on or off state and output a second control signal to one low-side switch to place it in the other state. The low-side terminal of one high-side switch is connected to the high-side terminal of one low-side switch.