Three-Phase DC Motor Drive Circuit With Regenerative Voltage Control
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Solution Overview
Problem
The existing drive circuits for fan motors face a challenge in preventing a drastic rise in power supply voltage when the duty cycle is reduced, particularly due to insufficient capacitor capacity, which can lead to voltage instability.
Innovation Solution
A drive circuit for a three-phase DC motor is designed with a bridge circuit, pre-driver, and a regenerative control circuit that includes a first transistor forming a regenerative path parallel to the low-side transistor, allowing current to escape from the motor coil and stabilizing the power supply voltage by controlling the voltage of the control terminal to a target voltage higher than the power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the duty cycle is drastically reduced to control motor speed, then the motor speed is improved, but the power supply voltage rises drastically causing instability
Solution Approach 1:
A regenerative path is introduced as an intermediary mechanism between the motor coil and power supply line. This path includes a first transistor and regenerative control circuit that act as mediators to redirect and control the current flow, preventing direct current surges to the power supply line when duty cycle is reduced, thus stabilizing the power supply voltage while enabling motor speed control.
Solution Approach 2:
The regenerative control circuit dynamically changes the voltage parameter of the first transistor's control terminal to regulate current flow. By adjusting the voltage of the control terminal of the first transistor, the circuit controls the amount of current flowing through the regenerative path, thereby preventing excessive voltage rise on the power supply line during motor deceleration or low duty cycle operation.
2Adaptability or versatility
If PWM control is used to dynamically control motor revolutions, then the motor speed control is improved, but the power supply voltage stability deteriorates when capacitor capacity is small
Solution Approach 1:
The regenerative path serves as an intermediary that decouples the motor's PWM control operations from direct impact on the power supply voltage. By providing an alternative current path through the first transistor, the system can perform dynamic speed control via PWM without causing excessive voltage fluctuations on the power supply line, even when capacitor capacity is limited.
Solution Approach 2:
The regenerative control circuit implements feedback control by monitoring the regenerative state (when current sinks from the output terminal) and adjusting the voltage of the first transistor's control terminal accordingly. This feedback mechanism ensures that the power supply voltage remains stable by dynamically regulating current flow through the regenerative path based on the actual operating conditions.
Data Source
AI summary
A bridge circuit includes a high-side transistor connected between a power supply terminal and an output terminal, and a low-side transistor connected between the output terminal and a ground terminal. A high-side pre-driver and a low-side pre-driver drive the high-side transistor and the low-side transistor. A first transistor is connected between the output terminal and the ground terminal in a manner to form the regenerative path parallel to the low-side transistor. In a regenerative state in which a current sinks from the output terminal, a regenerative control circuit controls the voltage of a control terminal of the first transistor in a manner that an output voltage of the output terminal approaches a target voltage higher than the power supply voltage of the power supply terminal by a first voltage width.