Motor Driving Circuit Reducing Switching Loss via Push-Pull Amplifiers
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Solution Overview
Problem
Traditional motor driving circuits for heat-dissipation fans in lightweight electronic products, such as notebook computers, suffer from high switching loss due to long charge/discharge periods of PMOS transistors, leading to increased switching loss and insufficient derating of junction temperature, which affects system stability and performance.
Innovation Solution
A motor driving circuit design that includes a motor driving unit with push-pull output and control units, utilizing push-pull amplifiers to generate amplified currents for the first and third switches, reducing their charge/discharge periods and switching loss, thereby improving fan efficiency and resolving junction temperature issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional PWM control is used to drive the motor, then the circuit structure is simple, but the PMOS transistor has long charge/discharge periods resulting in high switching loss
Solution Approach 1:
The patent introduces push-pull amplifiers as intermediary components between the control unit and the motor driving unit. These amplifiers act as mediators that provide strong driving current to rapidly charge/discharge the gate capacitance of PMOS transistors, thereby reducing switching loss without fundamentally changing the overall circuit topology
Solution Approach 2:
The patent changes the current parameter by using push-pull amplifiers to provide high current driving capability. This parameter change enables rapid charging and discharging of the gate capacitance, reducing the switching time and consequently the switching loss of the PMOS transistors
2Speed
If high frequency switching is performed, then the motor control precision is improved, but the switching loss increases and junction temperature rises
Solution Approach 1:
The patent applies preliminary action by pre-charging the gate capacitance to the required voltage level before the actual switching operation. The push-pull amplifiers are ready to immediately provide the necessary charging current when switching is required, enabling fast switching without excessive loss accumulation
Solution Approach 2:
The patent uses the push-pull amplifier configuration to rush through the charging and discharging of the gate capacitance in minimal time. By providing strong bidirectional current driving capability, the amplifier quickly moves the PMOS transistor through the critical switching transition region, minimizing the time spent in the high-loss state
3Loss of time
If the driving current is increased to reduce charge/discharge periods, then the switching speed improves, but the circuit complexity increases
Solution Approach 1:
The patent employs dynamic circuit elements in the form of push-pull amplifiers that can rapidly switch between sourcing and sinking current. This dynamic behavior allows the circuit to provide high driving current only when needed during switching transitions, rather than maintaining high current continuously, thus reducing the charge/discharge period without proportionally increasing overall circuit complexity
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
The design effectively reduces switching loss and enhances fan efficiency by shortening the charge/discharge periods of the first and third switches, leading to improved junction temperature management and increased switching speed, thus addressing the inefficiencies of traditional circuits.
Implementation Method 1
there is capacitance (or parasitic capacitance) existing between the gate and the source of the PMOS transistor. The charge/discharge periodc associated with the capacitance depends on the driving current.
Data Source
AI summary
The present invention provides a motor driving circuit to reduce switching loss, which is applied to a motor. The motor driving circuit comprises a motor driving unit, a push-pull output unit, and a control unit. The control unit is coupled to the motor driving unit and the push-pull output unit. The control unit transmits a driving voltage to drive the push-pull output unit such that the push-pull output unit generates amplified currents which are transmitted to the motor driving unit. The motor driving unit reduces charge/discharge periods thereof based on the received amplified currents.