PWM Controller With Adjustable Minimum Duty Cycle
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Solution Overview
Problem
Conventional PWM control circuits for single-phase brushless electric motors face limitations such as fixed minimum duty cycle settings, high power consumption at high voltages, inadequate starting power at low voltages, and inability to maintain non-zero motor speed when the input pulsed signal duty cycle is zero.
Innovation Solution
A PWM controller that accepts a pulsed input signal and generates an output PWM signal with an adjustable minimum duty cycle, correlated to the input signal's duty cycle, and adjustable in response to power supply voltage changes, using a signal conversion circuit, triangle wave generation circuit, and pulse generation circuit to ensure minimum duty cycle is maintained across varying voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed minimum duty cycle setting is used in conventional PWM controllers, then the circuit structure is simple, but the power consumption is high at high power supply voltages and inadequate starting power at low power supply voltages
Solution Approach 1:
The patent implements a dynamic minimum duty cycle adjustment mechanism where the minimum duty cycle is no longer fixed but varies according to the power supply voltage. The control circuit automatically adjusts the minimum duty cycle parameter based on detected voltage levels, making the system adaptive to different operating conditions and reducing power consumption at high voltages while ensuring adequate starting power at low voltages.
Solution Approach 2:
The patent changes the parameter of minimum duty cycle from a fixed value to a variable value that depends on power supply voltage. By making the minimum duty cycle parameter changeable based on voltage conditions, the system optimizes power consumption characteristics across different operating ranges without requiring complex external control mechanisms.
2Adaptability or versatility
If conventional PWM controllers accept pulsed control input signals, then the control flexibility is improved, but the motor speed cannot be maintained at non-zero when the duty cycle of the input pulsed signal is zero
Solution Approach 1:
The patent implements a preliminary anti-action mechanism by detecting when the input pulsed signal duty cycle approaches zero and proactively applying a compensatory minimum duty cycle. This prevents the motor speed from dropping to zero by counteracting the effect of zero-duty-cycle input signals, ensuring continuous motor operation and maintaining system reliability while preserving control flexibility.
3Device complexity
If the triangle wave signal is not adjustable in response to power supply voltage changes, then the circuit is simpler, but the duty cycle cannot be optimized for low voltage conditions
Solution Approach 1:
The patent implements a feedback mechanism where the power supply voltage is continuously monitored and used to adjust the triangle wave signal characteristics. The control circuit detects voltage changes and automatically modifies the triangle wave parameters accordingly, creating a closed-loop system that optimizes duty cycle performance based on actual operating conditions without requiring complex manual intervention.
Data Source
AI summary
A pulse width modulated (PWM) controller has an input terminal for receiving a pulsed input signal having a first duty cycle, a power supply terminal for receiving a power supply voltage. a minimum duty cycle reference voltage signal, and a control circuit for providing a pulse-width-modulated (PWM) output signal having a second duty cycle related to the first duty cycle of the pulsed input signal. The PWM output control signal having a minimum duty cycle that is adjustable in response to a change in the power supply voltage. In an embodiment, the second duty cycle and the first duty cycle are correlated in a substantially linear relationship. In an embodiment, the PWM control circuit also has a triangle wave generation circuit for generating a triangle wave signal configured to oscillate between an upper limit voltage and a lower limit voltage, which are adjustable in response to a change in the power supply voltage.