PWM Converter Control With Adjustable Cycle Period Range
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Solution Overview
Problem
Existing switching power converters have a limited conversion ratio due to preset minimum on-time and off-time, restricting the range of output and input voltage adjustment.
Innovation Solution
A conversion control circuit that adjusts the cycle period of the PWM signal by extending on-time or off-time based on output power characteristics, allowing the conversion ratio to approach 0 or 1, using an error amplification circuit, ramp signal generation, and adjustable oscillation to adaptively control the switching cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the switching frequency is determined by a fixed oscillation circuit, then the control is simple, but the conversion ratio has upper and lower limits that restrict the applicable output voltage and input voltage range
Solution Approach 1:
The oscillation circuit is made dynamically adjustable by introducing a DAC that can change the oscillation frequency based on feedback signals. The switching cycle period is no longer fixed but adapts according to the actual conversion ratio requirements, allowing the circuit to extend its applicable voltage range while maintaining controlled complexity through automated adjustment.
Solution Approach 2:
The oscillation frequency parameter is made variable through DAC control. By changing the frequency parameter dynamically based on feedback, the circuit can adjust the switching cycle period to accommodate different conversion ratios, thereby expanding the applicable output and input voltage ranges without proportionally increasing circuit complexity.
2Adaptability or versatility
If the on-time and off-time are extended to increase the cycle period, then the conversion ratio can approach 0 or 1, but the switching frequency becomes variable
Solution Approach 1:
A feedback mechanism is implemented where the actual conversion ratio is detected and used to control the DAC, which in turn adjusts the oscillation frequency. This closed-loop feedback ensures that the switching cycle period adapts appropriately to achieve conversion ratios close to 0 or 1 while maintaining system stability through automated regulation rather than manual or erratic adjustment.
3Adaptability or versatility
If a fixed switching cycle period is used, then the timing control is simple, but the on-time and off-time cannot be sufficiently extended to achieve extreme conversion ratios
Solution Approach 1:
A DAC is introduced as an intermediary component between the feedback signal and the oscillation circuit. The DAC converts the feedback information into appropriate frequency control signals, enabling the cycle period to be adjusted without directly modifying the oscillation circuit structure. This intermediary approach achieves extreme conversion ratios while keeping the adjustment mechanism relatively simple and modular.
Data Source
AI summary
A conversion control circuit is configured to generate a PWM (pulse width modulation) signal to control a power switch for switching an inductor to convert an input voltage to an output voltage. The steps of generating the PWM signal includes: enabling the PWM signal at a rising edge of a clock signal to turn on the power switch; disabling the PWM signal to turn off the power switch when an on-time exceeds a predetermined minimum on-time and the output voltage has reached an output level; triggering a next rising edge of the clock signal when the off-time exceeds a predetermined minimum off-time, the output voltage has not reached the output level, and a present cycle period of the clock signal has reached a predetermined cycle period.