PWM Controller Power Limiter for Output Power Compensation
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Solution Overview
Problem
Power converters face challenges in maintaining consistent maximum output power across varying input voltages and frequencies, leading to inefficiencies and potential overload or short-circuit issues, particularly during low-line voltage and heavy-load conditions.
Innovation Solution
A control circuit with a power limiter and delay counter is introduced, which generates a saw-limited signal to flatten the limit signal before output voltage generation, ensuring identical output power limits for both low and high line voltages, and includes a feedback detector to manage the power switch effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a traditional PWM controller is used to regulate output voltage, then the power converter can operate with simple control circuitry, but the maximum output power varies with input voltage and delay time, causing inconsistency in power limiting
Solution Approach 1:
The patent applies preliminary action by generating a delay compensation signal in advance that anticipates and compensates for the delay time TD in the control circuit. The saw-tooth wave generator produces a compensation signal before the PWM signal is generated, which is then used to adjust the maximum output power limit accordingly. This ensures that the power limit is set correctly in advance, accounting for the known delay time, thereby maintaining consistent maximum output power across different input voltages and delay conditions.
2Reliability
If the control circuit disables PWM signal when current exceeds maximum threshold, then overload protection is achieved, but there is a delay time causing the power switch to remain on longer than intended, increasing actual maximum output power
Solution Approach 1:
The patent applies preliminary action by pre-calculating and compensating for the delay time TD in the control circuit. A delay compensation signal is generated in advance based on the known delay characteristics, and this compensation signal is used to adjust the maximum output power limit before the PWM signal is generated. This allows the system to account for the delay time proactively, ensuring that the power switch is turned off at the correct moment despite the inherent delay in the control circuit.
3Ease of manufacture
If the power limit is set based on a fixed current threshold, then the control circuit is simple to implement, but the actual maximum output power becomes dependent on input voltage and delay time, violating safety regulations
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the maximum output power limit based on the input voltage VIN and delay time TD. Instead of using a fixed current threshold, the system modifies the power limit parameter in real-time according to the actual operating conditions. The saw-tooth wave generator produces a compensation signal that reflects the relationship between input voltage and delay time, and this signal is used to adjust the maximum output power limit accordingly, ensuring compliance with safety regulations across different input voltage conditions.
4Productivity
If the switching frequency is increased to improve power converter efficiency, then the power converter operates more efficiently, but the delay time becomes more significant relative to the switching period, causing greater deviation in maximum output power
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the maximum output power limit based on the switching period TS and delay time TD relationship. The saw-tooth wave generator produces a compensation signal that accounts for the ratio of delay time to switching period, allowing the system to maintain precise control of maximum output power even at high switching frequencies. This compensation mechanism ensures that the power limit remains accurate regardless of the switching frequency, thereby maintaining both efficiency and control precision.
Data Source
AI summary
A PWM controller compensates a maximum output power of a power converter having a power switch. The PWM controller includes an oscillator for generating a saw signal and a pulse signal, a power limiter coupled to the oscillator for generating a saw-limited signal in response to the saw signal, and a PWM unit coupled to the power limiter and the oscillator to generate a PWM signal for controlling the power switch in response to the saw-limited signal and the pulse signal. The saw-limited signal has a level being flattened during a period of time before an output voltage is generated, and is then transformed to a saw-limited waveform after the period of time.