Power Converter Control Circuit Reducing Current Error
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Solution Overview
Problem
Conventional power converters face challenges in maintaining a fixed output current across a wide range of input voltages due to propagation delay errors, leading to inaccurate cut-off points for power switches and variations in output voltage and current, which degrade line regulation.
Innovation Solution
A control circuit is introduced that includes a peak current emulating unit, error amplifier, and comparator, connected in series with a transformer and power switch, sampling voltages from a sensing resistor to calculate real and initial current sensing voltages, generating an error signal to control the power switch and improve line regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional primary side control is used to reduce circuit cost, then device complexity is reduced, but propagation delay causes current measurement error and degrades output current precision
Solution Approach 1:
The patent applies preliminary action by performing multiple sampling operations at predetermined time points (t1, t2, t3, t4) before the actual peak current occurs. The sampling voltages are captured in advance and then processed through calculation (Vcs5 = Vcs4 + Vcs2 - Vcs1) to obtain the real peak current sensing voltage, thereby compensating for propagation delay effects before they affect the control decision.
Solution Approach 2:
The patent creates a copy of the current sensing process by sampling the sensing resistor voltage at multiple time points and calculating the peak current indirectly through voltage calculations. Instead of directly measuring the peak current at the exact moment it occurs (which is affected by propagation delay), the system creates voltage copies at different time instances and processes them mathematically to reconstruct the accurate peak current value.
2Measurement precision
If propagation delay compensation is implemented through multiple sampling and calculation, then output current precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the current measurement process into multiple discrete sampling events at specific time points (t1, t2, t3, t4) throughout the switching cycle. Each sampling event captures voltage at a particular moment, and these segmented measurements are then combined through calculation to reconstruct the complete peak current information, thereby improving precision without requiring a completely different measurement approach.
Solution Approach 2:
The patent replaces direct mechanical/electrical peak detection (which is subject to propagation delay) with a computational approach. Instead of using a single direct measurement path that suffers from timing delays, the system substitutes multiple delayed measurements with mathematical processing (Vcs5 = Vcs4 + Vcs2 - Vcs1) to achieve accurate peak current detection, thereby eliminating the harmful effect of propagation delay through calculation rather than direct measurement.
3Reliability
If accurate peak current detection is achieved through multiple sampling, then line regulation is improved, but sampling and calculation time increases
Solution Approach 1:
The patent implements periodic action by sampling the sensing resistor voltage at regular, predetermined time intervals (t1, t2, t3, t4) throughout each switching cycle. This periodic sampling ensures that the necessary voltage data points are captured systematically, allowing the calculation of the real peak current (Vcs5) to be performed at consistent intervals, thereby maintaining reliable line regulation with predictable timing.
Solution Approach 2:
The patent performs preliminary sampling actions at specific time points before the peak current occurs, capturing the necessary voltage data (Vcs1, Vcs2, Vcs3, Vcs4) in advance. This preliminary capture of sampling data allows the calculation (Vcs5 = Vcs4 + Vcs2 - Vcs1) to be performed efficiently without waiting for the actual peak current moment, thereby reducing the critical path delay and improving the timing of the control signal generation.
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 control circuit effectively reduces output current errors and enhances line regulation by accurately determining the real peak current and initial current sensing voltages, thereby stabilizing the output current across varying input conditions.
Implementation Method 1
a sensing resistor 330. The control circuit 300 includes a peak current emulating unit 301, an error amplifier 302, a comparator 303 and a control signal generator 304. One end of the peak current emulating unit 301 is coupled to the comparator 303, and the other end of the peak current emulating unit 301 is coupled to the sensing resistor 330 for sampling a plurality of sampling voltages from the sensing resistor 330
Implementation Method 2
A primary side of a transformer of the power converter, a power switch and a sensing resistor are connected in this order and in series to ground
Data Source
AI summary
A control circuit adjusts the output of a power converter by controlling a power switch, in which a primary side of a transformer, the power switch and a sensing resistor are connected in series to ground. The control circuit includes a peak current emulating unit, an error amplifier, a comparator, and a control signal generator. The peak current emulating unit samples sampling voltages from the sensing resistor and obtains a real current sensing voltage and an current sensing voltage using the sampling voltages. The error amplifier receives a fixed reference voltage and a DC voltage generated from the output of the power converter, and generates an error signal. The comparator receives the real current sensing voltage and the error signal and generates a transition signal. The control signal generator receives the transition signal and generates a control signal for controlling the power switch.