Peak Current Control Circuit With Dynamic Reference Compensation
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Solution Overview
Problem
The existing peak current control methods in switching mode power supplies suffer from inaccuracies in output current due to propagation delays in turning off the transistor, leading to errors in peak current and voltage, which vary with changes in input signal or inductance.
Innovation Solution
A peak current control circuit that includes a current sense circuit, a reference signal generator, and a comparator to generate a varying reference signal based on the switching control signal, ensuring the power switch is turned off when the current in the energy storage component reaches this signal, thereby maintaining a constant peak current and improving output current accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed reference signal is used in peak current control, then the control circuit is simple, but the output current accuracy deteriorates due to propagation delays varying with input voltage and inductance
Solution Approach 1:
The reference signal is changed from a fixed value to a dynamic value that varies with the switching cycle. Specifically, the reference signal is generated by dividing a fixed reference voltage by the switching cycle period (Tsw), making it proportional to 1/Tsw. This dynamic adjustment compensates for propagation delays that vary with operating conditions, thereby improving output current accuracy without significantly increasing circuit complexity.
Solution Approach 2:
The reference signal parameter is changed from a constant value to a variable value that depends on the switching cycle period. By making the reference signal proportional to 1/Tsv, the system adapts to varying propagation delays caused by different input voltages and inductance values, thus improving measurement precision while maintaining reasonable circuit complexity.
2Measurement precision
If propagation delay is compensated by adjusting reference signal, then output current accuracy is improved, but device complexity increases
Solution Approach 1:
The control circuit is designed to perform multiple functions using the same components. The reference signal generator circuit not only provides the reference signal for current comparison but also inherently compensates for propagation delays by making the reference signal proportional to 1/Tsv. This multi-functionality approach improves accuracy without adding separate compensation circuits, thus limiting the increase in device complexity.
Solution Approach 2:
The system uses feedback from the switching cycle period to adjust the reference signal dynamically. By measuring the switching cycle period and using it to generate an appropriately scaled reference signal, the system automatically compensates for propagation delays without requiring external intervention or complex calibration circuits.
3Reliability
If the transistor is turned OFF after propagation delay, then the control signal has sufficient time to propagate, but the peak current control accuracy deteriorates
Solution Approach 1:
The reference signal is prepared in advance with the appropriate magnitude based on the expected switching cycle period. By pre-calculating the reference signal as proportional to 1/Tsv, the system accounts for the propagation delay before it occurs, allowing the transistor to be turned off at the correct moment despite the delay, thus maintaining both reliability and accuracy.
Solution Approach 2:
The system preemptively compensates for the harmful effect of propagation delay by adjusting the reference signal magnitude before the comparison occurs. By making the reference signal proportional to 1/Tsv, the system counteracts the accuracy-deteriorating effect of propagation delay in advance, allowing reliable control signal propagation without sacrificing peak current control accuracy.
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 solution ensures a constant peak current by adjusting the reference signal to account for propagation delays, reducing errors and enhancing the accuracy of the output current in switching mode power supplies.
Implementation Method 1
When the transistor Q1 is turned ON, a primary current IP flows through the primary winding NP, which starts building up a magnetic energy
Implementation Method 2
A secondary winding Ns is magnetically coupled to the primary winding NP and includes a secondary diode D1 and a capacitor Co
Data Source
AI summary
A switching mode power supply with improved peak current control is disclosed. A varying reference signal is adopted to limit the peak current in the energy storage component. The varying reference signal is an exponential function of a time period when a power switch is ON, wherein the power switch is coupled to the energy storage component. The varying reference signal may be generated by a circuit comprising a RC circuit and one or several voltage sources.