Volt-Second Clamp Accuracy in Isolated DC/DC Converters
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Solution Overview
Problem
Existing volt-second clamp systems in isolated DC/DC converters face inaccuracies when input voltage varies, particularly when the input voltage is low, leading to potential transformer core saturation due to the exponential nature of the clamp and limitations in reference voltage adjustment.
Innovation Solution
A novel volt-second clamp system that adjusts the reference voltage inversely proportional to the input voltage by using a multiplier/divider circuit to correct the reference value, eliminating the need for complex feedback loops and minimizing inaccuracies associated with integrated circuit capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed reference voltage is used in the volt-second clamp circuit, then the circuit is simple to implement, but the accuracy deteriorates when input voltage varies
Solution Approach 1:
The reference voltage is changed from a fixed value to a dynamically adjustable value that varies inversely with the input voltage. The PWM controller automatically adjusts the reference voltage based on the detected input voltage level, ensuring accurate volt-second limiting across the entire input voltage range without requiring complex external circuitry.
Solution Approach 2:
The reference voltage parameter is made variable rather than fixed. The PWM controller modifies the reference voltage parameter in real-time according to the input voltage conditions, allowing the volt-second clamp to maintain high accuracy under varying operating conditions while keeping the overall circuit design relatively simple.
2Measurement precision
If the reference voltage is adjusted to improve low voltage accuracy, then the accuracy improves, but the circuit complexity increases
Solution Approach 1:
The PWM controller is designed to perform multiple functions including both PWM generation and volt-second limiting with automatic reference voltage adjustment. By integrating the reference voltage adjustment capability within the existing PWM controller architecture, the patent avoids adding separate complex adjustment circuits while achieving improved accuracy across all input voltage ranges.
3Measurement precision
If external RC circuits are used for volt-second limiting, then the accuracy can be good, but the circuit requires additional external components
Solution Approach 1:
The volt-second limiting function is merged with the PWM control function in a single integrated PWM controller. The reference voltage adjustment mechanism is combined with the existing PWM generation circuitry, eliminating the need for separate external RC timing circuits and reducing the overall component count while maintaining or improving accuracy.
Data Source
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AI summary
A novel system and methodology for providing a volt-second clamp. A DC/DC conversion system configured for producing an output voltage in response to an input voltage has a transformer with a primary winding responsive to the input voltage and a secondary winding for producing the output voltage. The conversion system has a power switch coupled to the primary winding of the transformer and controlled with a converter control signal, such as a PWM control signal. The power switch is further controlled by a comparator that compares an input value supplied to its input with a variable reference value so as to prevent magnetic flux density of the transformer from increasing to an undesired level. The input value of the comparator is produced by a comparator input circuit as a function of the input voltage and an on-time of the power switch. A reference circuit produces the reference value that varies as a function of the input voltage.