Boost Converter Dummy Load Control for Skip Mode Prevention
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Solution Overview
Problem
Conventional synchronous boost converters struggle to maintain high efficiency and avoid skip mode operation when operating in diode mode, particularly in applications where the input voltage is near or slightly higher than the target output voltage, and under very light load conditions.
Innovation Solution
A DC-DC boost converter circuit with a variable load circuit that sinks a load current proportional to the input voltage, controlled by a control circuit to operate in asynchronous mode, using a differential input pair and trimmable resistors and current mirrors to adjust the load current based on input voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a synchronous boost converter operates in diode mode with the high-side transistor kept off, then the converter can handle input voltages near or slightly higher than the output voltage, but the converter may enter skip mode under light load conditions causing larger output voltage ripple and variable frequency
Solution Approach 1:
A dummy load circuit is introduced as an intermediary component to sink excess current from the converter output. This dummy load prevents the converter from entering skip mode by providing a minimum load current, thereby maintaining continuous operation and stable output voltage regulation even under light external load conditions.
Solution Approach 2:
The dummy load circuit dynamically adjusts its current sinking characteristic based on the input voltage level. When the input voltage is close to or slightly higher than the output voltage, the dummy load activates to sink appropriate current and prevent skip mode. The circuit parameters are designed to automatically adapt to different operating conditions.
2Loss of energy
If a synchronous boost converter operates in diode mode, then high efficiency can be maintained, but unnecessary current waste occurs without proper load management
Solution Approach 1:
The dummy load circuit incorporates feedback mechanisms that monitor the converter's operating conditions, including input voltage and output current. Based on this feedback, the circuit intelligently activates or deactivates the dummy load function, ensuring current is sunk only when necessary to prevent skip mode, thereby minimizing energy waste while maintaining efficiency.
3Reliability
If a fixed dummy load is used to prevent skip mode, then continuous operation is maintained, but the load circuit complexity increases and efficiency decreases due to constant current sinking
Solution Approach 1:
The dummy load circuit is designed with dynamic characteristics, allowing it to transition between active and inactive states based on operating conditions. The circuit includes voltage-dependent current sources and control logic that automatically adjust the dummy load current, transforming a potentially static complex circuit into a dynamic, condition-responsive system that simplifies overall design.
Data Source
AI summary
A DC-DC boost converter includes an input receiving an input voltage and an output producing an output voltage. A switching stage is formed by a low-side transistor arranged between a switching node and a ground node, and a high-side transistor arranged between the switching node and the output. The high-side transistor includes a body diode having an anode coupled to the switching node and a cathode coupled to the output. The converter is controlled in an asynchronous operation mode where the low-side transistor is driven alternately to a conductive state and a non-conductive state, and the high-side transistor is driven steadily to a non-conductive state. A variable load circuit is selectively coupled between the two output terminals when the converter is in the asynchronous operation mode in order to sink a load current having a value that is a function of a value of the input voltage.