DC-DC Converter Startup Circuit for Super Capacitor Thermal Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
DC-DC boost converters face challenges in reducing startup time when driving large capacitive loads, particularly with super capacitors, as existing solutions result in prolonged startup durations and excessive power dissipation, risking thermal shutdown.
Innovation Solution
A novel startup circuit that adjusts output current components proportionally to input and output voltages, using a combination of current mirrors and fixed current sources, to maintain power dissipation within safe limits while optimizing startup duration, utilizing programmable parameters via an I2C bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed current source is used to charge the output capacitor during startup, then the startup circuit is simple to implement, but the startup time becomes excessively long when driving large capacitive loads
Solution Approach 1:
The patent applies dynamics by transitioning from a static fixed current source to a dynamic current source that adjusts its output current based on real-time voltage conditions. The current source increases charging current as the output voltage approaches the input voltage, thereby reducing startup time while maintaining safety limits throughout the charging process
Solution Approach 2:
The patent changes the current parameter dynamically during startup by using a current source that varies its output according to the voltage differential between input and output. This parameter change allows the system to optimize charging speed at different stages of the startup process, resolving the contradiction between simple implementation and fast startup
2Loss of time
If the output current is increased to reduce startup time, then the startup duration decreases, but the power dissipation exceeds safe limits causing thermal shutdown
Solution Approach 1:
The patent implements feedback by continuously monitoring the voltage differential between input and output and using this information to adjust the charging current. This feedback mechanism ensures that current is increased only when safe to do so, reducing startup time while preventing power dissipation from exceeding thermal limits
Solution Approach 2:
The system dynamically adjusts current levels based on real-time voltage conditions, allowing higher current when the voltage differential is small (reducing startup time) and lower current when the differential is large (preventing thermal shutdown). This dynamic adaptation resolves the contradiction between fast startup and safe power dissipation
3Productivity
If a large current is used to charge super capacitors quickly, then the charging speed increases, but the transistor experiences excessive power dissipation and potential damage
Solution Approach 1:
The patent changes the current parameter dynamically during the charging process, allowing high current when the transistor is safe to handle it (high productivity) and reducing current when power dissipation becomes dangerous (preventing damage). This parameter adaptation resolves the contradiction between charging speed and transistor safety
Solution Approach 2:
The system uses feedback from voltage sensing to control current levels, ensuring that high charging current is only applied when the voltage differential indicates safe operating conditions. This feedback control enables fast charging of super capacitors while protecting the transistor from excessive power dissipation
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 significantly reduces startup time from 4-5 seconds to approximately 2 seconds while maintaining power dissipation within safe limits, ensuring efficient charging of super capacitors without risking thermal shutdown.
Implementation Method 1
Transistor T2 is connected relative to another P type transistor T3 to form a current mirror circuit. Since the current through the inductor L will be relatively fixed during start up, the voltage drop across the inductor will be minimal so that the source electrode of T2 is essentially at the same potential as the source electrode of T3, namely Vin. The gate electrodes of T2 and T3 are connected together and to the drain of T3 to complete the mirror circuit.
Data Source
AI summary
A startup circuit for use in a DC-DC converter having an input voltage terminal and an output voltage terminal, with the output voltage terminal connected to an output capacitor and with said converter including a pass transistor for transferring charge from the input terminal to the output terminal. The startup circuit includes a control circuit configured to cause the pass transistor to conduct an output current during start up when the output terminal voltage is approaching a final regulated voltage, with the output current being comprised of first and second current components, with the first current component being proportional to the output voltage and the second current component being proportional to the input voltage, with the two components being combined so as to resist changes in the power dissipation in the pass transistor during startup.