Variable DC-DC Converter No-Load Clamp for Output Over-Voltage
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Solution Overview
Problem
Isolated DC-DC converters face issues with over-voltage spikes when unloaded or lightly loaded due to undamped leakage inductance, leading to inefficiencies and limitations in PWM control, as existing solutions either introduce permanent inefficiencies or are costly and complex.
Innovation Solution
A variable DC-DC converter with a voltage clamp mechanism that introduces an internal load only when the converter is unloaded or lightly loaded, using a low-pass filter and a switch to connect or disconnect a shunt load across the output terminals based on voltage thresholds, preventing constant load inefficiencies and allowing efficient operation across varying loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a permanent load resistor is connected across the output to prevent over-voltage spikes, then the over-voltage problem is solved, but the converter efficiency deteriorates due to constant power dissipation
Solution Approach 1:
The patent implements a dynamic load adjustment mechanism where the load resistor is connected only when the output voltage exceeds a predetermined threshold. The control circuit monitors the output voltage and switches the load resistor into or out of the circuit accordingly, making the system adaptive rather than static. This resolves the contradiction by providing over-voltage protection only when needed, eliminating constant power dissipation while maintaining reliability.
2Measurement precision
If the PWM controller reduces the switched-on time to compensate for over-voltage, then the voltage control is improved, but the minimum Ton requirement causes control limitations
Solution Approach 1:
The patent applies preliminary anti-action by proactively damping leakage inductance effects through the load resistor before they can cause severe over-voltage conditions. By connecting the load resistor when voltage reaches the threshold, the system prevents the need for extreme PWM adjustments, ensuring the controller operates within its minimum Ton capabilities while maintaining precise voltage control.
3Measurement precision
If mechanical or software solutions like pulse-skipping are used to address over-voltage, then the voltage control is improved, but the device complexity and reliability are affected
Solution Approach 1:
The patent introduces a load resistor as an intermediary element that passively dampens leakage inductance effects. This simple resistive component acts as a mediator between the transformer and the output, providing voltage stabilization without requiring complex control mechanisms. The load resistor is switched in/out based on voltage thresholds, offering a simpler alternative to pulse-skipping or mechanical solutions while maintaining control precision.
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 effectively dampens over-voltage spikes and maintains stable output voltage without introducing permanent inefficiencies, enabling the converter to operate efficiently across a range of loads while preventing the internal load from being introduced when an external load is connected.
Implementation Method 1
A switch in the DC supply circuit switches on and off a primary winding of the transformer which induces a voltage in the secondary winding which is coupled to the DC output circuit
Implementation Method 2
a voltage clamp connected between the pair of winding terminals. The voltage clamp includes a switch, connected between the pair of winding terminals, to connect or disconnect a shunt load between the pair of output terminals
Implementation Method 3
a low-pass filter connected between the pair of winding terminals and including a filter output, wherein the filter output outputs a control signal to the switch
Data Source
AI summary
A variable DC-DC converter includes a no-load voltage clamp in which a rectified, filtered, and loaded control signal drives a switch. The switch switches in a load resistance across the output terminals of the converter when the output terminals are unloaded or lightly loaded. Due to a combined rectification, smoothing, and filtering operation of the control signal circuit, the control signal provides a steady voltage of the output voltage selected by a user of the converter based on predetermined output requirements. The control signal is therefore not subject to the voltage spikes that the main output is subject to. The circuit compares the control signal to the output voltage, and switches in the load resistance when the voltage at the output rises above the control signal.