DC-DC Converter Light Load Efficiency via Rectifier Timing
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Solution Overview
Problem
Synchronously rectifying switching regulators experience a decrease in power efficiency at light loads, leading to complications in EMI filter design, increased noise, and abnormal noise generation due to changes in switching frequency.
Innovation Solution
The on-time of the rectifying switching element is extended by delaying its turn-off timing at light loads, allowing energy accumulation without altering the switching frequency, even when the driving switching element's on-time is shorter than the minimum required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PFM control or PDM control is performed at light load to reduce power consumption, then power efficiency is improved, but switching frequency changes causing EMI filter design complications and noise increase
Solution Approach 1:
The patent applies dynamics by making the rectifying switching element's on-time variable rather than fixed. At light loads, the on-time is dynamically extended beyond the minimum required time, allowing the circuit to maintain continuous inductor current and constant switching frequency while still achieving efficient power conversion. This dynamic adjustment resolves the contradiction by enabling both power efficiency improvement and EMI filter design simplification.
Solution Approach 2:
The patent changes the time parameter of the rectifying switching element's on-duration from a fixed minimum value to a variable value that extends beyond the minimum at light loads. This parameter change allows the switching frequency to remain constant while improving power efficiency, thereby avoiding EMI filter design complications that would arise from frequency variations.
2Loss of energy
If driving switching element on-time is reduced at light load to improve power efficiency, then power loss decreases, but switching frequency drops into audible range causing abnormal noise
Solution Approach 1:
The patent uses dynamics to adjust the rectifying switching element's on-time based on load conditions. At light loads, the on-time is extended beyond the minimum required duration, which maintains the switching frequency at its designated value and prevents it from dropping into the audible range. This dynamic adjustment simultaneously achieves power loss reduction and abnormal noise prevention.
Solution Approach 2:
The rectifying switching element acts as an intermediary that extends the effective on-time beyond the minimum required by the driving switching element. This intermediary action maintains continuous inductor current and stabilizes the switching frequency, preventing audible noise while still achieving the power loss benefits of light-load optimization.
3Ease of operation
If rectifying switching element turns off at minimum on-time at light load, then circuit operation is simplified, but reverse direction current flows causing power efficiency degradation
Solution Approach 1:
The patent applies preliminary action by extending the rectifying switching element's on-time beyond the minimum required duration before the inductor current would naturally fall to zero. This preliminary extension ensures continuous current flow and prevents reverse direction current, thereby maintaining power efficiency while keeping the circuit operation relatively simple through a single switching element control strategy.
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
This approach enhances power efficiency, simplifies EMI filter design, reduces noise, and prevents abnormal noise from entering the audible range by maintaining consistent switching frequency.
Implementation Method 1
an on-time of the rectifying switching element is controlled to become longer as a load becomes lighter by delaying a timing of turning off a rectifying switching element in order to accumulate the energy from an output of the DC-DC converter at a time of a light load
Data Source
AI summary
A control technology which eliminates the need for changing the switching frequency even under light load where the on-time of a drive switching element becomes shorter than a minimum on-time dependent on the characteristics of the circuit in a synchronous rectification switching regulator. The synchronous rectification switching regulator includes a drive switching element for storing energy in a coil by applying a DC input voltage from a DC power supply to an inductor and permitting a current to flow, and a rectification switching element for rectifying the current of the inductor during an energy discharge period where the drive switching element is turned off. The timing for turning off the rectification switching element under light load is delayed so as to store energy in the inductor from the output, and the on-time is controlled to become longer as the load becomes lighter by the output from an error amplifier.