Active Clamp Flyback Circuit for Low-Ringing ZVS Power Conversion
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Solution Overview
Problem
Existing active clamp flyback converters experience ringing at the secondary side switch node, leading to noise and the need for larger noise suppression components, which hinders downsizing and efficiency.
Innovation Solution
A switching power supply circuit with a transformer, driver switch, active clamp switch, bulk capacitor, rectifiers, tank and output capacitors, and a control circuit that clamps the primary and secondary side switch nodes to the bulk and output capacitors, respectively, ensuring zero voltage switching and reducing ringing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a typical flyback converter uses an RCD snubber to dissipate leakage inductor energy, then the circuit is simple to implement, but the loss increases in proportion to switching frequency and device downsizing is hindered
Solution Approach 1:
The patent converts the harmful leakage inductor energy that was previously dissipated as loss into a useful resource by charging the clamp capacitance. The active clamp switch captures the leakage energy during the switch-off period and releases it during power transfer to the secondary side, transforming energy waste into beneficial energy recovery that reduces overall losses and enables higher switching frequencies
Solution Approach 2:
The patent changes the operational parameters by introducing an active clamp switch that operates in complementarity with the main switch. This allows the circuit to operate at higher switching frequencies without proportional increase in loss, fundamentally changing the relationship between switching frequency and energy loss that characterized traditional RCD snubber circuits
2Productivity
If switching frequency is increased to improve power density, then efficiency improves, but leakage inductor energy loss increases proportionally and device downsizing is hindered
Solution Approach 1:
The active clamp circuit converts the previously harmful leakage energy into a beneficial resource that supports higher frequency operation. By capturing and recycling leakage energy through the clamp capacitance, the system achieves higher power density through increased switching frequency without the proportional increase in losses that would otherwise occur
3Power
If the secondary side switch node voltage increases to handle higher power, then power capacity improves, but ringing amplitude increases causing noise and requiring larger noise suppression components
Solution Approach 1:
The patent converts the ringing phenomenon, previously a harmful noise source, into a beneficial resonant oscillation that aids in zero-voltage switching. The resonant current generated by the leakage inductor and clamp capacitance combination is harnessed to achieve ZVS at the primary switch, transforming what was considered a problem into a useful mechanism for reducing switching losses and noise
Solution Approach 2:
The clamp capacitance acts as an intermediary element that mediates between the leakage inductor and the rest of the circuit. It absorbs the high-frequency ringing energy and converts it into a controlled resonant oscillation that supports ZVS operation, preventing the ringing from manifesting as harmful noise while still allowing high power capacity
4Loss of energy
If active clamp switches are controlled to achieve ZVS, then switching loss and noise are significantly reduced, but circuit complexity increases
Solution Approach 1:
The circuit is designed to achieve ZVS through self-service mechanisms where the resonant oscillation naturally creates the conditions for zero-voltage switching. The leakage inductor and clamp capacitance form a resonant circuit that automatically generates the necessary current waveform, reducing the need for complex external control circuitry while maintaining low switching losses
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 circuit achieves a compact, highly efficient, and low-noise power supply with reduced component size and cost, utilizing zero voltage switching and optimized control to minimize losses and noise.
Implementation Method 1
a transformer with a primary winding and a secondary winding
Implementation Method 2
a driver switch to drive the transformer, an active clamp switch that clamps a primary side switch node when the driver switch is turned off
Implementation Method 3
a bulk capacitor to discharge clamp energy, a tank capacitor, an output capacitor
Data Source
AI summary
An isolated switching power supply circuit is compact, high-efficiency, and low noise. It includes a transformer T1 which has a primary winding wound with NP turns and a secondary winding wound with NS turns, a drive switch Q1 and an active clamp switch Q2 configuring a primary side half-bridge, a boost capacitor CBULK1 that charges a discharge energy of the transformer, rectifier diodes D1 and D2 connected in series, a tank capacitor CT1, and an output capacitor COUT1. A secondary side winding voltage, when the drive switch Q1 or the active clamp switch Q2 is on, is held in the tank capacitor CT1, and by superimposing the secondary winding voltage, when the drive switch Q1 or the active clamp switch Q2 is off, on the voltage held in the tank capacitor CT1, the configuration is such that output voltage VOUT equals boosted voltage VBULK times (NS divided by NP).