| Overview of secondary side synchronous rectification malfunction |
| ・ |
Although it uses secondary side synchronous rectification, the power supply efficiency is low. |
| ・ |
The designed rated output cannot be achieved. |
| ・ |
Increasing the load current of the secondary side synchronous rectifier
circuit will damage the circuit. |
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| ↓Waveform when the output current is small. This is fine. |
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| ↓The problematic waveform occurs when the load current is increased. |
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| Basic operation of secondary side synchronous rectification |
| ① |
When the primary side is turned off, the MOSFET gate is turned on at the maximum negative Vds voltage. |
| ② |
When the negative Vds voltage is at the minimum, the MOSFET gate is turned off (about 0V). There is a short period of time when current flows through the body diode.(The gate is not turned on until Vds becomes positive) |
| ③ |
When the primary side is turned on, Vds becomes positive → Return to ① |
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| ↓Enlarged waveform |
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②The secondary MOSFET turns off immediately
In most cases, problematic operation of secondary side synchronous rectification
occurs due to loose coupling of the transformer. |
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| File name：2ndSR-solution.pdf |
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To solve secondary side synchronous rectification malfunction caused by transformer coupling. |
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