Synchronous output rectification and off-line power supply Part I
Did you know you can use synchronous output rectification to achieve high efficiency in a flyback, offline power supply? Many embedded engineers are aware of this. But they don’t apply it in their work.
The best thing about this set up is, it is cost effective and simple to create. The system also comes with an EMI filter to adhere to EMI compliance. The system is perfect for appliances in the range of 12V to 25V. But you can also modify it to apply to devices up to 28V.
In low output applications, conduction loss in a diode rectifier can cause power loss in power supplies including custom power supplies. The conduction loss because of the diode rectifier is in proportion to the product of the forward conduction current and forward voltage drop.
In this situation, you can get better results by using a synchronous rectifier instead of a diode rectifier. In case of a synchronous rectifier, the forward voltage drop is lower compared to a diode rectifier.
Consequently, the conduction loss because of the rectifier is reduced. You don’t need to take our word for it. Many tests have been conducted on this principle and the results are uploaded to the internet.
Note that the work of the self driven synchronous rectifier is dependent on how you reset the power transformer because the synchronous rectifier works around the reset voltage. This technique could have far reaching ramifications for a custom power supply.