Synchronous Rectification

[bogsof]

Have anyone pictures with power source which use Synchronous Rectification for out voltage?
Sorry for my english.

[bogsof]

Re: Synchronous Rectification

You really don't see this or you don't know what is this?
The Synchronous Rectification is made using MOS-fet transistors (in replace of output diodes).

[PeteS in CA]

Re: Synchronous Rectification

Here is a datasheet for a Linear Technology Synchronous Rectifier controller. It has two "typical" application schematics that show how synchronous rectifiers are used in a P/S circuit. There is also a corresponding primary side PWM controller, the LTC1681. You aren't likely to see synchronous rectifiers used in a PC P/S, at this time anyway, as it is more complicated and expensive. usually synchronous rectification is used when efficiency is a premium feature and there are low voltage O/Ps. Because MOSFETs and dual schottky rectifiers use the same packages - TO-220, TO-247, D2PAK, etc. - you probably won't notice an obvious difference between the circuits until you see that there are more "rectifiers" and see that the P/Ns on the parts are of MOSFETs, not rectifiers.

What makes synchronous rectification complicated is timing, timing and ... and ... oh yeah!, timing. If the forward FET doesn't turn on soon enough, its body diode conducts, which works, but hurts the efficiency, may affect low-line performance and generates extra heat. If the Forward FET doesn't turn off soon enough, the Forward FET and Catch FET basically short out the transformer secondary briefly, which hurts efficiency, generates heat and can mess up the control loop (which may think there is a shorted O/P). There are similar issues with turn-on and turn-off timing for the Catch FET. Those timing issues can drive a tech bringing up a new design balmy - BTDT, got the straight jacket!

Hope this helps some.

[japlytic]

Re: Synchronous Rectification

I think synchronous rectifiers would be used in 1KW+ power supplies, especially those designed for servers.

[bogsof]

Re: Synchronous Rectification

First I want to thanks for reply.
This photos is with PC-ATX modify by me for synchronous rectification.
I wanted to see one made industrial.

[gonzo0815]

Re: Synchronous Rectification

I have seen a shematic, probably similar like your changes. There was no need for any extra controler, there are only some extra wires fromm the transformer, to provide gate current at the right pulse. But unfortunately SR is only be good for higher load, whereas efficiency will be lowered if the load isn`t that high. I remeber a suggesteion to bypas the circuit for lower loads.
Any way, if you can provide detailed description, what you have done, i would be glad to se it. This topic has always interested me.

[PeteS in CA]

Re: Synchronous Rectification

There was no need for any extra controler, there are only some extra wires fromm the transformer, to provide gate current at the right pulse.

What I said about timing still applies, as MOSFETs have turn-on and turn-off delays.

[bogsof]

Re: Synchronous Rectification

I will provide some information but not now, and I want some photos or schematics, because I work on this topic from 4 years (is on of my personal project) and I invested too much time and money.
Regarding efficiency: with same load, the temperature of radiator of rectifiers is with 28ºC lower, in same conditions of ventilation.

[bogsof]

Re: Synchronous Rectification

In replay to PeteS in CA:

One suggestion: use for primary switch MOS-transistor and un transformer driver, and in this transformer make wires for secondary MOS rectifier. In this way you can have the same timing, if you select in right way the MOS-transistors in primary and secondary (you will have the same delay).