Diodes synchronous

For those applications where high efficiency is important, synchronous rectification may be used on the higher current (power) outputs. Synchronous rectifier circuits are much more complicated than the passive 2-leaded rectifier circuits. These are power MOSFE B, which are utilized in the reverse conduction direction where the anti-parallel intrinsic diode conducts. The MOSFET is turned on whenever the rectifier is required to conduct, thus reducing the forward voltage drop to less than O.f V. Synchronous rectifiers can be used only when the diode current flows in the forward direction, that is in continuousmode forward converters. 

Synchronous Diode. A Sehottky diode about 30 pereent of the rating of the eon-tinuous rating of the synehronous MOSFET needs to be plaeed in parallel with the MOSFET s intrinsie diode. This would be about 0.66 A at 30 V. I will use an MBRS130. This diode produees a 0.35 V forward voltage drop at 0.66 A. 

The following arguments apply to a Synchronous Buck converter, too (with the Schottky diode placed across the lower Fet), but the effects can be much more severe in a Boost because of the typically higher voltages involved. 

Figure 3-11 Maximizing Efficiency of a Synchronous Boost by Means of a Schottky Diode Connected with Low-inductance Traces...

In one case, I remember that a standard Non-Synchronous Buck switcher IC was not working right. Everything seemed OK, the PCB, the decoupling, and so on. We tried swapping the switcher IC at first, but the problem stayed with that board. Eventually we traced it to the Schottky catch diode. We then discovered that cheap... 

Another milder example of this is a standard Non-Synchronous Buck switcher IC. Every single typical applications diagram on the datasheet shows a Schottky diode, without perhaps explicitly stating as much. This is an example of an implied expectation on the part of the vendor—that you, the customer, won t miss the truly obvious. Yet there are many who think they have achieved some slender advantage in substituting an ultra-fast diode in its place. First read the Abs Max section of the EC tables carefully. Most vendors specify that the SW node should never be taken more than 0.4V below IC ground. That is because... 

To synchronize the fluorescence to the continuous sinusoidal deflection voltage of the streak camera, 10% of the visible output from the dye laser was directed onto a pin photodiode which was used to trigger a tunnel diode oscillator. The output of this oscillator was then frequency... 

Figure i I-6 Use of a diode array in the SYNCHRON CX7 monochromator reduces requirements for moving parts. For simplicity, ray traces for only three wavelengths are shown. (Courtesy Beckman Coulter inc www.beckmancoulter.com.)... 

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