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Registered Member #6129
Joined: Sun Aug 12 2012, 04:33AM
Location: somewhere downunder
Posts: 7
We put a diode in a power line, it allows movement in one direction only, but it has a voltage drop, is there a way to do the same thing without a voltage drop. Thanks Ernie
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Theoretically NO, as switches of any type have resistance, even if mainly in the connections.
In practice the volt drop loss can be very small by using a transistor switched synchrounously with the ac. Modern low voltage output smps use 'synchronous rectification' with mosfet switches.
Early technology using mechanical switching/comutation controlled by a synchronous motor could do 1/2-wave or full-wave rectification with very low switching losses, as the switchng occurs at zero voltage crossing.
If you are using D.C. then I guess the simplest you can do is to use a low voltage drop rectifier such as a schottky diode. You could have a hall-effect device monitoring the current which switches a transistor in place of the diode, a much lower voltage drop but more complex.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Yup, synchronous rectification. If it wasn't for this, the average PC SMPS would be about the size of a house brick and weigh about the same.
The transformers used run up to around 3 MHz now, and with the Transoner (tm) ones could be made in 120W dual mode units not much bigger than a matchbox yet provide better than Type 2 medical isolation.
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