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LT4320 active rectifier
LT4320 active rectifier
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Old 23rd August 2013, 04:39 PM   #1
Conrad Hoffman is offline Conrad Hoffman  United States
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Default LT4320 active rectifier

I just thought the new ideal diode bridge controller was the bee's knees. Thoughts?
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Old 23rd August 2013, 05:23 PM   #2
peranders is offline peranders  Sweden
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LT4320 active rectifier
This was surprising, cool chip.
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Old 27th August 2013, 03:33 PM   #3
davidsrsb is offline davidsrsb  Malaysia
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More useful for low supply rail class A, where rectifier efficiency is usually lower
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Old 19th October 2013, 04:00 PM   #4
crt is offline crt  Indonesia
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Just try it
18VAC with no load i got 24,09VDC, with MUR1560 i got 23,18VDC

what i hate is the package of IC, its very small to my eye
and mess up soldering all the board
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Old 21st October 2013, 03:34 AM   #5
Damon Hill is offline Damon Hill  United States
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Interesting. I wonder how well MOSFETs do as low-EMI/RFI devices in rectification? Over-voltage/spike protection would seem essential, as a TVS is recommended.
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Old 21st October 2013, 10:41 PM   #6
Refugee1 is offline Refugee1  United Kingdom
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There should be no problem with over voltage once a big capacitor is connected across the DC end of it. The spike will just get shoved into the capacitor and if a film capacitor is also added across the main smoother it will look like a short up to the peak pulse currant the FET can take. They should run cool as the volt drop across the FET will be less than a diode at normal working load.
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Old 22nd October 2013, 12:15 AM   #7
Johno is offline Johno  Australia
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LT4320 active rectifier
Not sure if suitable for power ampl supplies.
The rectifier fets must have the same ratings and similar specs as the output fets or transistors of course.
Same SOA and heatsinking too.
If the outputs are paralleled then the rectifier ditto.
If the outputs have drivers then the rectifier ditto.
That is, it is not going to scale upwards nicely or simply or more economically. In fact I have never heard of a problem of heat in those 25A metal case bridge rectifiers that we tend to use, so why bother?

And for low current applications, also why bother?
If you need extra output voltage it is much easier to add another 5 turns of secondary winding or use low forward drop diodes or select the correct transformer in the first place.
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Old 22nd October 2013, 04:21 AM   #8
crt is offline crt  Indonesia
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Quote:
Originally Posted by Johno View Post
Same SOA and heatsinking too.
NOPE, it does not need any heatsink

it much COOLER than normal MUR1560 rectifier that i use for F5 (with heatsink)
41 Deg Celcius vs 73 deg Celcius (with 1.4 A each channel BIAS) ==> it means a lot to me
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Old 22nd October 2013, 07:28 AM   #9
Johno is offline Johno  Australia
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LT4320 active rectifier
That photo is impressive.

So about heat. My logic was that the RMS current consumed by the amp, including the output, is the same RMS current that flows in the rectifying fets or diodes for that matter. Thinking about it, I did not take enough consideration of the mode, the rectifier is either fully on or fully off, the outputs are linear. Oops!

However my negative feeling about complexity remains.
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Old 22nd October 2013, 11:50 AM   #10
Refugee1 is offline Refugee1  United Kingdom
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The theory is that a diode will be heated by working currant multiplied by forward voltage in watts.
A FET driven by a square wave from the chip will be heated by the currant multiplied by itself and then by the on resistance.
The on resistance of FETs is getting lower every time a new part number is issued. These things now pay for themselves quickly in power savings.
Take a FET with an on resistance of 0.1 ohms and blast it with 10 amps. It will be heated by 1 what.
Take a power diode with a forward voltage of 0.6 volts and blast that with 10 amps and you get 6 whats of heat.
Do have a look at the data sheets in order to work out the power consumption of the parts you have already got.
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