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LT4320 based active rectifier
LT4320 based active rectifier
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Old 21st April 2019, 06:36 PM   #11
xrk971 is offline xrk971  United States
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LT4320 based active rectifier
I am running into the same situation in making an all TH PSU using the active bridge.

The use of TH components requires double the parts and the parts are large.

Here is an example of a 10A capable active bridge (just one rail):
Click the image to open in full size.

Here is the layout for the TH equivalent (dual rail) - it takes up 20% of the real estate whereas the SMT version is a small fraction of that and can be mounted on underside:
Click the image to open in full size.
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Old 21st April 2019, 07:53 PM   #12
Lo_Tse is offline Lo_Tse  Canada
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Quote:
Originally Posted by prasi View Post
1. minimal power dissipation, no heatsink for rectifier, higher DC voltage output for a given AC voltage, etc

2. yes, it is a drop in replacement for SIP-4 type rectifiers.

3. THT option for LT4320 provided, MOSFETs are SMD, but will be simple to solder for anyone who has soldered SMD's before.

regards
Prasi
Yeah, the dual MOSFET is about the size of a smd opamp. Soldering should not be too bad. Using solder paste to stick the component to the board will help if you do not want to use regular solder. I prefer to use screw connectors than pins for AC though. Just curious what is the estimate of the current limit of the smd MOSFET. Thanks!

I have to agree with X and Prasi, using all TH components will increase the size (and cost) significantly. The 4320 is pretty expensive already

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Old 21st April 2019, 09:24 PM   #13
xrk971 is offline xrk971  United States
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A Vishay-Siliconex SQJQ910EL (pictured above in the SMT implementation), can handle 70A, and up to 175C. Rdson of 8.6mOhm

https://www.mouser.com/datasheet/2/4...el-1110892.pdf

Ohmic heating = 70A^2 x 0.0086ohm = 42W (within rating for part of 62W to 187W depending on how cool you keep it).

For use on a PCB with just conduction to the PCB for cooling I would try to keep under 3W of dissipation. That's about 19A.

These are tough little MOSFETs.
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Old 21st April 2019, 11:03 PM   #14
Lo_Tse is offline Lo_Tse  Canada
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Thanks! X

Indeed, these are "powerful" MOSFET. You are talking about the smd version, right? Come to think about it, the size of the smd version of the MOSFET is only about 5 x 6 mm, 3 W dissipation is a lot for such a small device (please correct me if I am wrong) and there is no cooling. Is that OK?
However, I suspect that the typical current draw (for a class A amp running at 30 V) is probably under 5 A. So, the heat generated will be much lower.

Looking forward to your testing results!!

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Old 22nd April 2019, 12:40 AM   #15
xrk971 is offline xrk971  United States
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At 4.35A they don’t even get warm. Direct cooling to PCB as heatsink can dissipate 1W to 2 mE no problem if there is more copper and vias to conduct heat away.
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Old 22nd April 2019, 01:21 AM   #16
Lo_Tse is offline Lo_Tse  Canada
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Great!! Thank you for the information. Good to know that!

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Old 22nd April 2019, 02:06 PM   #17
prasi is offline prasi  India
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LT4320 based active rectifier
Quote:
Originally Posted by gary s View Post
Hi prasi, do you think there would be more demand for your PCB if you made it using through hole components rather than SMT devices.

I assume you are trying to make it as small as possible.
Here is my all THT version of the rectifier, though small enough, its still cant replace the SIP-4 type rectifiers.

regards
Prasi
Attached Images
File Type: png LT4320-TO220-THT-LAY.png (48.8 KB, 408 views)
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Old 22nd April 2019, 02:19 PM   #18
xrk971 is offline xrk971  United States
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Nice TH layout, Prasi. Still, a very handy circuit to have on hand.
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Old 22nd April 2019, 11:37 PM   #19
Lo_Tse is offline Lo_Tse  Canada
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Quote:
Originally Posted by prasi View Post
Here is my all THT version of the rectifier, though small enough, its still cant replace the SIP-4 type rectifiers.

regards
Prasi
Hi, Prasi

Looks good! Just curious, are there any special reasons that you put 2 "diode bridge" together on one PCB?

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Old 22nd April 2019, 11:53 PM   #20
prasi is offline prasi  India
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Hi Lo,
to make either +/0/- voltage by connecting in series or to get 2 V+ voltages.
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