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LT4320 based active rectifier

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prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
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DaveFred said:
I have read the stuffing guide, studied the schematic and have been reading as much as I can about power supplies to try and not ask too dumb a newbie question.

What are the variables in the schematic that need to be adjusted for different sized/voltage transformers?

Lets assume a 300VA 35v dual secondary transformer.

To me it looks like,

- the obvious, the big main caps (C1..C4) have to be the correct voltage (i.e. 63v caps for 35v transformer)
- snubbers (CX, CS, RS) based quasimodo jig, or left out if using your LT4320 based active rectifier
- LED resistor (R10, R11), based on transformer voltage

My questions are about,

- the filter resistors, R1..R6 or RP1, RP2, it looks like it you use R or RP, but not both, when would you use one vs. the other, and how do you pick the values? R1..R6 are shown to be 1 ohm, is that a fixed value or does it change based on transformer? How many watt should they be and of what type? RP1, RP2 are shown as type BPR 56 5 watt resistors, but what value should they be if used rather than R1..R6?

- the Vishay PB3506, for what sized and voltage transformer are they good til? If and when would you need to go to PB3508 or PB3510?

- R8 and R9 are shown as 1 ohm 1 watt resistors, does the type matter?

- RB and RB' are shown as typical value being 2200 ohms, 3W for 35 volts. Is that typical for a 35v AC transformer or a rectified DC voltage of 35v?

- For the ground pad between the bulk caps, I looked around the Elliot Sound Products web site and didn't find the information about for connecting it to the chassis via a disconnect network, I thought this search would have worked "disconnect network" site:Elliott Sound Products - The Audio Pages (Main Index) . Does anyone have any direct links where I can read specifically about his?

Sorry for such basic questions.

David.
Click to expand...

Hi Dave somehow i missed your post.
here are answers.
Use either R1-R6 or RP1/RP2. effective resistance about 0.1 ohm to 0.33 ohm is a good value for crc type supply.
for 35v secondaries, PB3506 OR PB3508/PB3510 are good. but will need heatsink depending on current demanded from your amp. e.g. for 5 amps, voltage drop in rectifier is ~1.0v , so power dissipated is approx 5W.
for class ab amp and normal listening, you could do away without heatsink.
Blocked

chassis discoonect network ... Power Supply for Power Amplifiers or some use a cl-60 between psu ground and chassis.

RB and RB- you can use 3300ohm also, its not critical. it determines how fast your caps are discharged when powered down.
 
prasi

prasi

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Joined 2014
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D

DaveFred

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prasi said:
I meant to say, when you use lt4320, you can do without the snubbers. i have given the option of use of snubbers based on some member's request

with normal rectifiers + if you have quasimodo jig, then you can determine the value of snubbers and use them.

Simple, no-math transformer snubber using Quasimodo test-jig
Click to expand...


Since I was asking about CS, CX and RS on both boards,

I understand that CS, CX and RS should/can be used on the Compt-CRC board if used by itself with a standard rectifier, using the values from the Quasimodo jig (I have one).

I also understand that if using the LT4320 board, not to use CS, CX and RS on the Compt-CRC PSU board.

I was wondering about if CS, CX and RS should be used on the LT4320 board itself?

LT4320 board.jpg

I may have answered my own question (don't use them) as I don't see CS, CX and RS on a later version of the board (just noticed that).

Thank you for your patience!

David.
 
prasi

prasi

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1. In later version (latest) of tht lt4320 pcb, the option is still present with smd snubbers on bottom.

2. in smd lt4320(latest) pcb, i have removed it because if someone wants to experiment, he will use them on his main caps psu pcb(e.g. compact crc that you had originally asked about). because this smd rectifier pcb will be used as a plugin rectifier with some other bulk cap pcb like the compact crc psu pcb with pb35xx rectifier footprint

3. in the tht lt4320 crc psu pcb that is offered via gb, snubber option is present....

so in summary for you, dont use the snubbers initially... if you feel up to it, you may experiment to any extent with the options provided....
 
Last edited:
M

Macrom

Member
Joined 2003
OnSemi NVMFS5C646

Hi Prasi,

what is the maximum output voltage when using 60Vdss MOSFETs?

Can I use them up to 50V or do I need to consider a bigger headroom?

I have some of the OnSemi NMOS NVMFS5C646 left.
Any idea if they might work with the LT4320?

Thanks in advance for your feedback.

BR,
Macrom
 
W

wgh52

Member
Joined 2011
Hi Macrom,

Vdsmax of 60V is the "Drain-Source breakdown voltage", beyond which the device would probably be damaged. The max. recommended supply Voltage for the LT4320 is 72V (absolute max. before damage is 80V). This is all derived from the respective datasheets an suggests to me that your "50V project" is most probably "safe".

Regards,
Winfried
PS: Schöne Grüße ins schöne Frankenland!
 
Last edited:
prasi

prasi

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Joined 2014
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Hello all,
Since i had run out of THT lt4320 rectifier, I had ordered few more.
Now I have 48 pairs of tht lt4320 boards in addition to remaining lt4320 crc psu and smd lt4320 rectifier boards.
If someone needs any , pl let me know..
I have updated the google sheet to reflect available stock.

LT4320 RECTIFIER AND LT4320 CRC PSU GROUP BUY - Google Sheets

regards
prasi
 
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