F5X -- the EUVL Approach - The Build Thread - Page 62 - diyAudio
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Old 16th June 2013, 12:53 AM   #611
alazira is offline alazira  United States
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Hi,
Can someone advise me on how to calculate the power requirements for the bridge diodes in this amp? I have some 15A rated ones I would like to use but want to know if it will be sufficient.
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Old 16th June 2013, 04:03 AM   #612
EUVL is offline EUVL  Europe
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Yes, 15A is sufficient.
What is the part number ?


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Old 18th June 2013, 12:52 AM   #613
Horio is offline Horio  United States
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Not bad for an amateur SMD guy:

Click the image to open in full size.

Click the image to open in full size.

Good liquid flux, tweezers and braid really helps.
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Old 18th June 2013, 12:54 AM   #614
EUVL is offline EUVL  Europe
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Excellent.


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Old 18th June 2013, 01:35 AM   #615
alazira is offline alazira  United States
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Quote:
Originally Posted by EUVL View Post
Yes, 15A is sufficient.
What is the part number ?


Patrick
VS-15ETH06FPPBF

VS-15ETH06FPPBF Vishay Semiconductors | Mouser

http://www.mouser.com/ds/2/427/15eth06p-87399.pdf

There is a 30A version, but it doesn't come in an isolated tab package.
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Old 18th June 2013, 01:46 AM   #616
EUVL is offline EUVL  Europe
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Specs looks OK. Should work.


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Old 26th June 2013, 11:05 AM   #617
ramallo is online now ramallo  Europe
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Hi Patrick,

Finally with full load the voltage after CRC is 18.1V.

A dumb question, I don't have clear what is the right polarisation current per device. Now I have 333mV across the 0R22 resistor (Measured after two hours) (1.5A per device / 6A per channel). I read on the thread that the right value is 2A per mosfet. But with 1,5A my amp is hotter than hell . (6 seconds by hand test, ambient temperature 32 C) (The top panel is much hotter that the heatsinks).

Am I wrong?

Thanks!


Quote:
Originally Posted by EUVL View Post
> Before CRC = 21,4V

That is OK.

> After CRC = 19,8V

Difference before and after CRC is 1.6V.
R in the CRC is 0.67R.
So your total bias per balanced F5X is at this moment 2.4A.
Dissipation per FET is 24W per FET, so nothing detrimental will happen.

For optimum output at 6 ohm load, total bias current per channel should be 4A when fully warmed up.
Suggest you check voltage across the 0R22 resistors on the F5X PCB.
To be on the safe side you can start with cold bias (room temperature) of 1.5A.
That means voltage across the 0R22's should be all 0.33V at start up.

And please read Dave's excellent instructions at the start of the thread.


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Old 26th June 2013, 12:09 PM   #618
AndrewT is offline AndrewT  Scotland
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two times 1.5A does not equal 6A.

What have you built?
What bias have you used?
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Old 26th June 2013, 12:23 PM   #619
ramallo is online now ramallo  Europe
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Quote:
Originally Posted by AndrewT View Post
two times 1.5A does not equal 6A.

What have you built?
What bias have you used?
I'm sorry, I probably would not have explained well. I left every mosfet at 1.5A, 333mV across the 0R22 resistor. 4x 1.5A per channel (A F5X channel have 4 x fets, two for F5 side) Am I wrong?
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Old 26th June 2013, 12:41 PM   #620
AndrewT is offline AndrewT  Scotland
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Wrong.
The bias current passes through both mosfets on one side in series.
It's the same current in the N & P fets.

The other side does the same.
That way your total bias for the two halves of the balanced amplifier is two times 1.5A = 3A of bias current.

If you now add the right and left channels toether you will have the PSU supplying a total current of 6A IF you only had ONE transformer.

Each transformer supplies 3A.

In a standard F5X build the current is 4A.
All the fets were measured and selected for this 4A of current (2A through each FET).
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