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Old 26th April 2007, 01:46 PM   #491
cviller is offline cviller  Denmark
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You'll find the truth in the details!
http://www.diyaudio.com/forums/attac...amp=1175113176

The 250mV is correct.
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Old 26th April 2007, 02:00 PM   #492
cviller is offline cviller  Denmark
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Quote:
Originally posted by lykkedk
I am just preparing a setup for matching mosfets... Se this LINK

So i would just like to know the voltage / current, for correct matching. (And to test the heatdissapation too)

Jesper
About the matching, unless you let your devices reach temperature equilibrium, the timing is crucial. You need to run the devices for the same amount of time. I doubt it will be a good idea to use a heatsink, since it will take ages to heat up and make it harder for you to ensure consistency in your measurements.
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Old 26th April 2007, 02:12 PM   #493
lykkedk is offline lykkedk  Denmark
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CViller.

I would like to try something out, about the heatdissapation About the matching i know that i will have to wait the same time every mosfet.

But I am still not getting this clear If 250mV is flowing through the 0,47ohm resistor it sure gives the 500mA, but then if the mosfet is run at 10v it's only about 50w each, is that right ? Sorry i can't see this as easy as you can
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Old 26th April 2007, 02:17 PM   #494
cviller is offline cviller  Denmark
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Quote:
Originally posted by lykkedk

But I am still not getting this clear If 250mV is flowing through the 0,47ohm resistor it sure gives the 500mA, but then if the mosfet is run at 10v it's only about 50w each, is that right ? Sorry i can't see this as easy as you can
You have 3 N-channels each running at 0.5A and 22.75V and the same goes for the P-channel devices. (If you have 23V rails)

Does that answer your question?
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Old 26th April 2007, 02:22 PM   #495
steenoe is offline steenoe  Denmark
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Quote:
Originally posted by lykkedk
CViller.

I would like to try something out, about the heatdissapation About the matching i know that i will have to wait the same time every mosfet.

But I am still not getting this clear If 250mV is flowing through the 0,47ohm resistor it sure gives the 500mA, but then if the mosfet is run at 10v it's only about 50w each, is that right ? Sorry i can't see this as easy as you can
Jesper, the 10V is the value that the smaller fets are matched with (IRF610). Usually the 240's are matched at around 13-15V. You can choose to match them at 0,5A if you like, just adjust the series resistor accordingly. This would be closer to real life for Fet's, sitting in a F4.

Steen
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Old 26th April 2007, 02:33 PM   #496
lykkedk is offline lykkedk  Denmark
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Yes, tnanx Cviller, but i throught they was run at 10v each...

Well thats gives me a 11watt heatdissapation continuesly. My setup is with a 10ohm resistor which gives about 22watt running at 15v, is it ok, to lover the voltage to e.g 11v when matching, for getting about 11watt ?
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Old 26th April 2007, 02:55 PM   #497
cviller is offline cviller  Denmark
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Quote:
Originally posted by lykkedk
is it ok, to lover the voltage to e.g 11v when matching, for getting about 11watt ?
Sure it is. What you do is you find a suitable psu with a voltage X and your transistor will take about 4V from that and the you find the needed series resitance R to get the correct current Y.

R=(X-4V)/Y

In your case:

R=(11V-4V)/0.5A = 14ohm
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Old 26th April 2007, 03:18 PM   #498
lykkedk is offline lykkedk  Denmark
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Cool guy the Cviller Nice to have you around btw.
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Old 26th April 2007, 04:17 PM   #499
lykkedk is offline lykkedk  Denmark
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I tried to make an experiment, with some 'U' shaped 230x50x50x4 Alu. profiles.

The output voltage from a 5A PSU is 12.65, when loaded.
The Series resistor is 9,5Ohm which gives me 12,65v-4v / 9,5Ohm = 0,9A load for the mosfet.
The series resistor swallow 6v and gives the resistor a load of 6v / 9,5Ohm = 0,63A, which is not important in this case...

Please tell me, if i am wrong here
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Old 26th April 2007, 05:21 PM   #500
Darry is offline Darry  France
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Hello,

There is a little difference between the 2 schematics of the F4 amplifier.

On the first version the input is on R1.
On the R0 version, the input is to the connection of R1 and R2.

Where is the truth ?

Darry
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