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Old 13th November 2017, 03:46 PM   #1291
AnthonyA is offline AnthonyA
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Got it. Thank you
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Old 26th November 2017, 05:19 PM   #1292
pistollero is online now pistollero  Portugal
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Hello, how much capacitance can i put after reflector d? On the vref of a dac?
I put 470 uf maximum... can i put more?
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Old 27th November 2017, 12:53 AM   #1293
sbelyo is offline sbelyo  United States
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Originally Posted by Salas View Post
The dissipation of that Fairchild will be the same of that IRF. Because the voltage drop and the current in the circuit dictate that. Its just that the Fairchild will be safer on a pushed current and small sink situation because it has better θjc i.e. transfers heat from its core to its case mounted at the sink more efficiently than the IRF. Safer, but up to a point of course. For more on thermal design basics this is a good read: http://www.analog.com/media/en/train...als/MT-093.pdf
If I use the Fairchild FQP3P20-ND and use large external heatsinks I should be ok if I set it for 800mah ? I would use aluminum angle iron mounted to bottom of aluminum case with the heat sink mounted to the angle iron.
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Old 27th November 2017, 01:33 AM   #1294
Salas is offline Salas  Greece
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Yes it will do OK like that.
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Old 27th November 2017, 01:43 AM   #1295
Salas is offline Salas  Greece
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Originally Posted by pistollero View Post
Hello, how much capacitance can i put after reflector d? On the vref of a dac?
I put 470 uf maximum... can i put more?
You can even put more than 1000uF after it. It won't make it oscillate. But when it hangs directly from the rail without a series R to make RC it goofs up the reg. Reduces its open loop gain i.e. its control is getting lower and the direct to output capacitor's passive filtering role dominates.
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Old 27th November 2017, 12:51 PM   #1296
pistollero is online now pistollero  Portugal
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Originally Posted by Salas View Post
You can even put more than 1000uF after it. It won't make it oscillate. But when it hangs directly from the rail without a series R to make RC it goofs up the reg. Reduces its open loop gain i.e. its control is getting lower and the direct to output capacitor's passive filtering role dominates.
Thanks Salas for the explanation. Thatīs why i tested different caps with different values and combinations and they all sound different after reflektor.
So for the vref of a dac i can have this 3 possibilities..

1 - direct reflektor without any caps (as close as possible to the chip pins)
2 - reflektor and the usually decoupling caps after it...
3 - reflektor and series rc after...

are those correct???
if i use rc after the reflekor, i just need a resistor in series after the reflektor before the first cap? it will drop the voltage? what is the advantage of this?
or is better no caps and only reflektor direct to the pins..
what is your opinion on this??

i tested 3.3v on vref of a simple pcm5122 dac.. i find that reflektor improves the sound...so in my subjective experiences this is the second dac that with reflektor plays better on vref side. when i have more boards i will test on digital side and clocks...
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Old 27th November 2017, 01:50 PM   #1297
AndrewT is offline AndrewT  Scotland
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If the PSU is affecting the DAC performance, maybe some of the solution is in improving the local supply rail decoupling?
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Old 27th November 2017, 09:38 PM   #1298
Salas is offline Salas  Greece
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Quote:
Originally Posted by pistollero View Post
Thanks Salas for the explanation. Thatīs why i tested different caps with different values and combinations and they all sound different after reflektor.
So for the vref of a dac i can have this 3 possibilities..

1 - direct reflektor without any caps (as close as possible to the chip pins)
2 - reflektor and the usually decoupling caps after it...
3 - reflektor and series rc after...

are those correct???
if i use rc after the reflekor, i just need a resistor in series after the reflektor before the first cap? it will drop the voltage? what is the advantage of this?
or is better no caps and only reflektor direct to the pins..
what is your opinion on this??

i tested 3.3v on vref of a simple pcm5122 dac.. i find that reflektor improves the sound...so in my subjective experiences this is the second dac that with reflektor plays better on vref side. when i have more boards i will test on digital side and clocks...
Any regulator followed directly by much capacitance will gradually be dominated by it as its value becomes larger. The Reflektor has some favorable characteristics to you that you are likely trying to preserve. So...

(1) Is best if its so physically close that good decoupling can be preserved without penalty.
(2) Is usually the most practical.
(3) RC "buffers" the following big capacitor from the reg, so it messes less with its characteristics, and also creates a better local filter.

For RC the higher the resistor the better the "buffering" and the RC time longer so the filter is better. Voltage drop is naturally I*R. So if the local mA consumption is limited and the local target voltage minimum can still be served don't be afraid to up the resistor. Start with 10R.
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