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quality of power supply

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#3
SY said:
How important is a tire?

It's all a matter of what you're trying to do and what your critereon of "best" is. What's perfectly adequate for one situation or application may not be in another. Can you be a bit more specific?
Click to expand...


o.k. sorry.....

is nessesarry to use choke in PS for common CF or can I use transistored version?

and....how do you know, when DC is enough DC to avoid hum?


I'm learning....
 
#4
OK, we're getting closer now. A cathode follower has good power supply rejection, so the B+ quality isn't hyper-critical. How good is good enough? From an engineering perspective (as opposed to unsubstatiated anecdote), it's good enough when the noise/hum/ripple is low enough not to degrade the output signal at a level higher than the desired signal to noise ratio. This should take into account the PS rejection of the CF, which makes things easy.

For example, let's say you're designing a CF to handle signals in the 1V range, and you want the S/N to be better than -80 dB with respect to the 1V reference level. That means that any noise components due to the supply should be 80 dB below 1V. If the CF has a PS rejection ratio of 40 dB, that means that the supply's hum and noise should be 80-40 = 40 dB below 1V, or 10 millivolts for this example.
 
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