On 5/28/07, Richard Brewster put forth:
>Mark, why don't you hustle over to the MOTM catalog website and pick up
>that last MOTM-950 kit,
Oh, I don't use power supply modules -- they take up way too much
valuable panel space. Also, the MOTM-950 provides only 400mA of
-15/15+, and it costs way more than putting a similar supply in a
separate box, which I would have to do anyway, to get more -15/15+
current.
>One disadvantage of adding a separate +5V supply is wiring it up. If
>you're cool with that, it is an option.
I already have the MOTM triple-power distribution board, so
wiring it up shouldn't be that difficult.
>But stay away from the switching supplies! You don't want that
>noise near your modular. All my supplies are Power One. These are
>reasonably priced and available from Digikey.
If it is only used for the digital circuitry, does the noise make a
difference?? The reason I ask, is that switching 5V supplies are a
fraction of the price of linear supplies.
>Why did John Blacet use large, multiple, electrolytic caps for
>decoupling? One reason could be that Blacet the modules have a lot of
>chips on them and different sections of circuit that need to be
>isolated. Sometimes it is better to over-engineer. Too much decoupling
>is generally better than not enough. Some drawbacks of using big caps:
>takes up extra space; is a tad more costly; and of course the problem
>with power supply startup.
That's true -- many of the sub-circuits on both of those modules
could be rather noisy. Although it doesn't explain the lack of
smaller (.iuF) caps on the linear IC's or address the issue of noise
at high frequencies. Anyway, I'm considering replacing the two 100uF
caps at the power input with smaller values. I'm thinking that there
shouldn't be that much ripple at the inputs and that the aggregate of
all the 10uF should provide enough of a local current reservoir.
Also, the 100uF caps that came with the Blacet kits are only 16V, and
I wonder if that should be a cause for concern.