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Old 3rd Dec 2018, 5:27 pm   #1
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
Default Reservoir capacitors and ripple current.

If this isn't the relevant discussion forum mods please move it.
Ok, I'm modelling the PSU for a stereo power amp build.
It's for 4 x EL34 with a total current draw around the 300mA mark, this includes the calculated draw for preamp and phase splitter valves.
So far so good, the PSU modelling software gives me 450V across the first reservoir capacitor. Using a standard silicon bridge rectifier rated at 25amps 1kV.
After that it's choke and capacitor smoothed to the CT of the output transformers.
So I was looking at the choices of reservoir capacitor with a high enough working voltage and 105 degC max temp and for pennies more I can get a 470 uF capacitor with a ripple current of 2.15A which seems pretty good.
but I think the ripple current could exceed this value? Am i right in thinking that a higher reservoir capacitance comes at the cost of higher ripple current as the charging pulses will be very high in value?
So what, if any, benefit do I get by increasing reservoir capacitance above say 16uF where the psu model shows a more modest ripple current of about 1.5A as I think if I use anything above 100uF the ripple current goes up to 2,5A or have I made an error in the calculation/interpretation of the simulation software?
There shouldn't be any noticeable hum, the choke and subsequent capacitor and resistance networks to each stage should filter that adequately and I'd expect a reasonably balanced PP output to cancel a lot of PSU hum out.
The transformer is massively over specified and would supply 8 x EL34 if asked so I assume it will be capable on its own of providing a bit extra current on peaks?
I will have made a number of schoolboy errors here I know. I could just run with what I know works but I'm trying to get an understanding of the way a PSU does its thing as part of this DIY project.
Sorry its a long question.
Andy.
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