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Old 3rd Dec 2018, 6:10 pm   #2
kalee20
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Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,059
Default Re: reservoir capacitors and ripple current

Quote:
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?
Adding more capacitance will always increase ripple current.

However, it could well be that the things which determine ripple current are already dominated by series resistance (such as transformer winding resistance), in which case increasing capacitance will hardly make much difference. Modelling will show you if this is true.

More capacitance will give you less ripple voltage. You can make this as low as you like by increasing capacitance sufficiently.

More capacitance also means a bigger can, so more surface area to radiate heat and keep cool.

More capacitance (mainly smoothing rather than reservoir) also means the HT rail is more 'solid' at low frequencies - you are less likely to have trouble with motorboating.

However, more capacitance means the thing takes longer to charge. If you use a kilofarad's worth of capacitance, you will blow your mains fuses every time you try to switch on. This will be even worse if you have a massively over-specified mains transformer, with really low winding resistances. Sometimes bigger ain't necessarily better!
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