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Bridged Amplifier Capacitor Ripple Current

In the same way that we have easy conversions for dealing with sine
waves such as RMS Current = I peak / SQRT(2) and I ave = 2 * Ipeak /
PI, I would like to know if anyone can help with this question;

Consider two bridged class B (single supply) amplifiers driving a
load, the load is connected between each amplifiers output. The power
supply is fed through a large inductor into a large reservoir
capacitor.

For the sake of argument lets say the peak output current is 4 Amps.
This makes the average current 4 x 2 / PI Amps, and this is the
[constant] current in the inductor. The ripple current in the
capacitor is the difference between this average current and the
instantaneous current being supplied into the load. I get the RMS
ripple current as 0.31 Ipeak (using a spreadsheet) but am not sure how
to do the maths to get this answer. Can anyone help?
 
E

Eeyore

Jan 1, 1970
0
Consider two bridged class B (single supply) amplifiers driving a
load, the load is connected between each amplifiers output. The power
supply is fed through a large inductor into a large reservoir
capacitor.

You're using a switchmode power supply ?

Graham
 
E

Eliot

Jan 1, 1970
0
You're using a switchmode power supply ?

Graham

I'm not sure what you are getting at - the inductor is "large" and so
carries a constant current.
 
E

Eeyore

Jan 1, 1970
0
Eliot said:
I'm not sure what you are getting at

I'm asking a question is what I'm getting at, because I haven't seen such a
power supply ever for an audio amplifier.

- the inductor is "large" and so carries a constant current.

It'll have to be very large indeed for that.

Is this some hypothetical scenario ? It doesn't sound like a real world one.

Graham
 
E

Eliot

Jan 1, 1970
0
I'm asking a question is what I'm getting at, because I haven't seen sucha
power supply ever for an audio amplifier.


It'll have to be very large indeed for that.

Is this some hypothetical scenario ? It doesn't sound like a real world one.

Graham

It is real world. It's an RF amplifier. By "large" I mean the
inductor has a value so the current barely changes over 1 cycle. It's
µH's.
 
E

Eeyore

Jan 1, 1970
0
Eliot said:
It is real world. It's an RF amplifier. By "large" I mean the
inductor has a value so the current barely changes over 1 cycle. It's
µH's.

If it's that large then surely there'll be next to no ripple current in the caps.

Graham
 
E

Eliot

Jan 1, 1970
0
If it's that large then surely there'll be next to no ripple current in the caps.

Graham- Hide quoted text -

- Show quoted text -

I think you have misunderstood this somewhat;
The inductor supplies the average current,
The load current varies,
The capacitor supplies the difference between the load current and the
average current, hence the current may be current flowing in or out of
the capacitor. The RMS current in the capacitor is 0.31 * peak load
current
 
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