'Ripple' Current vs 'Ripple' voltage - Page 1
Forum section: electronics / projects

author: jaunty
author_rank: Regular Contributor
timestamp: December 21, 2018, 04:03:02 am
content: okay -so here's a bit of a technical question ... or maybe an abstract one ...I KNOW the term 'ripple current' is generally associated with capacitor spec'ing etc ...but earlier i got into a bit of an argument with someone over use of the term 'ripple current' in relation to talking about how well regulators work in a power supply and how i must be some kind of idiot or jerk for using the term ... they seemed quite offended at any rate. SO - i thought i'd ask. I mean - voltage and current really aren't THAT separable are they - they are both simply a different manifestation or measurement of the same electron flow - no? if you've got a measured ripple in voltage then wouldn't you also have a 'ripple' in measured current too? where should the terms be used or not used then?

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2018, 05:36:17 am
content: Ripple current is what you get when you push a rippling voltage into a load. It's no different than the way current is what happens when you have voltage feeding a load.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 21, 2018, 06:01:14 am
content: The terms are pretty self-explanatory if you understand the concepts of current and voltage, aren't they?Ripple current is the AC part of the current in a supposedly DC current system. Ripple voltage is the AC part of the voltage in a supposedly DC voltage system.For avoltagesource, thevoltageripple spec is important, since that's what's claimed to be regulated. Current ripple would vary massively depending on the load.For acurrentsource, the current ripple spec is important, for the same reason.Note that internally, they lead to each other. For example, many switch mode topologies aredesignedaround having a massive (around 30% of the maximum output current) ripple current in the inductor. The output capacitor equivalent series resistance (> 0) converts that current ripple to unwanted voltage ripple by standard Ohm's law.(AC) ripple current is a relevant spec for a capacitor, since only AC current flows in capacitor, causing resistive heating (I^2 * R), shortening the lifetime. You can, of course, give a AC voltage rating for the capacitor as well, since a specific AC voltage waveform would generate a specific AC current waveform, causing the same heating. This is a simple conversion calculation. Depends on the intended application which one (or both) are given in the datasheet.Maybe you used a funny wording in your argument? Some people are extremely pedantic and expect the "standard" way of expression, like they learned it from a book. I don't think this is the best way, even when they are right, and even if I were wrong. A fresh look from a different angle, using nontypical terminology to express the same, helps learning and understanding, and is more important than who's technically right.

author: jaunty
author_rank: Regular Contributor
timestamp: December 21, 2018, 10:37:12 pm
content: thanks for the 'splaining ... yes i'm sort of constantly using different terms for things and 'trying out' lexical variations so i suppose i shouldn't be at all surprised when it happens ... electronics is very tricky for creativity however - i mean it's complicated enough just looking at things in a sort of 'status quo' way and figuring out what was going on ... i'm always driving myself nuts thinking of stuff like 'what if signal were to flow THIS WAY - backwards through and inductor say or be induced on this track - what then? gahhhactually -total logical jump here ... i was thinking of starting a topic here about pitfalls to learning - misunderstandings that we may have been under for a long time that hampered learning ... i certainly have more than my fair share! the forum has been great for helping with that stuff though

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 22, 2018, 03:03:46 pm
content: Ripple current through a capacitor is what heats it up and shortens the life. It's very hard to calculate and is best measured. Ripple voltage from a regulator or power supply may feed through downstream circuits, causing hum in audio systems or other problems. It's usually measured as a voltage. Obviously voltage and current go hand in hand, but often one is more illuminating than the other in understanding a circuit.