How Important are Low ESR Capacitors

[Technoguy3]

How important are low ESR capacitors? When is it necessary to use them and why?

[japlytic]

Re: How Important are Low ESR Capacitors

Low-ESR capacitors are essential in switching power supplies (including DC-DC converters).
For the primary side 200/250/350/400/450V unit(s), you can usually get away with a standard (preferably high ripple rating) unit.

[Technoguy3]

Re: How Important are Low ESR Capacitors

What are switching power supplies? When are they used and why?

Thanks! What are primary side units?

[mariushm]

Re: How Important are Low ESR Capacitors

No offense but the questions you're asking are so simple they have answers in Wikipedia and Google.

Electronics often work with low voltage, which is 1.8 , 3.3v, 5v, 12v ... to put it in comparison a simple AA battery has 1.2-1.5v
The socket on the wall in your house has around 110v and in other countries the sockets have 230v

Chips can not handle that much voltage so there has to be a device to convert this 110-230v to those lower voltages in a way that would also make the devices safe for humans.

Transformers take care of the safety factor and they're the main way of obtaining lower voltages from high voltages. You can read about them here: http://en.wikipedia.org/wiki/Transformer

Basically, the "primary" in a power supply is the part of the power supply where there can be high voltage. The secondary side is the part that has only low voltages and safe ones.

So by primary side "units" he meant the capacitors rated for high voltage.

The simplest power supply possible is made out of a transformer and a bridge rectifier which converts the low voltage AC current generated by the transformer into DC voltage.

A switching power supply is a type of power supply that converts high voltage (100-400v) into lower voltages by sending pulses of electricity through a somewhat special transformer.

Depending on how much power is demanded by the devices attached to the power supply, the controller (a kind of basic processor) inside the power supply adjusts the length of those pulses to send more current on the other side.

So several thousand times a second the controller checks how the voltage is on the output and tries as best as it keep to keep it steady by shrinking or extending those pulses of electricity through the transformer.

Capacitors and inductors are used on the secondary side to smooth out the voltages. They have to be Low ESR because put in a very simple way, esr is a propriety of capacitors, something which makes it hard for that controller to work properly and produce good low voltages.

Ideally, you'd want linear power supplies to generate low voltages for the computers. However, this is not possible because the transformers inside the power supply would have to be very big and heavy... think the transformer alone being as large as 2 DVD drives. Switching power supplies are used because it's possible to use special transformers that are small and light.

You can read more about switching power supply here: http://en.wikipedia.org/wiki/Switched-mode_power_supply

And you can read more about all kinds of power supplies, including the simple ones here: http://en.wikipedia.org/wiki/Power_supply

[Technoguy3]

Re: How Important are Low ESR Capacitors

Thanks! I read that Wiki article before and didn't understand a lick of it. But you pretty well answered my questions in a simple paragraph. Wkipedia needs more of the "human element", I think. Will go back and see if I get it now.

[Technoguy3]

Re: How Important are Low ESR Capacitors

What is "impedance ratio"? I keep seeing it on datasheets but it gives me no real info on what the ESR is? How do I know what the ESR is from "impedance ratio"?

Example:

[twbranch]

Re: How Important are Low ESR Capacitors

No offense, but I can change wikipedia in two seconds.

[Technoguy3]

Re: How Important are Low ESR Capacitors

No offense, but I can change wikipedia in two seconds.

The smart people who change Wikipedia typically aren't the ones that read it to gain knowledge.

What is impedance ratio? Anyone?

[mariushm]

Re: How Important are Low ESR Capacitors

It's not a term I'm familiar with but I assume it's about how much impedance changes when the capacitors are working at a temperature different than the one in the rating.

The datasheet says :

Impedance Ratio
ZT/z20 (MAX.)

and you have there :

Rated Voltage(V) 6.3 10 16 25~100 160~250 350 400 
Impedance Ratio
Z-25℃/Z+20℃    4 3 2 2 4 4 6  
Z-40℃/Z+20℃    8 6 6 3 6 8 10 
T/z20 (MAX.)

So that simply means that the at -25c the impedance for a 6.3v capacitor is 4 times the impedance at 20c.
At -40c, the impedance is 3 times the impedance of a 25-100v rated capacitor.

That's just an assumption, like I said, I'm not familiar with the term.

This series of capacitors you linked to is general purpose, it's not Low ESR or specialty, so the impedance and ESR are not important, hence why they're not even listed in the datasheet.

[Technoguy3]

Re: How Important are Low ESR Capacitors

Okay, thanks a lot. so it's a pretty safe assumption That if ESR isn't listed, then it's not a low ESR capacitor.

[twbranch]

Re: How Important are Low ESR Capacitors

The smart people who change Wikipedia typically aren't the ones that read it to gain knowledge.

What is impedance ratio? Anyone?

My point is I have found many things and I mean a lot of things inaccurate on wikipedia. I would not trust that site for info when dealing potential electrical energy. Safety first!

[Andrew4096]

Re: How Important are Low ESR Capacitors

My point is I have found many things and I mean a lot of things inaccurate on Wikipedia. I would not trust that site for info when dealing potential electrical energy. Safety first!

I agree. I've been contributing to Wikipedia for over seven years in all kinds of topics, and I've found it to be a very political environment. Edit wars go on frequently behind the scenes and editors with better ideas and balanced approaches to topics often get driven out or simply leave in disgust. That said, I still use it as an entry point, particularly technical/computer topics, because the articles define terminology and provide links where one can learn more. In that sense sites like Wikipedia are not much different than traditional printed and bound encyclopedias.

[tom66]

Re: How Important are Low ESR Capacitors

My point is I have found many things and I mean a lot of things inaccurate on wikipedia. I would not trust that site for info when dealing potential electrical energy. Safety first!

Wikipedia is very useful for electronics engineering, including theory and practical elements. It can be inaccurate, but so can reference manuals and books. Unlike reference manuals and books, it can be corrected essentially instantly.

The most important rule with electronics is to take care and understand the risks. No internet article should be trusted with this.