In power supplies, every discussion I've seen of electrolytics focuses on good performing caps with low ESR and hi ripple. However, the electrolytics that come after a voltage regulator are often NOT recommended to have low ESR. So what are recommendations of good electrolytic caps that are not low impedance/low ESR, especially in a linear power supply and are not esoteric audiophile types?
I suspect as long as the initial rectification filter cap typically has high current ripple at mains frequency, then low ESR means less heating effect in the cap.
After the voltage regulator - is it because of the stability of the voltage regulator? It's funny because most devices have a solid state film/poly cap to decouple the power. I'd have thought a large capacitance after the voltage regulation simply means the regulator feedback mechanism ends up being impacted and slower to track. Low ESR after be regulator? well alot of regulators have ceramics on the output.
After the voltage regulator - is it because of the stability of the voltage regulator? It's funny because most devices have a solid state film/poly cap to decouple the power. I'd have thought a large capacitance after the voltage regulation simply means the regulator feedback mechanism ends up being impacted and slower to track. Low ESR after be regulator? well alot of regulators have ceramics on the output.
Under some conditions like a chip regulator with built-in protection being used for a large voltage in/out differential latching up into protect mode at start up if the load capacitance is too much.
Mike
Mike
A capacitor at the output of a regulator creates a pole. Enough capacitance may cause the regulator to oscillate.
This can be remedied by adding a small resistor between the regulator and capacitor. The load will still see low impedance at high frequencies due to the capacitor.
Ed
This can be remedied by adding a small resistor between the regulator and capacitor. The load will still see low impedance at high frequencies due to the capacitor.
Ed
Yes ceramics (MLCC) or tantalums are often used to protect the stability of the regulator, but sometimes a variable regulator had an adjust resistor and soemtimes recommended a small cap along with it. I've also read of a couple people who did sims or measurements finding that a 330-560uF cap afterwards helped the performance of the circuit. Because ESR needed to not be too low it was often paried with a Wima film.
If a smallish film cap was soldered across the pins of the electrolytic, would that have a different effect than directly following it on the PCB?
Is your discussion meant to imply that because MLCC and tantalums etc address stability issues, that electrolytics are mostly wanting low impedance/low ESR and no need for electrolytics that are not? If there is cause otherwise, I'd be interested to know of recommended cap series.
If a smallish film cap was soldered across the pins of the electrolytic, would that have a different effect than directly following it on the PCB?
Is your discussion meant to imply that because MLCC and tantalums etc address stability issues, that electrolytics are mostly wanting low impedance/low ESR and no need for electrolytics that are not? If there is cause otherwise, I'd be interested to know of recommended cap series.
A small tantalum or ceramic capacitor should be added to provide a low-impedance path at high frequencies. The regulator's feedback loop becomes ineffective at high frequencies.
A large capacitor (>10uF) should never be added because the regulator's feedback loop already provides low output impedance at low frequencies, and the regulator may not be stable. This is the same consideration as with power amplifiers.
Ed
A large capacitor (>10uF) should never be added because the regulator's feedback loop already provides low output impedance at low frequencies, and the regulator may not be stable. This is the same consideration as with power amplifiers.
Ed
I've used "normal" Panasonics, FR for example, or CDE I'll use for passive RC filters for audio frequencies. Only time I've seen a really large load (IIRC 22uF was a tantalum on a 3080 regulator to give a nice stable output) but it's not the only filter. I've used inductors to give 600R at 24MHz+ ranges provide some impedance for cleaning clocking supplies and decoupling close to the chips etc.
Once you start going fancy - poly hybrids etc (Panasonic AZA etc) then although you'll get low ESR 4000mA current, look at the derating for lower frequencies such as 50Hz and you're multiplying by 0.1. I have those on my pre-amp section sat next to me.. however I know that a better modern power supply for the pre would clear up more noise for the opamps.
Did you have any specific frequency in mind (most regulators such as LDOs drop off over 1MHz)?
As said (and I forgot) - adding additional capacitors in parallel complicates things a little, you end up with multiple poles. I'm not an expert but for the most part - decoupling is better done as close to the device creating the power noise.
Once you start going fancy - poly hybrids etc (Panasonic AZA etc) then although you'll get low ESR 4000mA current, look at the derating for lower frequencies such as 50Hz and you're multiplying by 0.1. I have those on my pre-amp section sat next to me.. however I know that a better modern power supply for the pre would clear up more noise for the opamps.
Did you have any specific frequency in mind (most regulators such as LDOs drop off over 1MHz)?
As said (and I forgot) - adding additional capacitors in parallel complicates things a little, you end up with multiple poles. I'm not an expert but for the most part - decoupling is better done as close to the device creating the power noise.
If you know the ESR specs for the regulator and can find a parametric search option for ESR from one of the component supplies you can filter for the relevant ones.
Low ESR caps are required for switcher power supplies. The distributor selector tables can search for them.
I've replaced about 700 e-caps since I quit work; only a few were low ESR since I've only fixed about 6 switcher supplies. I buy long life (>3000 hours service life) e-caps from Panasonic, Rubicon, Nichicon, Vishay, Kemet, whatever is in stock at newark(farnell), digikey, mouser. These are premium enough to work every place I have put them, have never need replacing, and aren't low ESR. They weren't described as "audio" caps. By contrast the TV parts store shelf caps like CDE, atomlytic, blue beaver, aerovox (electrolytic) I bought in the 70's were ****, needed replacing every 6000 hours or less. CDE these days has a less stringent end of life spec than the others (read the datasheet), and sources from a country known for lies on the QA paperwork.
I've replaced about 700 e-caps since I quit work; only a few were low ESR since I've only fixed about 6 switcher supplies. I buy long life (>3000 hours service life) e-caps from Panasonic, Rubicon, Nichicon, Vishay, Kemet, whatever is in stock at newark(farnell), digikey, mouser. These are premium enough to work every place I have put them, have never need replacing, and aren't low ESR. They weren't described as "audio" caps. By contrast the TV parts store shelf caps like CDE, atomlytic, blue beaver, aerovox (electrolytic) I bought in the 70's were ****, needed replacing every 6000 hours or less. CDE these days has a less stringent end of life spec than the others (read the datasheet), and sources from a country known for lies on the QA paperwork.
Their type is 'General use' 85/105 C. All Japanese manufacturers are good (actually the best).