ESR Values for Electrolytic Caps

[smile]

On one PSU the PWM circuit had 50V 0.22caps, that had 10Ohm ESR, the circuit did not work. I replaced the caps with salvaged caps that had ESR of 2Ohms. The circuit (+5VSB) began working.

You seem to be too optimistic quoting 10Ohms.

[wraper]

On one PSU the PWM circuit had 50V 0.22caps, that had 10Ohm ESR, the circuit did not work. I replaced the caps with salvaged caps that had ESR of 2Ohms. The circuit (+5VSB) began working.

You seem to be too optimistic quoting 10Ohms.

2Ohm ESR for 0.22uF cap is very low, most of LOW ESR caps won't have it this low. Even 10 ohm is quite low, certainly not on a high side.

[David Hess]

Those are most likely not in high frequency paths, where you need low esr, so it doesn't really matter.  But I'd expect 4-10 ohm for such capacitors.

For example, you may see such small capacitor on the input of a controller chip, to smooth out the input voltage before the chip gets its power from an auxiliary winding on the transformer. don't need low esr for that.
Could be used in a comparator or opamp for protections, basic simple things that don't need low esr.

They may still need low ESR to suppress ripple from high frequency load current variation.  I call these "bulk decoupling capacitors".  I have seen some power supplies that decoupled the small bulk decoupling capacitor from the load using an inductor and ceramic or film capacitor.

Because of their small volume for electrolyte for a given perimeter of rubber seal at the lead end, their operating life can be limited even in low ripple current applications.  When I change the big output capacitors in a switching power supply, I try to find these and change them also.  These were the first parts to fail in my Craftsman power tool chargers and my Maha MH-C9000 charger.  I have seen a few Tektronix power supplies that only required replacement of the bootstrap capacitor.

[floobydust]

Those are most likely not in high frequency paths, where you need low esr, so it doesn't really matter.  But I'd expect 4-10 ohm for such capacitors.

For example, you may see such small capacitor on the input of a controller chip, to smooth out the input voltage before the chip gets its power from an auxiliary winding on the transformer. don't need low esr for that. [...]

I find the SMPS aux cap must be low ESR. They are typically 10-47uF and commonly fail, I think because the parts see high ripple current spikes with the drive switching on the mosfet. I'm not sure, they simply fail a lot. Some SMPS add a small series resistor like 10Ω feed in series with the cap after the rectifier diode.
47uF 50V ripple current spec. 100kHz varies from is 90-400mA, depending on the part. For the better parts:
Nichicon UPW 300mA at 100kHz, ESR 0.43Ω
Panasonic FR 405mA at 100kHz, ESR 0.14Ω

[The Electrician]

What about ESR for low value caps like, typical used in ATX PSU?

50V 0.33uf; 50V 0.22uf; 50V 0.1uf; 50V 1uf

Why does anybody ever use electrolytic caps in such low capacitance rather than film caps?

[David Hess]

What about ESR for low value caps like, typical used in ATX PSU?

50V 0.33uf; 50V 0.22uf; 50V 0.1uf; 50V 1uf

Why does anybody ever use electrolytic caps in such low capacitance rather than film caps?

They are less expensive, and often their higher ESR is a virtue in bulk decoupling applications.

[The Electrician]

What about ESR for low value caps like, typical used in ATX PSU?

50V 0.33uf; 50V 0.22uf; 50V 0.1uf; 50V 1uf

Why does anybody ever use electrolytic caps in such low capacitance rather than film caps?

They are less expensive, and often their higher ESR is a virtue in bulk decoupling applications.

A quick look at Digikey for .22 uF electrolytics nets some parts all designated "not for new designs".  The prices ranged from 13 cents to 43 cents.

A search for .22 uF film netted so many I didn't look through all of them for price, but I saw some for 30 cents.

You said about the electrolytic ones: "Because of their small volume for electrolyte for a given perimeter of rubber seal at the lead end, their operating life can be limited even in low ripple current applications."

For me, the rather small price difference plus the substantially lower life span would rule out electrolytics.

[wraper]

A quick look at Digikey for .22 uF electrolytics nets some parts all designated "not for new designs".  The prices ranged from 13 cents to 43 cents.

A search for .22 uF film netted so many I didn't look through all of them for price, but I saw some for 30 cents.

Those prices are more than an order of magnitude higher than what manufacturer would pay for volume production. The price difference may not look that important for you but its a huge deal for mass production of inexpensive consumer devices.

[madires]

A quick look at Digikey for .22 uF electrolytics nets some parts all designated "not for new designs".  The prices ranged from 13 cents to 43 cents.

A search for .22 uF film netted so many I didn't look through all of them for price, but I saw some for 30 cents.

A local online shop sells a single MLCC (0805, X7R, 220nF, 50V, 125°C, Kemet) for 3 euro cents.

[Jeff eelcr]

My answer is 12 and you put the decimal point where ever it fits as in
.012, .12, 1.2, 12.0, 120.0 fits most applications, note numbers may
vary also.
Jeff