Where are all the ESR meters?

..by at least a few orders of magnitude!

by doing this:

Ckt ---------+ o | o

Maybe a power resistor in there so it doesn't go bang when you short out that 400V electrolytic.

--

John Devereux

Why would you expect the ESR to change in those type of capacitors? Any defect in the inner connections would be obvious, because the cap would disintegrate.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

So, you want to flash the silver off the contacts to metalize the insides of the switch's body, or even weld them together?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I know where you're coming from with that statement and it is not true. I am far enough along to know for sure whether something will work or not. All you have thought of so far is measuring the in-phase component of voltage developed by a current pulse. And your typical white board brainstorming is largely used for the how and not the what. The idea within the original Italian hobby circuit was not too bad, the execution was lacking, and the outputs of interest were sort of compressed, but the idea of a bridge driven by a reasonably *low* impedance current source, resulting in short transient recovery from the ESL and limited peak response, is not bad at all.

A better idea, I think, is to use a proper higher-impedance current source, and drive with a 100kHz sine wave, thereby greatly reducing the ESL problem, which can otherwise be a killer for the 1 to 30 milliohm region. Using a sine wave also means the measured ESR can be compared with laboratory meter readings. Otherwise, how would one compare sets of square-wave readings with accurate lab instrument readings?

I'm thinking of using a 2-volt peak sine wave with a 200-ohm resistor (10mA peak test current) delivered from a rail-to- rail opamp with a slew rate exceeding say 2V/us. I'll break the resistor into three parts and add two sets of protection diodes to the rails. The outermost resistor can be a 100-ohm 10-watt high-thermal-mass part to discharge the capacitors.

2-volt P-P is too high to do in-circuit testing in all cases as it could cause Si junctions to conduct. 0.2V or 0.3V would be a lot better.

Some of the designs out there don't bother with discharging the capacitor- they put a low (and stable) -ESR cap of a few uF in series with the DUT. That way you have an upper limit on the energy to be handled (given an upper limit on the voltage of (say) 400VDC or 500VDC to handle off-line filter caps).

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

If the DUT is a large capacitor charged to several hundred volts, that would have to be one heck of a switch.

I think it would be far better to make a current source and voltage preamp that can both withstand several hundred volts.

Neither the current source nor the voltage preamp needs to be super good they just have to not crosstalk. Assuming we have well regulated

+/- 12V supplies, the current source can be just a rail to rail output driving a resistor. For a measurement current of 1mA, a 12K resistor would be required. Assuming we have to withstand 500V, we need a resistor that can take a 21W pulse.

Operating at 1mA results in about a 1uV measurement requirement. This would let us use a resistor on the order of 100K on the input of the preamp without getting swamped with noise.

Do some of you readers have a suggestion for a low- power 5-volt opamp with specs like: 2MHz or higher fT, 2V/us or faster slewing, rail-to-rail output that can deliver 10mA or more while within 500mv of the rail, and of course, low cost? Should be easy to find. :-)

How about a low-power low-cost 5V instrumentation amp?

[snip]

I'm with you on that, even the frequency.

I've been thinking along the lines of an AC _current_source_, and using the cap UT as the filter to keep it queued. Then you get a linear reading of ESR.

But I've been lacking time to put pencil to paper... I'm up to my gills in (paying) projects... and, in my business, one must make money while it's available ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

[snip]

One has to wonder.

I've been thru all kinds of shit tracing my leg pain to crushed disks, only to finally have someone say, "Why don't we take an X-ray of your hip".

Looks like that's the culprit :-(

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

10 mA won't make much voltage across an electrolytic cap!

The other possibility is to just limit the current, not instantly discharge the cap,

John

Synchronous detector?

John

Without pencil to paper, synchronous _may_ allow separation of real and imaginary terms.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

If the drive is a sine wave, ESL peaks go away.

And what is a "*low* impedance current source"?

John

Without pencil to paper, I know it will separate the real and imaginary components enough to improve ESR resolution substantially.

1 uF at 100 KHz has a reactance of 1.6 ohms; you don't need a pencil to figure that out!

John

Go stand in the corner for 15 minutes. You are getting entirely too pisssy. And don't do THAT in the corner.

AD8615?

--

John Devereux