Analog ESR/Z meter- finished - Page 1
Forum section: electronics / projects

author: RiverTown
author_rank: Regular Contributor
timestamp: March 07, 2016, 09:53:01 pm
content: Project was finished long ago, but I was quite busy with college. This semester is lot easier so I will present project now.Additional informations about project can be found here:https://www.eevblog.com/forum/beginners/yet-another-esr-meter-project/msg468077/#msg468077https://www.eevblog.com/forum/eda/pcb-layout-comments-and-suggestions/msg502195/#msg502195Most of informations can be found in linked topics so I will try to be short.Schematic:VPCC resistors are calculated for 5V threshold, because my power adapter can maintain 5V at full load. Some adjustments may be necessary depending of external power source.Charge current: 1ACharge termination current around 13mASome of used components:BATT:http://www.ebay.com/itm/2200mAh-NTA2335-Battery-for-Logitech-mm50-Portable-Speaker-System-for-iPod-/251170359973?hash=item3a7aeb8aa5(different connector is used in final design)MCP73871:http://export.farnell.com/microchip/mcp73871-2cci-ml/ic-battery-management-cont-qfn20/dp/1642489TPS79325:http://export.farnell.com/texas-instruments/tps79325dbvr/ic-v-reg-ldo-2-5v-smd-sot-23-5/dp/1460963TPS60403:http://export.farnell.com/texas-instruments/tps60403dbvt/charge-pump-inverter-smd-60403/dp/8457786TPS72325:http://export.farnell.com/texas-instruments/tps72325dbvt/regulator-ldo-fixed-2-5v-sot-23/dp/2323571LTC6244:http://export.farnell.com/linear-technology/ltc6244hms8-pbf/cmos-op-amp-dual-50mhz-ln-8msop/dp/1715052BAT54S:http://export.farnell.com/fairchild-semiconductor/bat54s/diode-schottky-0-2a-30v-sot-23/dp/1467519R18 (TRIM):http://export.farnell.com/alps/rk09k1130c79/potentiometer-10kb/dp/1191741R13 (0,5W, HV):http://export.farnell.com/welwyn/mh37-1mji/resistor-h-v-0-5w-1m/dp/1100301C15 (X2):http://export.farnell.com/vishay/f1778447m3ict0/cap-film-pp-470nf-800v-rad/dp/1413848C1- 3, C12 (1206, 10uF/16V):http://export.farnell.com/multicomp/mc1206f106z160ct/cap-mlcc5v-10uf-1206/dp/1759445RLC6, C11, C13 (1206, 2uF2/16V):http://export.farnell.com/multicomp/mc1206f225z250ct/cap-mlcc-y5v-2-2uf-25v-1206/dp/1759451?selectedCategoryId=&exaMfpn=true&categoryId=&searchRef=SearchLookAheadC7, C8 (0805, 1uF/16V):http://export.farnell.com/multicomp/mc0805b105k160ct/cap-mlcc-x7r-1uf-16v-0805/dp/2320853Other components:Capacitors: 0805, 50VResistors 0805, 1% (except R1- R7 they are 0603 1%)Measurements:Supply ripple 5mV/DIV, 5us/DIVPositiveNegativeOscillator output 1V/DIV, 5us/DIVDivider output and buffer output (20mV/DIV, 5us/DIV)Shunt voltage 50mV/DIV, 5us/DIVAmplifier output 1V/DIV, 5us/DIVSome random pictures:http://www.mediafire.com/view/df080hxn0rqtt4w/PlanOn.pnghttp://www.mediafire.com/view/nbepe6ahe35yaaf/Top.pnghttp://www.mediafire.com/view/cgbw3oqul7tanx3/Bott.pnghttp://www.mediafire.com/view/o3vntqm3d6txm22/IMG_1259.JPGhttp://www.mediafire.com/view/6u2xbb69b3letrt/IMG_1261.JPGhttp://www.mediafire.com/view/0ztrjt47gck9iva/ESR1.JPGhttp://www.mediafire.com/view/wddk01lge0mabi4/ESR2.JPGhttp://www.mediafire.com/view/dmt74mtwtaatmwb/ESR3.JPGhttp://www.mediafire.com/view/oh1ewrj0tpirz39/ESR4.JPGhttp://www.mediafire.com/view/qteqnf6bnr7ittz/ESR5.JPGhttp://www.mediafire.com/view/qpaevlba60yivbi/IMG_1304.JPGFront panel is done in CorelDraw and laser engraved (wasn't cheap), scale is combination od AutoCAD and CorelDraw..Gerber files:http://www.mediafire.com/download/z11xj4ajwmx165e/REV1Gerber.zipEagle files are available via PM...

author: dannyf
author_rank: Super Contributor
timestamp: March 07, 2016, 11:23:09 pm
content: Some quick suggestions, based on a project I did that looks quite similar to yours but worked quite differently.Your output is subject to the diodes non linearity, which can be an issue when high ear shows up. You can solve that but putting the diodes in the feedback loop.The whole design can be made single rail, siify the design.You may pick an ohm meter with the right center resistance marking - your meter has reciprocal reading, like most ohm meters.The oscillator can be made to much like a sin oscillator by adding a capacitor.For insensitive meters ( over 1ma full scale), a buffer, like emitter follower can be used.Like yous, my meter is also designed around a dual opamp: one opamp functions like an oscillator, almost identical to yours.My second stage is a non-inverting amp, with the dut from the inverting end to ground, and the diodes plus the meter in the feedback loop.It has excellent range and calibrates very nicely to theoretical levels, as any non linearity is handled by the opamp.Very compact. As a matter of fact, I build one for a friend Manhattan style on a ne5532.

author: dannyf
author_rank: Super Contributor
timestamp: March 07, 2016, 11:50:41 pm
content: I went back to your old thread and read about your initial approach with a transformer.A good source for HF transformer is CFL light bulbs. All you need is a 10 or 20 to 1 turn ratio. Compact and easy to diy.But I generally agree that the use of transformers as an impedance converter is a flawed approach. In my set up, with the dut not on the signal path, the opamp essentially plays as an impedance converter.

author: RiverTown
author_rank: Regular Contributor
timestamp: March 08, 2016, 10:55:19 am
content: Quote from: dannyf on March 07, 2016, 11:23:09 pmYes, I'm aware that diode nonlinearity has negative influence on measuring high esr. But it helps with measuring low esr values, as is seen from LTspice plot in other topic, and that is more important for me.Battery voltage was too low for the circuit so I had a choice to use single supply rail and boost converter + one regulator, of voltage inverter and two regulators. At the end I decided to go with option no.2.Thanks for the tip about adding capacitor to get sine alike signal, that is good advice.Yes, dropping transformer approach idea was good thing. But thanks for the tips regarding supply of switching transformers, and windings. This can be helpful on some other project.

author: dannyf
author_rank: Super Contributor
timestamp: March 08, 2016, 12:12:55 pm
content: "But it helps with measuring low esr values, as is seen from LTspice plot in other topic, and that is more important for me."I will take a look at that thread but it seems counter intuitive in that a precision rectifier provides the same performance in low ESR cases and better performance at high ESR.Also, if you want to focus on low res, use a lower value resistor in serial with the dut (10ohm now) - that resistor dictates the center value of your ESR reading. Or you have to recalibrate the meter.

author: RiverTown
author_rank: Regular Contributor
timestamp: March 09, 2016, 05:54:48 pm
content: I meant to say that nonlinearity of diodes changes scale deflection vs esr from linear to exponential, which in this case increases resolution on smaller esr values.Meter is manually calibrated with bunch of 1 ohm 1% resistors. Two of them in parallel to form 0.5 ohm resistor, and then every other in series. That allowed me to draw a scale with 0.5ohm resolution. Not ideal but works for me.