Current sensor for low currents - Page 1
Forum section: electronics / projects

author: delicado
author_rank: Contributor
timestamp: June 20, 2017, 04:24:19 am
content: HiI'm trying to measure low DC currents around 0.1A to 1A at 5V. I've heard about the ACS712, but my current never goes above 1A and its resolution is relatively low (around 20mA if my math is correct).What are some (low cost) chips that can measure low values of current at a higher resolution (<2 mA)?Any thought appreciated.

author: BravoV
author_rank: Super Contributor
timestamp: June 20, 2017, 04:27:31 am
content: INA226 ?

author: delicado
author_rank: Contributor
timestamp: June 20, 2017, 04:31:25 am
content: Quote from: BravoV on June 20, 2017, 04:27:31 amI've had a look at INA226 too, but isn't the resolution roughly in the same range?

author: rx8pilot
author_rank: Super Contributor
timestamp: June 20, 2017, 04:32:48 am
content: INA226 is workable. It also has averaging and some other controls which is helpful.It only works with i2c so you get data points. If you need an analog output, it is not the choice.Sent from my horrible mobile....

author: DBecker
author_rank: Frequent Contributor
timestamp: June 20, 2017, 05:08:00 am
content: Do you need isolation?What bandwidth?Do you need precision, accuracy or both? What temperature stability?I've used the ACS712 for safety isolation. It's excellent for that purpose. Generally the measurement challenges are bandwidth and noise, but it can also be influenced by movement and strong nearby fields.I've mostly seen the '226 used for power usage monitoring in the same voltage domain. It's the go-to part when you are willing to build a special development board to track power management, with one monitoring each branch of the supply. Putting a hundred on a board only requires I2C expanders, with far fewer hardware design challenges than any other approach.

author: DaJMasta
author_rank: Super Contributor
timestamp: June 20, 2017, 05:41:23 am
content: Dunno if there's something in your design that prevents it, but especially if you have a free ADC channel, you could just build one up from a handful of parts.For a high side current amp, you just need a shunt, an opamp or two, and some resistors. You can scale the gain of the amplifiers to your expected sensing range (if your max is 1A and your shunt is 100mOhm, then a gain of 50 in the amplifiers would get that to 0-5V), and then you can make maximum use of your ADC's resolution, this would give you 1024 divisions of 1A with a basic 10 bit ADC.Now that option won't be as well characterized as an integrated solution, and unless you're willing to do the testing and compensation yourself, it will be more susceptible to errors from temperature, ADC reference fluctuation, etc. than a single chip... but you can get basically any range you want (within reason and without a need for isolation) with less than 50 cents of parts in one off quantities if you've got an ADC channel open.

author: Fungus
author_rank: Super Contributor
timestamp: June 20, 2017, 11:51:08 am
content: Quote from: delicado on June 20, 2017, 04:24:19 amGet a 0.1 Ohm precision resistor and an op-amp. Put it series, amplify the voltage drop across it, measure it.

author: fcb
author_rank: Super Contributor
timestamp: June 20, 2017, 12:09:58 pm
content: ZXCT1009 is quite neat part.https://www.diodes.com/assets/Datasheets/ZXCT1009.pdf

author: ahbushnell
author_rank: Frequent Contributor
timestamp: June 20, 2017, 01:07:53 pm
content: Quote from: fcb on June 20, 2017, 12:09:58 pmI like that.

author: LukeW
author_rank: Frequent Contributor
timestamp: June 24, 2017, 07:31:59 am
content: Quote from: fcb on June 20, 2017, 12:09:58 pmJust wondering if anybody has a quick answer without looking up the datasheet... what's the difference between ZXCT1009 and ZXCT1109?

author: fcb
author_rank: Super Contributor
timestamp: June 24, 2017, 09:07:40 am
content: Different maximum differential voltages: 20v for the 1009 and 40v for the 1109.