Any IC for measuring RMS voltage? - Page 1
Forum section: electronics / projects

author: Manx
author_rank: Contributor
timestamp: June 10, 2020, 10:24:58 am
content: I need to measure RMS voltage of pulsed DC, in the range up to ~100 mV, with at least 16 bit resolution, from two channels, and output it via I2C (preferably) or SPI. Supply is 3.3 V. I don't want to calculate the RMS voltage myself and I'd like to use some ready-made integrated solution.Unfortunately, I cannot find any IC that could do this. I only found some RMS-to-DC converters, that I could put before the existing slow ADC interfacing with slow and small microcontroller. These converters are however very expensive compared to the cost of other components (and I'd need two of them). Also, at least the ones I found, need dual supply.Do you know of any IC that may be of use to me?

author: dzseki
author_rank: Frequent Contributor
timestamp: June 10, 2020, 10:47:16 am
content: For a pulsed DC signal (that is a square wave in nature) the RMS is the same as the average, and you can obtain the average by a simple low pass filtering, no?

author: coromonadalix
author_rank: Super Contributor
timestamp: June 10, 2020, 11:26:57 am
content: You have the famous ad636 or ad637 used in multimeters ?

author: Manx
author_rank: Contributor
timestamp: June 10, 2020, 01:54:40 pm
content: By "pulsed" I mean rectified AC. Or worse.@coromonadalix , AD636 was what I had in mind when I was thinking about RMS-to-DC converters. The problem is, when used with a single supply, it requires 5 V. I have only 3.3 V.BTW, are they really famous and used in multimeters? Like, are they THE chips for the job?

author: Wytnucls
author_rank: Super Contributor
timestamp: June 10, 2020, 02:19:42 pm
content: AD 736/737Wide power supply range: ±2.5 V to ±16.5 V

author: coromonadalix
author_rank: Super Contributor
timestamp: June 10, 2020, 02:31:59 pm
content: You can use icl 7660 to do some voltages conversions, like creating negatives voltages ...For the rms converters chips, Maxim as a few, Intersil too, but in the end they do the same jobs, unless you have very specific needs / use ?

author: Kleinstein
author_rank: Super Contributor
timestamp: June 10, 2020, 03:56:08 pm
content: There are also chips made for power meters. These usually have some 2 ADCs and some DSP function to calculate the true power. An example would be the ADE7753, but there are others too.Many of them also offer direct RMS and similar readings. These chips are quite powerful and due to the large numbers they are used in metering they are surprisingly cheap.

author: Benta
author_rank: Super Contributor
timestamp: June 10, 2020, 04:20:19 pm
content: Quote from: dzseki on June 10, 2020, 10:47:16 amUmm, no.

author: Manx
author_rank: Contributor
timestamp: June 10, 2020, 09:14:49 pm
content: Thank you very much for your help.Thanks for pointing me towards ICL7660. I think for now I will use it with AD736 to make the current prototype work with pulsed DC.Thanks for pointing me towards power meters. I found MCP39F521 and it looks nice at the first glance. I'll probably use it (or something like it) in the future as they are very cheap and seem to do what I want.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 10, 2020, 09:21:08 pm
content: The LTC1966 is rated for a supply voltage of 2.7 to 12 volt.

author: Manx
author_rank: Contributor
timestamp: June 10, 2020, 11:10:09 pm
content: Thanks VERY much! LTC1966 seems like the way to go.