How should I power multiple op-amp in a circuit? - Page 1
Forum section: electronics / beginners

author: vishalkr123
author_rank: Contributor
timestamp: January 11, 2024, 04:49:40 am
content: I was trying to reproduce this very interesting paper (https://doi.org/10.1119/1.3531961) on charge sniffer device. The device shows different colors depending on the charge. This video shows the operation (https://youtu.be/vAQ64Sv4iqY). But I always have confusion regarding powering of op-amps. For example, here two LF411 op-amps are used, but I am not sure how to power them. Should I tie the positive to +9V and the negative to ground. I am trying to build it on a PCB board and does not have a dual rail supply available.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 11, 2024, 05:17:49 am
content: Well, it looks like the circuit is designed to use a dual rail supply.You could use something like the LM7660 to generate a negative rail from the +9V.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 11, 2024, 05:50:21 am
content: According to the original text in the published paper, the dual rail supply appears to come from two 9V batteries, feeding a 6V zener shunt regulator on both rails (see Figure 2).When designing your PCB, you must retain the three separate power rails; positive, negative, and ground. Do NOT connect negative to ground, your circuit will no longer function properly.As suggested, the 7660 is a relatively simple way of generating the negative rail.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 11, 2024, 10:07:29 am
content: The LM3915 should also get away with a lower supply (e.g. +-4 V). So could use a virtual ground and split the 9 V battery voltage to something like a +6 and -3 V. As most of the power would be from the LED driver side this could be a simple zener (or LED) for the ~ 3 V part. It depends on the actual input range if the lowe supply works.The LF411 is not that great for low voltage operation as one looses quite a bit on the negative side. There many more suitable FET based OP amps, e.g. a TLC272 as an older one.

author: vishalkr123
author_rank: Contributor
timestamp: January 11, 2024, 06:51:52 pm
content: Thanks for the suggestions. I have a few more questions:1. Basically, LM7660 gives the negative voltage as output. So, the negative output of the LM7660 along with the positive and ground of the input forms the three inputs for the circuit?2. I don't have LF411 or TLC272 available here. Can I use LF356N instead?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 11, 2024, 07:33:48 pm
content: Yes the ICL7660 (or similar) to gether with capacitors atached produces a negative voltage. I am however not sure the 7660 actually would work with 9 V - this may be too high for the chip.The LF356 could work in principle, but it is a bit power hungry. This could especially be an issue when paired with the 7660 that can only provide a limited current.Another rather close substitute for the old LF411 are the LF351,LF353, TL071 / TL072 / TL082. The circuit contains 2 OPs and could thus well use a dual OP version.A TL061 / TL062 are slower, lower power versions that would also work.There are many other versions that can work. some may need a reduced supply (e.g. +3 and -2 V for the OPs and then +7 and -2 for the LM3915).

author: vishalkr123
author_rank: Contributor
timestamp: January 11, 2024, 08:49:55 pm
content: Thanks. LF351 and LF353 are available.

author: vishalkr123
author_rank: Contributor
timestamp: January 11, 2024, 09:14:00 pm
content: TC7662 seems like a good alternative. It can accept 3V to 18V.

author: Terry Bites
author_rank: Super Contributor
timestamp: January 12, 2024, 03:02:27 pm
content: I made one of these a couple of years back.www.edn.com/detect-charged-bodies-with-electronic-electroscope/It was good enough. I tried it on stripboard and it failed but I got it working on FR4 in Manhattan style.

author: vishalkr123
author_rank: Contributor
timestamp: January 29, 2024, 06:53:40 am
content: Thanks for all the help.Sharing with you all the result of the project that I have been working on at home, on the detection of electrostatic charge. Here is the YouTube link:https://youtu.be/oSSDqfySZ8k.

author: ledtester
author_rank: Super Contributor
timestamp: January 29, 2024, 07:48:31 am
content: Quote from: Terry Bites on January 12, 2024, 03:02:27 pmHere's another "charge wand" used in this Royal Institute demo (starting at 2:30):High-voltage physics - with David Ricketts -- The Royal Institutehttps://www.youtube.com/watch?v=0WWjCICqDK8&t=2m30sand closer view of the wand may be seen at 11:11 (see attached pic).Looks like four resistors, two caps, two solid-state devices, a 9V battery and two wires running up the wand. From the way the presenter uses the device there also appears to be power and reset switches on the bottle cap.

author: MarkT
author_rank: Frequent Contributor
timestamp: January 29, 2024, 03:58:36 pm
content: If you want the top of the range electroscope, there's the ADA4530-1 opamp, its very pricey but guarantees < +/-20 femtoamps bias current upto 85C, typical bias current <1fA, and +/-50µV offset too come to that.... 1fA is about 6000 electrons a second...