opamps in parallel?  - Page 1
Forum section: electronics / projects

author: BiOzZ
author_rank: Regular Contributor
timestamp: July 25, 2013, 06:37:56 pm
content: im using a THS3001 420mhz opamp for a personal project but i would only feel safe yanking 100ma out of them and i would love them to work to 400ma .. is there any problems in sticking 4 high speed opamps in parallel? there going to have an adjustable gain around 1-10... or should i use one for amplification and 4 in parallel for a voltage follower? or just live with the fact that i only can use one?im not a highspeed electronics guy i dont want to create a separate high speed current amp ...OH im only using this to 40mhz sinewave and this is a personal project ... i simply have 10 of these things around that i refuse to stick on to a spool so if there is a loss in bandwidth im fine to up and about 10ns but can go really to 25 or soer down to? ... not importantthanks!

author: fcb
author_rank: Super Contributor
timestamp: July 25, 2013, 06:46:17 pm
content: There was an interesting bit in this weeks teardown of the Siglent generator that might be relevant (the bit covering the output buffer) - Dave showed a snapshot off an app note that showed 4 opamps in parallel.

author: free_electron
author_rank: Super Contributor
timestamp: July 25, 2013, 06:53:57 pm
content: agilent does that in ther 33250 generators as well. some opamps are designed for that.

author: jmole
author_rank: Regular Contributor
timestamp: July 25, 2013, 07:33:46 pm
content: Most opamps will have a positive tempco with respect to output drive, so you ought to be okay doing this. Big worry is offset voltage, but the PTC effect can fix this to some extent.Adding a resistor to the feedback path (instead of a direct connection) will decrease your bandwidth to some extent and may reduce ringing at a gain of 1, but the most common solution is to add a low-value resistor to the output of each amp and connect the other end to a common output node.High-speed stuff is tricky, so good luck!

author: Marco
author_rank: Super Contributor
timestamp: July 26, 2013, 02:28:54 pm
content: Can't you just use a transistor to boost the current?

author: uoficowboy
author_rank: Regular Contributor
timestamp: July 26, 2013, 02:55:42 pm
content: I would think that, unless they're nicely matched, they would end up fighting each other a lot.Then again, I know I've seen DIY audio guys doing this so I may be missing something.

author: fcb
author_rank: Super Contributor
timestamp: July 27, 2013, 11:01:52 am
content: You could *theoretically* just add a transistor on the output, but in practice it won't work with out alot of experimentation. You are also going quite fast (40MHz)so including it in the feedback loop is non-trivial.If you've got lots of these THS3001, then I would try paralleling them (with output resistors as per other postings). Just try it, there is far too much talk and simulation these days.

author: EEVblog
author_rank: Unknown
timestamp: July 27, 2013, 01:42:21 pm
content: A possible side benefit of paralleling opamps is also lowering the noise. Although you have to use ballast resistors on the output to isolate them.

author: SArepairman
author_rank: Frequent Contributor
timestamp: July 28, 2013, 07:29:14 am
content: parallel instrumentation amplifiers?I kinda wanna try this just to see what happens