Op amp substitution - Page 1
Forum section: electronics / beginners

author: Raj
author_rank: Frequent Contributor
timestamp: October 12, 2021, 05:05:56 am
content: I was gonna make a project from the magazine Elektor. Only problem is, I can't get the op amp that was needed for it. The op amp is TS924INAttached: OP amp description.Is any Quad channel pin compatible Rail-to-Rail Low-Noise Op Amp with output current of >20mA or 80mA gonna suffice? Or is there more to Op amps?I was thinking of getting TL974 or TLC085CN unless I can't buy them either (getting stuff from mouser is hard for Indian hobbyists since you need government import license) (Even getting a Chinese fake/recycled is tough, not saying all IC from china are fake but...since Aliexpress throws a warning when you checkout with Indian address)

author: ledtester
author_rank: Super Contributor
timestamp: October 12, 2021, 03:40:24 pm
content: Can you provide a link to the project article or the issue (month/year) it appeared in?Looks like some sort of LC-tank oscillator. I would probably just try it with the op-amps you have on hand and see how much current you can get out of it.

author: Raj
author_rank: Frequent Contributor
timestamp: October 12, 2021, 04:40:37 pm
content: yup. It's the 6th edition of 2006. I too think, high amperage only matters for the injector...maybe one can make a separate injector circuit using single channel opamp if suitable match is unavailable, I couldn't get the 74hc4040 either but maybe I can replace that with a microcontroller or 74hc4024 or 4040but damn, aren't components getting hard to get.

author: eblc1388
author_rank: Frequent Contributor
timestamp: October 14, 2021, 09:08:58 am
content: Quote from: Raj on October 12, 2021, 05:05:56 amThe original designer has opted for a very special Quad Op amp. It must be working with rail-to-rail output, at a total supply voltage of 3V and capable of providing 80mA output current. You will be struggling to find a common replacement opamp. The TL974 will be good for 3/4 of your circuit requirement but it has a very low output current. Possibly you can add an output current amplifying stage for the part which deal with the generation of the injection current.

author: tooki
author_rank: Super Contributor
timestamp: October 14, 2021, 11:45:01 am
content: Quote from: Raj on October 12, 2021, 05:05:56 amThe bigger problem is that the TS924IN (the DIP package) is obsolete. That might also explain the difficulty in finding it. You’ll need to either redesign the PCB to use one of the SMD versions, or use a breakout board to turn an SMD version into a DIP.Surely there must be a legitimate ST distributor within India that you can order from?Also, read the datasheet carefully. It describes the single and dual, and “smaller package” versions of the chip. So if, for example, you can’t get the quad version, but can get the dual, you could make a breakout board that holds two of the duals.

author: Raj
author_rank: Frequent Contributor
timestamp: October 14, 2021, 12:55:40 pm
content: Quote from: tooki on October 14, 2021, 11:45:01 amSure. TS924IDT looks like a valid replacement to me. Only problem, finding a distributor. It looks like Arrow.com might sell it but I feel uncomfortable buying a single part from them cause last time I bought a power supply, the guys in the middle (like shipping department, excise and duty officers etc etc) kept asking me questions about why I needed it, as if hobby use was totally inconceivable.(despite the fact that I filled it all out, clearly, in the order forum itself.) The tax and shipping was also probably more than the item itself. Maybe when I have a bigger list of stuff, I'll place an order.Quote from: eblc1388 on October 14, 2021, 09:08:58 amIndeed. Good thing I haven't ordered the circuit yet. But still, I'll need a simple quad channel (one channel disabled) rail to rail op amp and a single channel high current rail to rail opamp. No idea on how to select one.I wish I knew if TL974 or TLC085CN or TS924IDT could do the job.

author: tooki
author_rank: Super Contributor
timestamp: October 14, 2021, 01:50:14 pm
content: Quote from: Raj on October 14, 2021, 12:55:40 pmThe TS924IDT is thesame part, just in a different chip package. A simple SMD to DIP breakout board would suffice. This is, by far, the least risky option.The TLC085CN won’t operate at the supply voltage in use, so it’s definitely out.The TL974… maybe? It’s got very asymmetrical output source and sink current capabilities, and I’m not sure what this circuit needs.

author: Raj
author_rank: Frequent Contributor
timestamp: October 14, 2021, 07:10:00 pm
content: Quote from: tooki on October 14, 2021, 01:50:14 pmTS924IDT i'll try to get my hands on then.