Timeline for What is the correct schematic symbol to use for virtual ground?
Current License: CC BY-SA 4.0
16 events
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| Apr 16, 2019 at 20:31 | history | edited | not2qubit | CC BY-SA 4.0 |
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| Apr 16, 2019 at 20:21 | history | edited | not2qubit | CC BY-SA 4.0 |
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| Apr 16, 2019 at 7:56 | comment | added | Transistor | @not2: In the filters you mention the capacitors are always part of an RC network and so never "short" the output of the op-amp. In your first circuit any noise on the supply is yanking the op-amps output up and down as the output is directly coupled to the supply rails. That's not good. Instead, decouple the supply rails by placing a capacitor between V+ and GND as close as possible to the chip and then trust the op-amp to work normally using C1 in my Figure 1 to provide stability. | |
| Apr 16, 2019 at 6:48 | vote | accept | not2qubit | ||
| Apr 16, 2019 at 6:48 | answer | added | not2qubit | timeline score: 0 | |
| Apr 15, 2019 at 20:23 | history | edited | not2qubit | CC BY-SA 4.0 |
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| Apr 15, 2019 at 20:02 | comment | added | not2qubit | @Huisman Yeah I know about the pin numbers being completely off, but I forgot to mention it in OP. Spehro & Justme: I don't understand what is the problem with using caps on the output of an opamp,because I see this all the time in both active and passive Low Pass Filters. In fact the driver above is part of a greater circuit with using such filters. | |
| Apr 15, 2019 at 19:16 | comment | added | Huisman | Did you notice the numbers around U1 don't match with the pin numbers of a AD8607. | |
| Apr 15, 2019 at 17:49 | answer | added | Transistor | timeline score: 6 | |
| Apr 15, 2019 at 17:34 | comment | added | Spehro 'speff' Pefhany | Check out the datasheet. This op-amp is capable of 2nF loading without oscillation, which is actually unusually good (especially for a low-power op-amp), and they promote it as a feature. So if C2/C102 were reduced to 1nF it might be okay. There are dedicated rail splitter chips that replace that whole mess. Eg. TLE2426 or you can add compensation if you really want to use an op-amp. | |
| Apr 15, 2019 at 16:41 | comment | added | Justme | Usually, capacitors are not connected directly to op-amp output. They don't like it. The circuit looks like it's made by a beginner, or for beginners, to have something to work on a concept called virtual ground. In this case, virtual ground is just VDD/2, half of the supply voltage, buffered by an op-amp. | |
| Apr 15, 2019 at 16:36 | comment | added | not2qubit | @SpehroPefhany Oh!? Thanks for that pointer. Clearly I need to find another way to provide whatever that voltage is. Any possibility you could clarify or link me to how to better understand the problem you mentioned? | |
| Apr 15, 2019 at 16:33 | comment | added | Chu | You don't really 'provide' a virtual ground - it just happens as a consequence of the configuration. | |
| Apr 15, 2019 at 16:32 | history | edited | not2qubit | CC BY-SA 4.0 |
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| Apr 15, 2019 at 16:30 | comment | added | Spehro 'speff' Pefhany | The naming of the net is not the most serious problem with that circuit. It's way over the 2nF recommended capacitive loading and will likely oscillate and get hot. | |
| Apr 15, 2019 at 16:24 | history | asked | not2qubit | CC BY-SA 4.0 |