| Electronics > Projects, Designs, and Technical Stuff |
| Any reason I shouldn't use a TL431 as a virtual ground? |
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| Zero999:
--- Quote from: Benta on November 14, 2018, 09:17:53 pm --- --- Quote from: Hero999 on November 14, 2018, 09:05:46 pm --- --- Quote from: imo on November 14, 2018, 02:06:56 pm ---If enough headroom you may try with 78L05. Not centered, but it works. --- End quote --- The only potential problem with the LM78L05 is it can only source current, A virtual ground typically needs to both source and sink current. A resistor and capacitor connected to the output, will enable it to sink some current, as the cost of extra current drain. --- End quote --- OP is buffering the output with an LM358. But I like the TL431 better. --- End quote --- In that case, I think a good old potential divider, with a bypass capacitor on one of the resistors would be a better bet. The output voltage dropping as the power supply voltage will be an advantage, because it will remain biased closer to the optimum operating point, as the battery discharges. The nonsymmetrical output swing of the LM358 can be taken into account when selecting resistor values for the potential divider. |
| Benta:
Problem with the voltage divider is that the PSRR is low, even with decoupling. The TL431 solves that issue. |
| bd139:
That’s exactly the point. |
| Zero999:
--- Quote from: Benta on November 15, 2018, 01:47:11 pm ---Problem with the voltage divider is that the PSRR is low, even with decoupling. The TL431 solves that issue. --- End quote --- --- Quote from: bd139 on November 15, 2018, 01:52:36 pm ---That’s exactly the point. --- End quote --- What do you mean? With appropriate filtering, a voltage divider can have as gooder PSRR, if not better than the TL431, especially at high frequencies. It's a moot point anyway. PSRR is no issue as it's powered from battery which will have no ripple and even if it was powered from a noisy power supply, a single TL431 only will remove the noise from one rail only. Two are needed to get a good PSRR on both rails. |
| bd139:
This is going to have a DC socket on it. It needs to be able to run off battery or 12V DC. If I set the rail at 2.5v approx with a TL431/whatever, the supply voltage change will be in the order of 50nV. If I bias it with a voltage divider I need to accept at that time an instant change of virtual ground from 4.5V to 6V. There are two integrators this isn't going to make very happy. |
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