| Electronics > Projects, Designs, and Technical Stuff |
| Simple Error Amplifier |
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| eujean:
--- Quote from: Benta on March 25, 2017, 03:35:36 pm ---your regulator is open loop. --- End quote --- Not sure I understand, since the final output is fed to the op-amp through the 20k/2k combination? --- Quote ---I see a 100/900 kohm combination at the output. Shouldn't that go to the opamp? --- End quote --- This was only intended to be used for later measurement, i.e. something that can be sent to an ADC or something. |
| Benta:
Vset seems to be a voltage reference with no relation to the output. |
| BravoV:
You're feeding the non-inverting input with a "FIXED" voltage. |
| Kleinstein:
There is feedback through R4 and R5. V_set is relative to the output. The circuit with GND at the positive output can be a little confusing. Still the error amplifier works in linear mode so usually with something like 1 V at the output. So it absolutely makes sense to use an OP and not a comparator. For a comparator linear operation might work in some cases, but is usually not guarantied. Also the LT1037 might be a problem, as this OP is not unity gain stable - this can be a problem in some cases. With the compensation circuit as shown, the choice of OP could be important as the GBW of the OP might set the loop speed in the critical frequency range. So a faster or not unity gain stable OP might need a modified compensation. For stability of the loop also parasitic properties like the ESR of C2 and inductance of the 0.1 Ohms resistor can play a role. Usually it is a good idea to have a combination of low ESR and high ESR capacitance for C2. |
| eujean:
--- Quote from: Kleinstein on March 25, 2017, 05:03:18 pm ---The circuit with GND at the positive output can be a little confusing. --- End quote --- Yes I must apologize for this. I did it this way to relate to the original e3610 schematic. --- Quote ---Still the error amplifier works in linear mode so usually with something like 1 V at the output. So it absolutely makes sense to use an OP and not a comparator. For a comparator linear operation might work in some cases, but is usually not guarantied. Also the LT1037 might be a problem, as this OP is not unity gain stable - this can be a problem in some cases. With the compensation circuit as shown, the choice of OP could be important as the GBW of the OP might set the loop speed in the critical frequency range. So a faster or not unity gain stable OP might need a modified compensation. --- End quote --- This makes sense as Benta mentioned as well that the amplifier is operating in linear mode. With some more simulation, the comparator seemed to oscillate even though it did seem to make the loop a bit faster prior to oscillation. Does this mean that the compensation circuit is of much more importance than the OP? How would one go about deciding what to trade off? |
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